Search

Background: Repeat sports-related concussive/subconcussive injury (RC/SCI) is related to memory impairment. Objective & Methods: We sought to determine memory differences between persons with RC/SC...

Introduction We examined the relationship between depression and anxiety, language, and functional outcomes in persons with traumatic brain injury (TBI). Methods The sample consisted of 48 acute TBI (ATBI: 23 Spanish-English Bilinguals; 25 English monolinguals), 30 chronic TBI (CTBI: 17 Spanish English Bilinguals; 12 English monolinguals), and 47 healthy comparison (HC: 29 Spanish-English Bilinguals; 18 English monolinguals) participants. The Hospital Anxiety and Depression Scale was used to measure depression (HADS-D) and anxiety (HADS-A). The Mayo Portland Adaptability Inventory-4 (MPAI-4) was used to measure functional outcomes (ability, adjustment, participation). Results An ANCOVA, controlling for age, revealed the ATBI group reported lower anxiety levels compared to the CTBI group, p = 0.034 np2 = 0.06. HC participants demonstrated significantly higher functional ability compared to both TBI groups, p Conclusion Our results suggest that a relationship between anxiety and depressive symptoms is related more to functional outcomes in monolingual TBI survivors compared to bilingual TBI survivors.

Objective Traumatic brain injury (TBI) survivors exhibit cognitive deficits. Research suggests that multilingualism can influence neurocognitive performance. We examined the effects of TBI and bilingualism/monolingualism on a test of attention and cognitive speed (i.e., Symbol Digit Modalities Test; SDMT). Method The sample consisted of 55 healthy comparison (27 Spanish-English bilinguals; 28 English-monolinguals), 34 acute TBI (14 Spanish-English bilinguals; 23 English-monolinguals), and 27 chronic TBI (13 Spanish-English bilinguals; 12 English-monolinguals) participants. Acute TBI participants were tested 6 months post-injury; chronic TBI participants were tested 12 months or more post-injury. A series of 3X2 ANOVAs were conducted to determine the effect of TBI and language on SDMT written and oral performance. Results ANOVAs revealed the healthy comparison group outperformed both TBI groups on SDMT written, p = 0.000, ηp2 = 0.21. Also, the healthy comparison and chronic TBI groups outperformed the acute TBI group on SDMT oral, p = 0.000, ηp2 = 0.13. Interaction effects emerged between TBI and bilingualism/monolingualism. On SDMT written and oral, acute TBI English-monolinguals outperformed acute TBI Spanish-English bilinguals; meanwhile, chronic TBI Spanish-English bilinguals outperformed chronic TBI English-monolinguals, p Conclusion The acute TBI group performed worse than healthy comparison adults on both SDMT tasks. Furthermore, the chronic TBI group demonstrated better SDMT oral abilities compared to the acute TBI group. Relative to monolinguals with TBI, our findings suggest better cognitive recovery of attention and cognitive speed in bilingual TBI participants. Future studies with larger sample sizes should examine if learning English first or second impacts Spanish-English bilingual TBI survivors’ SDMT performance compared to English-monolingual TBI survivors.

Objective We examined perceived workload as it is related to Brief Visual Memory Test-Revised (BVMT-R) short-delay and long-delay performance in traumatic brain injury (TBI) and healthy comparison (HC) participants. Method The sample consisted of 39 TBI participants and 54 HC participants. Demographically corrected BVMT-R scores were used to evaluate short-delay and long-delay performances. The perceived workload was measured using the NASA-TLX. Results ANOVA revealed that the HC group outperformed the TBI group on the BVMT-R short-delay and long-delay score, p Conclusions Results revealed that TBI participants demonstrated worse BVMT-R performances than HC participants. However, TBI survivors reported higher perceived workload demands compared to the HC group in both short-delay and long-delay of the BVMT-R. Our findings suggest that TBI impacts non-verbal memory performance in both BVMT-R short-delay and long-delay. Also, brain injury may be impacting TBI survivors’ awareness of their non-verbal memory performance. Further work is required to determine what drives the impaired perception of non-verbal memory performance among TBI survivors.

Objective Research shows that traumatic brain injury (TBI) patients perform worse than healthy comparisons (HC) on the Symbol Digit Modalities Test (SDMT). We evaluated cut-off scores for a newly developed recognition trial of the SDMT as a performance validity assessment in monolingual and bilingual TBI survivors and HC adults. Method The sample consisted of 43 acute TBI (ATBI; 24 monolinguals; 19 bilinguals), 32 chronic TBI (CTBI; 13 monolinguals; 19 bilinguals), and 57 HC (24 monolinguals; 33 bilinguals) participants. All participants received standardized administration of the SDMT. None of the participants displayed motivation for feigning cognitive deficits. Results The HC group outperformed both TBI groups on the demographically adjusted SDMT scores, p = 0.000, ηp2 = 0.24. An interaction emerged in SDMT scores where monolingual ATBI outperformed bilingual ATBI and bilingual CTBI outperformed monolingual CTBI, p = 0.017, ηp2 = 0.06. No differences were found in the SDMT recognition trial. Both Bichlmeier and Boone’s suggested cut-off scores had different failure rates in ATBI (Bichlmeier: 77%; Boone: 37%), CTBI (Bichlmeier: 69%; Boone: 19%), and HC (Bichlmeier: 56%; Boone: 26%). For the monolingual group (Bichlmeier: 66%; Boone: 36%) and the bilingual group (Bichlmeier: 66%; Boone: 21%). Finally, chi-squared analysis revealed monolingual TBI had greater failure rates than the bilingual ATBI. Conclusion Bichlmeier’s proposed cut-off score resulted in greater failure rates in TBI survivors compared to Boone’s suggested cut-off score. Furthermore, monolingual ATBI were influenced more by Bichlmeier’s cut-off score than the bilingual ATBI group, although the reason for this finding is unclear and requires additional study with a larger sample size.

Introduction We examined the impact of perceived workload and depressive symptoms on Rey-15 plus recognition (RMT) in ethnic minority participants with traumatic brain injury (TBI). Methods The sample consisted of 63 healthy comparison [HC: 38 with ethnic minority status (EM) & 25 non-ethnic minority Caucasian (NEM)] participants and 40 persons with TBI (18 EM; 22 NEM). The Hospital Anxiety and Depression Scale to measure depressive symptoms (HADS-D) and the NASA-Task Load Index (NASA TLX) to measure perceived workload. Results ANCOVAs revealed that NEM outperformed EM on the RMT, p = 0.000, ηp2 = 0.37. TBI survivors reported higher levels of HADS-D compared to HC participants, p = 0.018, ηp2 = 0.06. Additionally, the EM group reported higher levels of frustration on the RMT compared to NEMs, p = 0.033, ηp2 = 0.05. Interactions emerged for physical demand where NEM participant’s with TBI had higher ratings than EM participants with TBI. For HCs, the EM participants provided higher physical demand ratings than their NEM counterparts, p = 0.029, ηp2 = 0.05. Additionally, a significant relationship between HADS-D and RMT was observed in the healthy NEM participants (r = −0.558, p = 0.004) and NEM participants with TBI (r = −0.288, p = 0.080). Finally, significant relationships between HADS-D and mental demand, physical demand, temporal demand, frustration, and overall subjective workload were observed in healthy EM participants, r = 0.342–0.431, p Conclusion Consistent with previous research, TBI survivors reported higher levels of depressive symptoms, which were associated with RMT performances. Overall, our data suggest the relationship between perceived workload, depression, and performance is complex and that investigators should interpret performance validity scores in person with TBI, depression, and/or EM status with great care.

Objective The Dot Counting Test (DCT) is a performance validity test. McCaul et al. (2018) recently revised the DCT cut-off score from ≥17 to 13.80; we evaluated the new cut-off in non-Latinx Caucasian and Caucasian Latinx traumatic brain injury (TBI) survivors and healthy comparison (HC) participants. Method The sample consisted of 37 acute TBI (ATBI; 11 Caucasian Latinx; 26 non-Latinx Caucasian), 27 chronic TBI (CTBI; 10 Caucasian Latinx; 17 non-Latinx Caucasian), and 55 HC (29 Caucasian Latinx; 26 non-Latinx Caucasian) participants. Results An ANCOVA, controlling for age, revealed no DCT E-scores differences between groups. Both the conventional and the new cut-off scores had different failure rates in ATBI (conventional cut-off: 0%; PNC: 16%), CTBI (conventional cut-off: 7%; PNC: 15%), and HC (conventional cut-off: 10%; PNC: 11%) participants. For the Caucasian Latinx group (conventional cut-off: 6%; PNC: 12%) and the non-Latinx Caucasian group (conventional cut-off: 6%; PNC: 14%), demonstrated different failure rates across cut-off scores. Group differences were found with the McCaul et al. (2018) cut-off and the conventional cut-off. Also, chi-squared analysis revealed non-Latinx Caucasian participants with ATBI had greater failure rates than Caucasian Latinx participants with ATBI. Conclusion The new DCT cut-off score resulted in greater failure rates in TBI survivors. Also, this effect appears to be most pronounced in non-Latinx Caucasian persons with ATBI. Future work should investigate possible reasons for these differences so that more stringent DCT can be utilized in a way that provides less biased results for brain injury survivors across racial and ethnic groups.

The cognitive dynamic system (CDS) is a structured physical model and research tool inspired by certain features of the human brain. One such feature is the predictive adaptation of the organism to the future environment. From an engineering perspective, this property of the brain is of profound practical importance, particularly when the system, in the pursuit of goals or performing tasks, confronts unexpected adverse events or obstacles, which in the aggregate are commonly referred to as risk . To avert risk efficiently, much of the information processed in the past by the CDS is available for processing new information in one of the system’s components termed the perceptor . In the face of uncertainty, the perceptor will provide the processed information to the executive in order for the latter to avoid probable risk. To that effect, the executive will be fitted with Bayesian filtering mechanisms that will guide the CDS to its goal through timely risk-avoiding actions. Those mechanisms not only have unique engineering applications but also potential value for understanding the predictive-adaptation property of the brain, which modern neuroscience attributes to the prefrontal cortex.

Throughout the nervous system, posterior structures are mainly devoted to receptive functions—sensation and perception—while anterior structures are devoted to motor functions. In the cortex, that dichotomy is unclear because perception and action are intertwined in the perception–action cycle, the biocybernetic cycle that adapts the organism to its environment. All neural systems store information (memory), which they enact in behavior and language. There are no “systems of memory” but the memory of systems. The cortex of the frontal lobe is a hierarchical system: motor cortex at the bottom for coordination of simple movements, and prefrontal cortex at the top for complex goal-directed actions. In the coordination of such actions, the frontal hierarchy engages the posterior (perceptual) cortex in the perception–action cycle. Inputs to the cycle come to prefrontal cortex from sensory-evoked perceptual memory and biologic (phyletic) memory. The first comes from neocortex, the second from limbic structures—through orbitomedial cortex. Outputs flow to pyramidal and diencephalic structures. Feedback inputs for monitoring and correction operate at all levels of the cycle. All prefrontal functions—planning, executive attention, working memory, decision-making, and inhibitory controls—are prospective, i.e., have a future perspective for the cycle to reach its goal. Damage to lateral prefrontal cortex impairs all of them. Orbitofrontal damage impairs the exclusionary aspect of attention and often leads to poor impulse control, excessive risk taking, unstable mood, and antisocial behavior. Medial prefrontal damage leads to poor monitoring of behavioral outcome for prevention of errors.

Our perception of the world is represented in widespread, overlapping, and interactive neuronal networks of the cerebral cortex. A majority of physiological studies on the subject have focused on oscillatory synchrony as the binding mechanism for representation and transmission of neural information. Little is known, however, about the stability of that synchrony during prolonged cognitive operations that span more than just a few seconds. The present research, in primates, investigated the dynamic patterns of oscillatory synchrony by two complementary recording methods, surface field potentials (SFPs) and near-infrared spectroscopy (NIRS). The signals were first recorded during the resting state to examine intrinsic functional connectivity. The temporal modulation of coactivation was then examined on both signals during performance of working memory (WM) tasks with long delays (memory retention epochs). In both signals, the peristimulus period exhibited characteristic features in frontal and parietal regions. Examination of SFP signals over delays lasting tens of seconds, however, revealed alternations of synchronization and desynchronization. These alternations occurred within the same frequency bands observed in the peristimulus epoch, without a specific correspondence between any definite cognitive process (e.g., WM) and synchrony within a given frequency band. What emerged instead was a correlation between the degree of SFP signal fragmentation (in time, frequency, and brain space) and the complexity and efficiency of the task being performed. In other words, the incidence and extent of SFP transitions between synchronization and desynchronization—rather than the absolute degree of synchrony—augmented in correct task performance compared with incorrect performance or in a control task without WM demand. An opposite relationship was found in NIRS: increasing task complexity induced more uniform, rather than fragmented, NIRS coactivations. These findings indicate that the particular features of neural oscillations cannot be linearly mapped to cognitive functions. Rather, information and the cognitive operations performed on it are primarily reflected in their modulations over time. The increased complexity and fragmentation of electrical frequencies in WM may reflect the activation of hierarchically diverse cognits (cognitive networks) in that condition. Conversely, the homogeneity in coherence of NIRS responses may reflect the cumulative vascular reactions that accompany that neuroelectrical proliferation of frequencies and the longer time constant of the NIRS signal. These findings are directly relevant to the mechanisms mediating cognitive processes and to physiologically based interpretations of functional brain imaging.

Objective We evaluated symptoms of anxiety (via the Hospital Anxiety and Depression Scale; HADS, HADS-A) on Stroop Color Word Test (SCWT) performances in traumatic brain injury (TBI) survivors, as compared to healthy comparison participants (HC). Method The sample consisted of 40 acute TBI survivors [ATBI; 30 normal symptoms of anxiety (NSA); 10 abnormal symptoms of anxiety (ASA)], 30 chronic TBI survivors (CTBI; 16 NSA; 14 ASA), and 50 HC’s (28 NSA; 22 ASA). All participants passed performance validity testing. The SCWT included the word (SCWT-W), color (SCWT-C), and color-word (SCWT-CW) conditions. A series of ANOVAs were used to evaluate SCWT performances. Results ANOVA revealed a main effect group on the SCWT-C, p = .011, and SCWT-CW, p = .018, with HC’s outperforming the ATBI group. Furthermore, HC outperformed both TBI groups on the SCWT-W, p = .004. We also found that the ASA outperformed the NSA group on the SCWT-W, p = .036. No interactions emerged between group and anxiety. Conclusion The HC group outperformed both TBI groups on the SCWT-W, but only the ATBI group on SCWT-C and SCWT-CW. Furthermore, we found that there were only differences between the anxiety groups on the SCWT-W. Our findings highlight that anxiety impacts HC and TBI groups differently on the SCWT.

Objective McCaul et al. (2018) recently revised the Dot Counting Test (DCT) cut-off score from ≥17 to 13.80; we evaluated the new cut-off in monolingual and bilingual traumatic brain injury survivors (TBIS) and healthy comparison participants (HCP). Method The sample consisted of 43 acute TBI [ATBI; 23 English monolinguals (EM); 11 English first language bilinguals (EFLB); and 9 English second language bilinguals (ESLB)]; 30 chronic TBI (CTBI; 13 EM; 9 EFLB; 8 ESLB), and 56 HCP (23 EM; 11 EFLB; 22 ESLB). Results An ANCOVA, controlling for age and education, revealed an interaction where ATBI-EFLB had higher E-scores than the other groups and the CTBI-EFLB had lower E-scores than the other groups. Both the conventional and proposed new cut-off (PNC) scores had different failure rates in ATBI (conventional cut-off: 9%; PNC: 28%), CTBI (conventional cut-off: 10%; PNC: 20%), and HCP (conventional cut-off: 11%; PNC: 13%). For language groups, EM (conventional cut-off: 14%; PNC: 22%), EFLB (conventional cut-off: 10%; PNC: 26%), and ESLB (conventional cut-off: 5%; PNC: 10%) demonstrated different failure rates across cut-off scores. Group differences were found with McCaul et al. (2018) cut-off, but not the conventional cut-off score. Also, chi-squared analysis revealed ATBI EFLB and EM had greater failure rates than ATBI ESLB. Conclusion Unfortunately, the new DCT cut-off score resulted in greater failure rates in TBIS. Furthermore, ATBI EM and EFLB were impacted more by the new cut offs than ATBI ESLB who learned English later in life, although the reason for this finding is unclear and requires additional study.

Objective We evaluated perceived workload (measured by the NASA Task Load Index; NASA-TLX) as related to Symbol Digit Modalities Test (SDMT) performances in monolingual and bilingual traumatic brain injury (TBI) survivors and healthy comparison participants (HC). Method The sample consisted of 28 TBI survivors (12 monolinguals & 16 bilinguals) and 50 HC (20 monolinguals & 30 bilinguals). SDMT written (SDMT-W) and SDMT oral (SDMT-O) were used to evaluate group differences. Results ANCOVA, controlling for age, revealed that the HC group outperformed the TBI group on SDMT-W, p = .001, and SDMT-O, p = .047. Furthermore, bilinguals outperformed monolinguals on SDMT-W, p = .017. On the NASA-TLX, an interaction emerged on temporal demand rating, p = .023, with TBI bilinguals reporting higher temporal demand on SDMT tasks compared to TBI monolinguals, while the HC monolingual participants reported higher temporal demands ratings compared to HC bilingual participants. Furthermore, monolingual participants showed higher levels of frustration with regard to the SDMT task compared to bilingual participants, p = .029. Conclusion Our data revealed TBI survivors underperformed on both SDMT trials compared to the HC participants. Also, bilingual participants demonstrated better SDMT-W performances compared to monolingual participants. Furthermore, our TBI bilingual sample reported themselves to be more rushed to complete the SDMT compared to monolingual TBI sample, but they were less frustrated. Meanwhile, our HC monolingual sample felt more rushed to complete the SDMT tasks compared to HC bilingual participants, but they were less frustrated. While we observed differences in workload ratings between language groups, it is unclear if language use, and/or other variables are driving these results.

Objective We examined the effects of attention/processing speed (APS) and executive functioning (EF) in Hispanic and Caucasian traumatic brain injury (TBI) survivors and healthy comparison participants (HC). Method The sample consisted of 45 HC (21 Hispanics & 24 Caucasian), 28 acute TBI (ATBI; 10 Hispanics & 18 Caucasians), and 26 chronic TBI (CTBI; 9 Hispanics; 17 Caucasians) participants. ATBI participants were tested 6 months post-injury; CTBI participants were tested 12 months or more post-injury. Symbol Digit Modalities Test (SDMT) Oral, SDMT Written, Stroop Word, Stroop Color, and Trail Making Test (TMT) part A were used to create an APS composite (APSC) score. Stroop color-word, TMT part B, Delis-Kaplan Executive Function System verbal fluency composite score, and design fluency composite score were used to create an EF composite (EFC) score. Results ANOVAs were used to evaluate group differences. Main effects were found on APSC, p = .000, with HC and CTBI outperforming the ATBI group. Also, we found the HC group outperformed both TBI groups on EFC, p = .000. Furthermore, we found differences between racial/ethnic groups, with Caucasians outperforming Hispanics on EFC performance, p = .029. No interactions were found. Conclusion Overall, HC demonstrated better EF compared to both TBI groups, but only APS compared to the ATBI group. Also, CTBI survivors demonstrated better APS abilities compared to ATBI survivors. Our findings suggest improvement in APS during the later stages of TBI recovery. Finally, Caucasians demonstrated better EF compared to Hispanics.

The pFC enables the essential human capacities for predicting future events and preadapting to them. These capacities rest on both the structure and dynamics of the human pFC. Structurally, pFC, together with posterior association cortex, is at the highest hierarchical level of cortical organization, harboring neural networks that represent complex goal-directed actions. Dynamically, pFC is at the highest level of the perception–action cycle, the circular processing loop through the cortex that interfaces the organism with the environment in the pursuit of goals. In its predictive and preadaptive roles, pFC supports cognitive functions that are critical for the temporal organization of future behavior, including planning, attentional set, working memory, decision-making, and error monitoring. These functions have a common future perspective and are dynamically intertwined in goal-directed action. They all utilize the same neural infrastructure: a vast array of widely distributed, overlapping, and interactive cortical networks of personal memory and semantic knowledge, named cognits, which are formed by synaptic reinforcement in learning and memory acquisition. From this cortex-wide reservoir of memory and knowledge, pFC generates purposeful, goal-directed actions that are preadapted to predicted future events.

The prefrontal cortex plays a critical role in the temporal organization of behavior and language within the broad neurobiological framework of the perception–action (PA) cycle, the circular processing of information that regulates the adaptation of the organism to its environment. That temporal organizing role of the prefrontal cortex is supported by three major executive functions that constitute the essential dynamic components of the cognitive control of behavior and language: (1) executive attention, (2) working memory, and (3) decision-making. The three functions are teleonomic in that they have a critical future perspective toward goal or reward. In this chapter, after discussion of the PA cycle and of the physiological role of the prefrontal cortex in it, executive attention, working memory, and decision-making are empirically placed in both cycle and cortex with the available experimental evidence.

The neural mechanisms of decision-making are understandable only in the structural and dynamic context of the perception–action (PA) cycle. The PA cycle is the biocybernetic processing of information that adapts the organism to its environment. That circular processing involves a variety of neural structures at several hierarchical levels, though with close functional interactions between them. At its lowest level, the PA cycle is largely reflex and automatic, and involves the vegetative and visceral structures of the hypothalamus and the autonomic nervous system. At intermediate levels, the cycle involves limbic structures supporting its emotional and value-assessing mechanisms. At the cortical level, under the commanding role of the prefrontal cortex, the PA cycle incorporates prefrontal cognitive components. The posterior cortex contributes to decision-making mainly information from perceptual memory and knowledge; the frontal cortex contributes mainly executive memory and knowledge. Its prefrontal sector contributes to decision-making predictive and preadaptive control through its top–down executive functions—especially attentional set, working memory, monitoring, and inhibitory control.

In the course of evolution, the prefrontal cortex develops to maximum relative mass in the human brain. That large increase in mass is attributable to the disproportionate development of connective fibers (white matter), rather than cells (gray matter). This points to connectivity as the key to the evolutionary advantage of the human prefrontal cortex. In the light of modern research, it becomes apparent that this cortex, in the human, represents the ultimate embodiment of the capability of the organism to adapt to changes in its environment; that capability rests largely on cortical connectivity. The cognitive code is a relational code, inscribed by connectivity within and between large-scale cortical networks (cognits). In this paper, it is proposed that the prefrontal cortex endows the rest of the cortex with the ability to adapt the organism to its environment in anticipation of predicted changes. This makes the brain a preadaptive organ. Therein is the reason why the executive functions of the prefrontal cortex-mainly top-down attention, working memory, preparatory set, planning, and decision making-all have a critical future dimension. Through its connections with limbic structures and other cortical regions, the prefrontal cortex imparts to the brain its power to preadapt to events in the emotional and cognitive domains.

Cognitive dynamic systems provide a broadly defined platform, whereby engineering learns from cognitive neuroscience, and by the same token, cognitive neuroscience learns from engineering. The first part of the paper is of a tutorial nature, addressing recent advances in cognitive perception and cognitive control, which are the dual of each other. The study of cognitive perception, viewed from the perspective of Bayesian inference, starts with sparse coding, well known in neuroscience. However, sparse coding could become ill-posed, particularly when the signal-to-noise ratio is low. In such situations, stability is a necessary requirement, which can only be satisfied if there is sufficient information in the observables. To satisfy this requirement, the sparse-coding algorithm is augmented by the addition of information filtering (i.e., a special case of Bayesian filtering). Accordingly, the performance of sparse coding is improved under the influence of perceptual attention. This improvement enhances the cognitive perceptor to separate relevant information from irrelevant information. Next, moving into cognitive control, viewed from the perspective of Bellman's dynamic programming, two ideas are exploited: entropic state of the perceptor, and the definition of reward as an invertible function of two entropic states, namely, the current state and its immediate past value. The net result of building on these two ideas is a modified form of Bellman's dynamic programming, and, therefore, a new reinforcement learning algorithm, which not only outperforms traditional reinforcement learning algorithms, but also offers some highly desirable properties. Among them is a linear law of computational complexity, which is the best that it could be. The second part of the paper addresses two challenging problems: first, how to mediate between cognitive control and cognitive perception and, second, how to formulate a procedure for risk control. The first problem is resolved by making use of probabilistic reasoning, a branch of probability theory, which leads into the formulation of a probabilistic reasoning machine. With this mediation in place, the conditions for overall system stability are derived, thereby confirming the probabilistic reasoning machine as the overall system stabilizer. The second challenge is risk control, which is by far the most challenging of them all: In the presence of an unexpected disturbance in the environment, risk is brought under control by mimicking the predict and preadapt function, which is considered to be the overarching function in the prefrontal cortex of the brain. To be specific, motor control is expanded by the inclusion of a new preadaptive control mechanism, which involves two different sets of actions: One set is made up of possible actions identified by the policy in the motor control. The other set involves a window of experiences (i.e., optimal actions) gained in the past. In a novel way, by exploiting these two sets, we end up with a preadaptive control mechanism in the form of a closed-loop feedback structure, which brings with it control (executive) attention.

Objective Traumatic brain injury (TBI) is associated with a number of cognitive deficits. Language factors also impact neurocognitive performance. We examined the effects of TBI and bilingualism/monolingualism on a test of attention and executive functioning (Trail Making Test; TMT). Method The sample (N = 96) consisted of 36 healthy controls (19 bilingual; 17 monolingual), 34 acute TBI participants (12 bilingual; 21 monolingual), and 27 chronic TBI participants (16 bilingual; 11 monolingual). Acute TBI participants were tested 6 months post-injury and chronic TBI participants were tested 12 months or more post-injury. 3X2 ANOVAs were conducted to determine the effect of TBI and bilingualism/monolingualism on TMT part A and B. Results Main effects were found between groups (i.e., control and TBI groups) on TMT A, p < .001, ηp² = .17 and TMT B, p < .05, ηp² = .09. Pairwise comparisons revealed a difference only between the control group and the 6-month TBI group, with the latter performing worse. Main effects were found for bilingualism/monolingualism on TMT A, p < .05, ηp² = .04 and TMT B, p < .05, ηp² = .05; monolingual participants performed better than bilingual participants. No interactions emerged. Conclusion Relative to monolinguals, bilingual participants demonstrated worse attention and executive functioning performances 6 months post-TBI; however, 12 months post-TBI, the difference was negligible.

Objective Traumatic brain injury (TBI) survivors often exhibit problems with executive function (EF). Language use can also impact EF test performances. We examined the effects of TBI and bilingualism/monolingualism on several EF tests. Method The sample (N = 94) consisted of 37 healthy controls (19 bilingual; 18 monolingual), 30 acute TBI participants (10 bilingual; 20 monolingual), and 27 chronic TBI participants (16 bilingual; 11 monolingual). Acute TBI participants were tested 6 months post-injury and chronic TBI participants were tested 12 months or more post-injury. Stroop Color-Word (SCW), Delis-Kaplan Executive Function System Letter Fluency (DKEFS-LF), Trail Making Test part B (TMT-B) and a EF global composite (EF-GC) were used to assess EF. All participants passed performance validity testing. 3X2 ANOVAs were conducted to determine the effect of TBI and bilingualism/monolingualism on EF performances. Results Main effects were found between groups (control and TBI groups) on SCW, p = .046, ηp² = .07, TMT-B, p = .042, ηp² = .07, and EF-GC, p = .005, ηp² = .13; the 6-month TBI group performed worse than controls on TMT-B and EF-GC. Main effects were found for bilingualism/ monolingualism on SCW, p = .012, ηp² = .07, and TMT-B, p = .034, ηp² = .05; monolingual participants performed better than bilingual participants. No significant interactions between TBI and language were found. Conclusion The TBI group underperformed on SCW, TMT-B, and EF-GC compared to controls; relative to monolinguals, bilinguals underperformed on the SCW and TMT-B only. In conclusion, our findings seem to suggest that monolinguals have better cognitive flexibility compared to bilinguals that result in better EF performances.

Objective Traumatic brain injury (TBI) impacts neurocognitive function. Language is also known to influence test performances. We examined the relationship between TBI and monolingualism/bilingualism on verbal and design fluency tests. Method The sample (N = 74) consisted of 33 healthy controls (18 bilingual; 15 monolingual), 15 acute TBI participants (6 bilingual; 9 monolingual), and 26 chronic TBI participants (15 bilingual; 11 monolingual). Acute TBI participants were tested 6 months post-injury and chronic TBI participants were tested 12 months or more post-injury. The Delis-Kaplan Executive Function System Letter Fluency (DKEFS-LF), Category Fluency (DKEFS-CF), Category Switching Fluency (DKEFS-CSF), and global verbal fluency composite (DKEFS-GVF) scores assessed verbal fluency; DKEFS fill-dots (DKEFS-FD), empty dots (DFEFS-ED), dot switching (DKEFS-DS), and global design fluency composite (DKEFS-GDF) scores assessed design fluency; and global verbal and non-verbal fluency composite (DKEFS-GF) assessed overall fluency. 3X2 ANOVAs were conducted to evaluate the effect of monolingualism/bilingualism on fluency performance in TBI and controls. Results The groups (control and TBI groups) differed for DKEFS-LF, p = .048, ηp² = .09, DKEFS-CF, p = .000, ηp² = .21, DKEFS-GVF, p = .004, ηp² = .15, DKEFS-ED, p = .008, ηp² = .13, DKEFS-GF, p = .001, ηp² = .20, with controls outperforming TBI groups on the DKEFS-CF, DKEFS-GVF, and DKEFS-GF. Furthermore, controls outperformed acute TBI participants on the DKEFS-LF and DKEFS-ED. Main effects were found for bilingualism/monolingualism on DKEFS-CF, p = .035, ηp² = .06, with bilinguals outperforming monolinguals. No interactions were found. Conclusion The TBI group had poor verbal and design fluency in contrast controls. Unexpectedly, bilinguals outperformed monolinguals on a task of verbal category fluency. Revealing that in the present study bilinguals have better semantic verbal fluency abilities.

Objective Traumatic brain injury (TBI) survivors exhibit cognitive deficits. Language factors can also influence neurocognitive performance. We examined the effects of TBI and bilingualism/monolingualism on a test of attention and cognitive speed (i.e., Symbol Digit Modalities Test; SDMT). Method The sample (N = 98) consisted of 37 controls (19 bilingual; 18 monolingual), 34 acute TBI participants (12 bilingual; 22 monolingual), and 27 chronic TBI participants (16 bilingual; 11 monolingual). Acute TBI participants were tested 6 months post-injury; chronic TBI participants were tested 12 months or more post-injury. All participants passed performance validity testing. 3X2 ANOVAs were conducted to determine the effect of TBI and language on SDMT written and oral performance. Results A main effect was found between groups (control and TBI groups) on SDMT written, p < .001, ηp² = .19 and SDMT oral p < .001, ηp² = .16. Pairwise comparisons revealed a difference between the control group and TBI groups, with TBI groups performing worse. A main effect for bilingualism/monolingualism was not found; interaction effects emerged between TBI and bilingualism/monolingualism on SDMT written, p < .05, ηp² = .07 and SDMT oral p < .05, ηp² = .07. Conclusion TBI groups performed worse than controls on the SDMT. Relative to monolinguals with TBI, our findings suggest better cognitive recovery of verbal attention and cognitive speed in bilingual TBI participants.

Objective Traumatic brain injury (TBI) affects neurocognition. Speaking multiple languages can also influence cognitive test performances. We examined the relationship between TBI and monolingualism/bilingualism on a task of attention and response inhibition (Stroop Color Word Test; SCWT). Method The sample (N = 96) consisted of 37 healthy controls (19 bilingual; 18 monolingual), 32 acute TBI participants (12 bilingual; 20 monolingual), and 27 chronic TBI participants (16 bilingual; 11 monolingual). Acute TBI participants were tested 6 months post-injury and chronic TBI participants were tested 12 months or more post-injury. The SCWT included the word (SCWT-W), color (SCWT-C), and color-word interference (SCWT-I) conditions. All participants passed performance validity testing. 3X2 ANOVAs were conducted to examine the relationship between TBI and monolingualism/bilingualism on SCWT performances. Results Group effects (control and TBI groups) were found for all Stroop measures. We found main effects of TBI on SCWT-W, p = .013, ηp² = .09, SCWT-C, p = .001, ηp² = .14, and SCWT-I, p = .022, ηp² = .08, with the controls outperforming acute TBI survivors on SCWT-I, chronic TBI survivors on SCWT-W, and both TBI groups on SCWT-C. We also observed main effects of language for SCWT-C, p = .012, ηp² = .07, and SCWT-I, p = .003, ηp² = .09, with the monolinguals outperforming bilinguals on SCWT-C and SCWT-I. However, no significant interactions between TBI and language were found. Conclusion As expected, the control group outperformed TBI survivors on the SCWT. Monolinguals outperformed bilinguals on all Stroop measures except SCWT-W condition. Our findings seem to suggest that monolingual speakers may have better attention and response inhibition abilities that resulted in better SCWT performance.

Objective The Boston Naming Test (BNT) is a lexical-retrieval task. It has been documented that those with a history of traumatic brain injury (TBI) have reduced performance on the BNT. Bilingualism is also known to impact BNT performances. We examined the relationship of TBI and bilingualism/monolingualism on BNT performances. Method The sample (N = 95) consisted of 36 healthy controls (19 bilingual; 17 monolingual), 32 acute TBI participants (12 bilingual; 20 monolingual), and 27 chronic TBI participants (16 bilingual; 11 monolingual). Acute TBI participants were tested 6 months post-injury and chronic TBI participants were tested 12 months or more post-injury. All participants passed performance validity testing. A 3X2 ANOVA was conducted to determine the effect of TBI and bilingualism/monolingualism on BNT performance. Results A main effect was found for group (i.e., control, 6 month TBI, and 12 month TBI), p < .001, ηp² = .21. Pairwise comparisons revealed that acute TBI participants performed worse than the control and chronic TBI groups. A main effect for bilingualism/ monolingualism was found, p < .001, ηp² = .14; monolinguals performed better on the BNT. No interactions were found between TBI and bilingualism/monolingualism. Conclusions BNT performance improves overtime in TBI and the pattern of improvement post-TBI is not statistically different between bilingual/monolingual groups. Relative to monolinguals, bilingual participants demonstrated worse BNT performance.

Converging evidence from humans and nonhuman primates is obliging us to abandon conventional models in favor of a radically different, distributed-network paradigm of cortical memory. Central to the new paradigm is the concept of memory network or cognit—that is, a memory or an item of knowledge defined by a pattern of connections between neuron populations associated by experience. Cognits are hierarchically organized in terms of semantic abstraction and complexity. Complex cognits link neurons in noncontiguous cortical areas of prefrontal and posterior association cortex. Cognits overlap and interconnect profusely, even across hierarchical levels (heterarchically), whereby a neuron can be part of many memory networks and thus many memories or items of knowledge.

This study explores the cortical cell dynamics of unimodal and cross-modal working memory (WM). Neuronal activity was recorded from parietal areas of monkeys performing delayed match-to-sample tasks with tactile or visual samples. Tactile memoranda (haptic samples) consisted of rods with differing surface features (texture or orientation of ridges) perceived by active touch. Visual memoranda (icons) consisted of striped patterns of differing orientation. In a haptic-haptic task, the animal had to retain through a period of delay the surface feature of the sample rod to select a rod that matched it. In a visual-haptic task, the animal had to retain the icon for the haptic choice of a rod with ridges of the same orientation as the icon's stripes. Units in all areas responded with firing change to one or more task events. Also in all areas, cells responded differently to different sample memoranda. Differential sample coherent firing was present in most areas during the memory period (delay). It is concluded that neurons in somatosensory and association areas of parietal cortex participate in broad networks that represent various task events and stimuli (auditory, motor, proprioceptive, tactile, and visual). Neurons in the same networks take part in retaining in WM the memorandum for each trial, whether it is encoded haptically or visually. The VH association by parietal cells in WM is analogous to the auditory-visual association previously observed in prefrontal cortex. Both illustrate the capacity of cortical neurons to associate sensory information across time and across modalities in accord with the rules of a behavioral task.

Persistent elevated neuronal activity has been identified as the neuronal correlate of working memory. It is generally assumed in the literature and in computational and theoretical models of working memory that memory-cell activity is stable and replicable; however, this assumption may be an artifact of the averaging of data collected across trials, and needs experimental verification. In this study, we introduce a classification scheme to characterize the firing frequency trends of cells recorded from the cortex of monkeys during performance of working memory tasks. We examine the frequency statistics and variability of firing during baseline and memory periods. We also study the behavior of cells on individual trials and across trials, and explore the stability of cellular firing during the memory period. We find that cells from different firing-trend classes possess markedly different statistics. We also find that individual cells show substantial variability in their firing behavior across trials, and that firing frequency also varies markedly over the course of a single trial. Finally, the average frequency distribution is wider, the magnitude of the frequency increases from baseline to memory smaller, and the magnitude of frequency decreases larger than is generally assumed. These results may serve as a guide in the evaluation of current theories of the cortical mechanisms of working memory.

Considerable progress has been made in neuroimaging methodology, including improved ways to quantify volumes of gray and white matter, by tractography and diffusion tensor imaging, and functional methods to correlate cortical activity (blood oxygen level-dependent imaging) with cognitive function (increased spatial and temporal resolution). A default network is defined at rest; this spans several cortical areas, including prefrontal cortex, and oscillates at extremely slow frequency. Planning or imagining a series of goal-directed actions activates rostral prefrontal cortex. In attention to sensory or executive information, the prefrontal cortex activates cortical cognitive networks that are expected to process that information. In working memory, the prefrontal cortex is coactivated with posterior cortical networks that engage with that cortex in the cross-temporal integration of information for a successful perception–action cycle. Volumetric deficits in prefrontal gray and/or white matter are found in attention deficit/hyperactivity disorder, schizophrenia, obsessive–compulsive disorder, depression, and dementia.

This chapter aims to present a conceptual model of prefrontal function that, by deductive and synthetic reasoning, accommodates the empirical evidence discussed in previous chapters of the book. The model is essentially based on four general propositions for which there is now overwhelming empirical support: the entirety of the cortex of the frontal lobe is devoted to the representation and production of action at all levels of biological complexity; the neuronal substrate for the production of any action is identical to the substrate for its representation; that substrate is organized hierarchically, with the most elementary actions at low levels of the hierarchy, in orbitofrontal and motor cortex, and the most complex and abstract actions in lateral prefrontal cortex; frontal-lobe functions are also organized hierarchically, with simpler functions nested within, and serving, more global functions. The three principal executive functions of the prefrontal cortex, at the service of the organization and implementation of action, are executive attention, planning, and decision-making. Executive attention is the first major executive function of the prefrontal cortex, and has three aspects or sub-functions: preparatory set, working memory, and control of interference. Planning is the second major executive function of the prefrontal cortex, as it is essential for the formulation and execution of novel plans or structures (gestalts) of goal-directed behavior. Decision-making is the third major executive function of the prefrontal cortex. The orbitomedial prefrontal cortex plays a crucial role in emotional behavior.

This chapter focuses on the anatomy and developmental neurobiology of the prefrontal cortex. It begins with a discussion of issues related to the phylogenetic development and comparative anatomy of the neocortex of the frontal lobe. The chapter also deals with its ontogenetic development and the morphological changes it undergoes as a result of aging. The ontogenetic development of the prefrontal cortex reflects its phylogeny. Orbitomedial areas mature earlier than lateral ones. In early life, neurons in the prefrontal cortex proliferate migrate to their ultimate cortical destination, and experience growth according to the timetable that prevails throughout the neocortex. The chapter then deals with the anatomy and microscopic architecture of the prefrontal cortex in the adult organism. Different regions of the prefrontal cortex have different sets of reciprocal connections. An overview of the afferent and efferent connections of the prefrontal cortex in several species is also provided in the chapter. This overview of connectivity of the prefrontal cortex, arguably the most richly connected of all cortical regions, opens the way to subsequent chapters, where connectivity is found to be the key to all its functions.

The prevalent concept in modular models is that there are discrete cortical domains dedicated more or less exclusively to such cognitive functions as visual discrimination, language, spatial attention, face recognition, motor programming, memory retrieval, and working memory. Most of these models have failed or languished for lack of conclusive evidence. In their stead, network models are emerging as more suitable and productive alternatives. Network models are predicated on the basic tenet that cognitive representations consist of widely distributed networks of cortical neurons. Cognitive functions, namely perception, attention, memory, language, and intelligence, consist of neural transactions within and between these networks. The present model postulates that memory and knowledge are represented by distributed, interactive, and overlapping networks of neurons in association cortex. Such networks, named cognits, constitute the basic units of memory or knowledge. The association cortex of posterior-post-rolandic-regions contains perceptual cognits: cognitive networks made of neurons associated by information acquired through the senses. Conversely, frontal association cortex contains executive cognits, made of neurons associated by information related to action. In both posterior and frontal cortex, cognits are hierarchically organized. At the bottom of that organization-that is, in parasensory and premotor cortex-cognits are small and relatively simple, representing simple percepts or motor acts. At the top of the organization-in temporo-parietal and prefrontal cortex-cognits are wider and represent complex and abstract information of perceptual or executive character. Posterior and frontal networks are associated by long reciprocal cortico-cortical connections. These connections support the dynamics of the perception-action cycle in sequential behavior, speech, and reasoning.

We have studied a neurodynamic model of cross-modal and cross-temporal associations. We show that a network of integrate-and-fire neurons can generate spiking activity with realistic dynamics during the delay period of a paired associates task. In particular, the activity of the model resembles reported data from single-cell recordings in the prefrontal cortex.

We describe the use of near-infrared spectroscopy (NIRS) as a suitable means of assessing hemodynamic changes in the cerebral cortex of awake and behaving monkeys. NIRS can be applied to animals performing cognitive tasks in conjunction with electrophysiological methods, thus offering the possibility of investigating cortical neurovascular coupling in cognition. Because it imposes fewer constraints on behavior than fMRI, NIRS appears more practical than fMRI for certain studies of cognitive neuroscience on the primate cortex. In the present study, NIRS and field potential signals were simultaneously recorded from the association cortex (posterior parietal and prefrontal) of monkeys performing two delay tasks, one spatial and the other non-spatial. Working memory was accompanied by an increase in oxygenated hemoglobin mirrored by a decrease in deoxygenated hemoglobin. Both the trends and the amplitudes of these changes differed by task and by area. Field potential records revealed slow negative potentials that preceded the task trials and persisted during their memory period. The negativity during that period was greater in prefrontal than in parietal cortex. Between tasks, the potential differences were less pronounced than the hemodynamic differences. The present feasibility study lays the groundwork for future correlative studies of cognitive function and neurovascular coupling in the primate.

1Instituto Cajal (CSIC), Madrid, Spain; 2Department of Physiology and Pharmacology, Vision, Touch and Hearing Research Centre, School of Biomedical Sciences, The University of Queensland, Brisbane, Australia; 3Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan; 4Neuropsychiatric Institute and Brain Research Institute, UCLA School of Medicine Los Angeles, California, USA; 5Department of Molecular Biology, Princeton University, Princeton, New Jersey, USA; 6Fishberg Research Center for Neurobiology, Kastor Neurobiology of Aging Laboratories, and Advanced Imaging Program, Mount Sinai School of Medicine, New York, USA; 7Division of Cerebral Circuitry, National Institute for Physiological Sciences, Okazaki, Japan; 8Institute of Neuroinformatics, University Zurich and ETH Zurich, Switzerland; 9Laboratory for Cortical Organization and Systematics, RIKEN Brain Science Institute, Wako-shi, Saitama, Japan; 10Department of Pharmacology, The School of Pharmacy, London University, UK; 11Department of Morphology, Faculty of Health Sciences and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer Sheva, Israel; 12Department of Biological Sciences, Columbia University, New York, USA

In phylogeny as in ontogeny, the association cortex of the frontal lobe, also known as the prefrontal cortex, is a late-developing region of the neocortex. It is also one of the cortical regions to undergo the greatest expansion in the course of both evolution and individual maturation. In the human adult, the prefrontal cortex constitutes as much as nearly one-third of the totality of the neocortex. The protracted, relatively large, development of the prefrontal cortex is manifest in gross morphology as well as fine structure. In the developing individual, its late maturation is made most apparent by the late myelination of its axonal connections. This and other indices of morphological development of the prefrontal cortex correlate with the development of cognitive functions that neuropsychological studies in animals and humans have ascribed to this cortex. In broad outline, the ventromedial areas of the prefrontal cortex, which with respect to other prefrontal areas develop relatively early, are involved in the expression and control of emotional and instinctual behaviors. On the other hand, the late maturing areas of the lateral prefrontal convexity are principally involved in higher executive functions. The most general executive function of the lateral prefrontal cortex is the temporal organization of goal-directed actions in the domains of behavior, cognition, and language. In all three domains, that global function is supported by a fundamental role of the lateral prefrontal cortex in temporal integration, that is, the integration of temporally discontinuous percepts and neural inputs into coherent structures of action. Temporal integration is in turn served by at least three cognitive functions of somewhat different prefrontal topography: working memory, preparatory set, and inhibitory control. These functions engage the prefrontal cortex in interactive cooperation with other neocortical regions. The development of language epitomizes the development of temporal integrative cognitive functions and their underlying neural substrate, notably the lateral prefrontal cortex and other late-developing cortical regions.

Previous studies have shown that neurons of monkey dorsolateral prefrontal cortex (DLPFC) integrate information across modalities and maintain it throughout the delay period of working-memory (WM) tasks. However, the mechanisms of this temporal integration in the DLPFC are still poorly understood. In the present study, to further elucidate the role of the DLPFC in crossmodal WM, we trained monkeys to perform visuo–haptic (VH) crossmodal and haptic–haptic (HH) unimodal WM tasks. The neuronal activity recorded in the DLPFC in the delay period of both tasks indicates that the early-delay differential activity probably is related to the encoding of sample information with different strengths depending on task modality, that the late-delay differential activity reflects the associated (modality-independent) action component of haptic choice in both tasks (that is, the anticipation of the behavioral choice and/or active recall and maintenance of sample information for subsequent action), and that the sustained whole-delay differential activity likely bridges and integrates the sensory and action components. In addition, the VH late-delay differential activity was significantly diminished when the haptic choice was not required. Taken together, the results show that, in addition to the whole-delay differential activity, DLPFC neurons also show early- and late-delay differential activities. These previously unidentified findings indicate that DLPFC is capable of (i) holding the coded sample information (e.g., visual or tactile information) in the early-delay activity, (ii) retrieving the abstract information (orientations) of the sample (whether the sample has been haptic or visual) and holding it in the late-delay activity, and (iii) preparing for behavioral choice acting on that abstract information.

Traumatic brain injury (TBI) is associated with deficits in memory for the content of completed activities. However, TBI groups have shown variable memory for the temporal order of activities. We sought to clarify the conditions under which temporal order memory for activities is intact following TBI. Additionally, we evaluated activity source memory and the relationship between activity memory and functional outcome in TBI participants. Thus, we completed a study of activity memory with 18 severe TBI survivors and 18 healthy age- and education-matched comparison participants. Both groups performed eight activities and observed eight activities that were fashioned after routine daily tasks. Incidental encoding conditions for activities were utilized. The activities were drawn from two counterbalanced lists, and both performance and observation were randomly determined and interspersed. After all of the activities were completed, content memory (recall and recognition), source memory (conditional source identification), and temporal order memory (correlation between order reconstruction and actual order) for the activities were assessed. Functional ability was assessed via the Community Integration Questionnaire (CIQ). In terms of content memory, TBI participants recalled and recognized fewer activities than comparison participants. Recognition of performed and observed activities was strongly associated with social integration on the CIQ. There were no between- or within-group differences in temporal order or source memory, although source memory performances were near ceiling. The findings were interpreted as suggesting that temporal order memory following TBI is intact under conditions of both purposeful activity completion and incidental encoding, and that activity memory is related to functional outcomes following TBI.

I wish to thank Eric Kandel, James McGaugh, Earl Miller, and Thomas O'Dell for their comments on the manuscript.

The prefrontal cortex is one of the latest regions of the neocortex to develop, in both phylogeny and ontogeny. In the primate, the prefrontal cortex is anatomically divided into three major sectors: medial, orbital (or inferior), and dorsolateral. The dorsolateral sector is the association cortex of the convexity of the frontal lobe. Phylogenetically and ontogenetically, this part of the prefrontal cortex is the one to develop last and most. It is the neural substrate of the higher cognitive functions that reach their maximum development in the human brain. The most general and distinctive function of the dorsolateral prefrontal cortex is the temporal organization of goal-directed actions. In the human, this role extends to the domains of speech and reasoning. Two temporally symmetrical and mutually complementary cognitive functions—one retrospective and the other prospective—support that general prefrontal function of temporal organization: (1) active short-term memory, also called working memory; (2) prospective or preparatory set. The dorsolateral prefrontal cortex interacts with other cortical and subcortical structures in those two time-bridging functions at the basis of the temporal organization of behavior.

This chapter presents a conceptual model of the representational and executive functions of the cortex of the frontal lobe derived from empirical evidence obtained principally in the monkey. According to this model, the neuronal networks of the frontal lobe that represent motor or executive memories are probably the same networks that cooperate with other cerebral structures in the temporal organization of behavior. The prefrontal cortex, at the top of the perception-action cycle, plays a critical role in the mediation of contingencies of action across time, an essential aspect of the temporal organization of behavior. That role of cross-temporal mediation is based on the interplay of two short-term cognitive functions: one retrospective, of short-term memory or sensory working memory, and the other prospective, of attentive set (or motor working memory). Both appear represented in the neuronal populations of dorsolateral prefrontal cortex. At least one of the mechanisms for the retention of working memory of either kind seems to be the reentry of excitability through recurrent cortical circuits. With those two complementary and temporally symmetrical cognitive functions of active memory for the sensory past and for the motor future, the prefrontal cortex secures the temporal closure at the top of the perception-action cycle.

The cortex of the frontal lobe reaches maximum phylogenetic development in the brain of the human. It is cortex devoted to the organization of action in all neurobiological and cognitive domains - skeletal movement, eye movement, speech and logical reasoning. Thus the frontal cortex may be called 'motor cortex' in the widest sense. The association cortex of the frontal lobe, commonly called prefrontal cortex, is in charge of the temporal organization of behaviour, speech and thinking. Prefrontal lesions frequently lead to disorders of temporal organization, especially in thinking and the spoken language. The prefrontal cortex serves temporal organization by coordinating three cognitive operations that are essential for the formation of 'gestalts' in the time domain: (i) preparatory set; (ii) working memory; and (iii) inhibitory control of interference. Temporal organization is disturbed in the schizophrenic patient, probably because of a functional disorder of the connectivity between the prefrontal cortex and other cortical areas, as well as limbic and striatal structures (a 'disconnection syndrome').