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Poor short-term memory (STM) capacity in individuals with dyslexia (IDDs) and enhanced STM capacity in musicians are well documented, yet their causes are disputed. Previous studies also found poor use of stimuli statistics by IDDs and enhanced use by musicians. We hypothesized that these observations are functionally related, as follows: Enhanced sensitivity to statistics facilitates musicians' benefit from each exposure, and reduced sensitivity to statistics hinders IDDs' benefit. Thus, larger group differences are expected for larger exposure: STM capacity, which is sensitive to item familiarity, will thus be larger among musicians, and smaller among IDDS, particularly for high-frequency items. Testing this hypothesis using syllable span, we found that musicians' advantage and IDDs' difficulty were indeed larger for high-frequency syllables than for low-frequency ones. By contrast, benefits from sequence repetition did not differ between musicians, controls and IDDs, suggesting that online sequence learning is based on a different mechanism. To test this dissociation we recruited, in addition to native Hebrew speakers, native English speakers, matched to the Hebrew-speaking controls. Their spans for high-frequency syllables in Hebrew, which do not have high frequency in English, were small - as expected from reduced exposure to these syllables. Yet, their benefit from sequence repetition was similar to that of the three Hebrew-speaking groups. Taken together, these experiments suggest that different sensitivities to item frequency explain some of the population-related variability in STM tasks. By contrast, benefits from sequence repetition do not depend on item familiarity, and do not differ between groups., Highlights • Study on 4 groups: Hebrew/English speakers, individuals with dyslexia, musicians. • Individuals with dyslexia benefit from syllable frequency less than controls. • Musicians benefit from syllable frequency more than controls. • Benefits from sequence repetition are stable across different populations.

Neuroimaging studies suggest that the increment of the cognitive load associated with a specific task may induce the recruitment of a more bilateral brain network. In most studies, however, task demand has been manipulated in a static and pre-specified way, regardless of individual cognitive resources. Here we implemented a new paradigm based on a pre-experimental assessment to set up subject-specific levels of task demand and applied tDCS (transcranial direct current stimulation) to assess each hemisphere involvement in task performance. 24 young participants performed a digit span backward (DSB, complex cognitive function) and a paced finger tapping task (pFT, basic motor function) at 3 levels of subject-specific task demand ("low" 5/5 correct answers, "medium" 3/5, "high" 1/5). Anodal tDCS (20min, 1.5mA) was delivered through a target electrode (5 × 5cm) positioned to stimulate both the inferior frontal gyrus and the primary motor area over left and right hemisphere and in sham condition in three different days. A 3 (left, right, sham) × 3 (low, medium, high) mixed-model with random intercept for subjects was run with R software. As expected, in both tasks accuracy decreased with the increment of subject-specific task demand. Moreover, a significant interaction between type of stimulation and subject-specific task demand was found for the reaction times recorded during the DSB and for the accuracy in the pFT: in the most demanding conditions, right anodal tDCS significantly interfered with behavioural performance. Our results suggest that hemispheric lateralization is modulated by the subject-specific level of task demand and this modulation is not task-specific.

Metaphoric language is one of the most common expressions of creative cognition in everyday life. However, the cognitive mechanisms underlying metaphor generation remain largely unexplained. In this study, we aimed to investigate the relationship between various cognitive functions and both novel and conventional metaphor generation. Ninety-five undergraduate students were administered a metaphor generation task that assesses novel and conventional metaphor generation, along with a battery of different cognitive measures: vocabulary; divergent thinking (Tel Aviv Creativity Test), working memory (WM) via digit span tests, executive functions (EFs) using the Behavioral Rating Inventory of Executive Function (BRIEF) questionnaire, and selective attention (lateralized global-local digit task). Results of a path analysis indicated that - whereas only selective attention contributed to conventional metaphor generation - selective attention, divergent thinking, and EFs contributed to novel metaphor generation beyond vocabulary and WM. Thus, the results indicate that although both novel and conventional metaphor generation are linked to attentional resources and inhibitory control, the greater creativity inherent in novel metaphor generation appears to reflect a more complex set of cognitive processes than conventional metaphor generation.

Although research shows that working memory improves during early childhood, it remains unclear how the fronto-parietal network of cortical regions, known to support this ability in adults, relates to changes in young children. Measures of cortical thickness may be useful in investigating this association as they reflect age-related differences in gray matter and have been proposed to support age-related improvements in other cognitive abilities, but have only sparingly been tested empirically in early childhood. The present study sought to investigate relations between cortical thickness and performance on a digit span task in 200 4- to 8-year-old children using both a priori defined regions of interest related to working memory (superior frontal cortex, middle frontal cortex, anterior cingulate cortex, superior parietal cortex) and whole brain analyses. Results indicated a significant association between cortical thickness in each a priori defined fronto-parietal region and performance on digit span, such that those with a thinner cortex recalled more items than those with a thicker cortex. Similar regions emerged from the whole brain analyses, as did several other regions not typically included in the fronto-parietal network. Results of a mediation analysis indicated that age-related differences in behavior were partially explained by variations in thickness of anterior cingulate cortex, suggesting a potentially important role for this structure during early childhood. Overall, these results suggest that in children as young as 4 years of age there are associations between working memory abilities and thickness in cortical areas known to support working memory in adults.

International audience; Although the development of executive functions has been extensively investigated at a neurofunctional level, studies of the structural relationships between executive functions and brain anatomy are still scarce. Based on our previous meta-analysis of functional neuroimaging studies examining executive functions in children (Houdé, Rossi, Lubin, and Joliot, (2010). Developmental Science, 13, 876-885), we investigated six a priori regions of interest: the left anterior insular cortex (AIC), the left and the right supplementary motor areas, the right middle and superior frontal gyri, and the left precentral gyrus. Structural magnetic resonance imaging scans were acquired from 22 to 10-year-old children. Local gray matter volumes, assessed automatically using a standard voxel-based morphometry approach, were correlated with executive and storage working memory capacities evaluated using backward and forward digit span tasks, respectively. We found an association between smaller gray matter volume-i.e., an index of neural maturation-in the left AIC and high backward memory span while gray matter volumes in the a priori selected regions of interest were not linked with forward memory span. These results were corroborated by a whole-brain a priori free analysis that revealed a significant negative correlation in the frontal and prefrontal regions, including the left AIC, with the backward memory span, and in the right inferior parietal lobe, with the forward memory span. Taken together, these results suggest a distinct and specific association between regional gray matter volume and the executive component vs. the storage component of working memory. Moreover, they support a key role for the AIC in the executive network of children.

Despite the traditional view that damage to the hippocampus and/or surrounding areas of the medial temporal lobe (MTL) does not impair short-term or working memory (WM), recent research has shown MTL amnesics to be impaired on WM tasks that require maintaining a small amount of information over brief retention intervals (e.g., maintenance of a single face for one second). However, the types of tasks that have demonstrated WM impairments in amnesia tend to have involved novel stimuli. We hypothesized that WM may be impaired in amnesia for tasks that require maintaining novel information, but may be preserved for more familiar material, particularly if the material can be easily rehearsed. To test this hypothesis, patient HC, a 22-year-old developmental amnesic with relatively preserved semantic memory and 20 age and education matched controls performed a delayed match-to-sample task that required maintaining a single famous or non-famous face for 1–8 s, digit span and reading span tasks, and a modified Brown–Peterson task that required maintaining a single high- or low-frequency word or a non-word for 4–8 s. HC's performance was impaired for non-famous faces but preserved for famous faces, impaired for the reading span task but preserved for digit span, and it was impaired for non-words and unfamiliar low-frequency words but preserved for familiar words. These results support the hypothesis that an intact hippocampus is necessary for maintaining a single novel stimulus in WM. However, stimulus familiarity and rehearsal support WM via cortical regions independent of the MTL.

Patients with probable Alzheimer's disease (AD) and the amnesic form of mild cognitive impairment (aMCI) often demonstrate several types of neuropsychological deficits. These deficits are often related to cortical atrophy, induced by neuronal degradation. The purpose of this study is to investigate whether different anatomic patterns of cortical atrophy are associated with specific neuropsychological deficits. The participants were 170 patients with AD and 99 patients with aMCI. All participants underwent the Seoul Neuropsychological Screening Battery (SNSB), which includes tests that assess attention, language, visuospatial functions, verbal and visual memory, and frontal/executive functions. Cortical atrophy (thinning) was quantified by measuring the thickness of the cortical mantle across the entire brain using automated, three-dimensional magnetic resonance imaging. The relationship between cortical thickness and neuropsychological performance was analysed using stepwise multiple linear regression analyses. These analyses (corrected P

The aim of the present study is to investigate short-term memory and working memory deficits in aphasics in relation to the severity of their language impairment. Fifty-eight aphasic patients participated in this study. Based on language assessment, an aphasia score was calculated for each patient. Memory was assessed in two modalities, verbal and spatial. Mean scores for all memory tasks were lower than normal. Aphasia score was significantly correlated with performance on all memory tasks. Correlation coefficients for short-term memory and working memory were approximately of the same magnitude. According to our findings, severity of aphasia is related with both verbal and spatial memory deficits. Moreover, while aphasia score correlated with lower scores in both short-term memory and working memory tasks, the lack of substantial difference between corresponding correlation coefficients suggests a possible primary deficit in information retention rather than impairment in working memory.

Objective Patients with cerebellar stroke are impaired in motor skill acquisition and cognitive/executive performance. The aim was to test whether skill acquisition in cerebellar patients is influenced by executive demands such as the intermittent exercise of a conflicting motor task. Methods Patients with cerebellar stroke and healthy controls were tested in two serial reaction time experiments. In Experiment 1, participants performed practice runs (always same sequence) and interference runs (new sequence for each run) in a strictly alternating fashion. In Experiment 2, participants rested between successive practice runs; the duration of rests was adapted to the duration of interference runs in the other experiment. Participants of Experiment 1 were also tested for cognitive–executive functions (Wisconsin Card Sort, Word Fluency, Trail Making, Digit Span backwards). Results (1) Patients in Experiment 1, although always slower than controls, acquired motor skills in the first run before interference but in contrast to controls failed to improve their performance in subsequent runs. (2) Patients in Experiment 2 improved their performance consistently over several runs. (3) Patients of Experiment 1 were worse than controls in several cognitive–executive functions; however, these deficits did not correlate with the degree of interference in motor skill acquisition. Interpretation Simple movement coordination and higher order context-related movement organisation are separate cerebellar functions. In cerebellar patients, impaired movement coordination is associated with generally slower reaction times whereas organisational deficits are associated with a specific impairment to change between motor sets. Motor-executive functions responsible for the latter impairment might be independent from cognitive–executive functions.

The underlying neural mechanisms of developmental dyscalculia (DD) are still far from being clearly understood. Even the behavioral processes that generate or influence this heterogeneous disorder are a matter of controversy. To date, the few studies examining functional brain activation in children with DD mainly focus on number and counting related tasks, whereas studies on more general cognitive domains that are involved in arithmetical development, such as working memory are virtually absent. There are several studies showing a close relationship between DD and spatial working memory [Camos, V. (2008). Low working memory capacity impedes both efficiency and learning of number transcoding in children. Journal of Experimental Child Psychology, 99(1), 37-57; McLean, J. F., & Hitch, G. J. (1999). Working memory impairments in children with specific arithmetic learning difficulties. Journal of Experimental Child Psychology, 74(3), 240-260; Rosselli, M., Matute, E., Pinto, N., & Ardila, A. (2006). Memory abilities in children with subtypes of dyscalculia. Developmental Neuropsychology, 30(3), 801-818; Siegel, L. S., & Ryan, E. B. (1989). The development of working memory in normally achieving and subtypes of learning disabled children. Child Development, 60(4), 973-980]. The relationship between these two mechanisms is still matter of debate, but this study follows the assumption that poor spatial working memory capacity may hinder the acquisition of spatial number representations in children with DD [Geary, D. C. (1993). Mathematical disabilities: Cognitive, neuropsychological, and genetic components. Psychological Bulletin, 114(2), 345-362; von Aster, M., & Shalev, R. S. (2007). Number development and developmental dyscalculia. Developmental Medicine and Child Neurology, 49(11), 868-873]. Using functional MRI the current study compares brain activity associated with spatial working memory processes in 8-10-year-old children with DD and normally achieving controls. Both groups showed significant spatial working memory related activity in a network including occipital and parietal regions. Children with DD showed weaker neural activation compared to the control group during a spatial working memory task in the right intraparietal sulcus (IPS), the right insula and the right inferior frontal lobe. Performance tests outside the scanner showed impaired working memory proficiency in children with DD. Bringing behavioral performance and neural activity together we found significant correlations of right IPS activity with performance on the verbal digit span forward and the spatial Corsi Block Tapping test. Our findings demonstrate for the first time an involvement of spatial working memory processes in the neural underpinnings of DD. These poor spatial working memory processes may inhibit the formation of spatial number representations (mental numberline) as well as the storage and retrieval of arithmetical facts.

Congenitally blind individuals have been found to show superior performance in perceptual and memory tasks. In the present study, we asked whether superior stimulus encoding could account for performance in memory tasks. We characterized the performance of a group of congenitally blind individuals on a series of auditory, memory and executive cognitive tasks and compared their performance to that of sighted controls matched for age, education and musical training. As expected, we found superior verbal spans among congenitally blind individuals. Moreover, we found superior speech perception, measured by resilience to noise, and superior auditory frequency discrimination. However, when memory span was measured under conditions of equivalent speech perception, by adjusting the signal to noise ratio for each individual to the same level of perceptual difficulty (80% correct), the advantage in memory span was completely eliminated. Moreover, blind individuals did not possess any advantage in cognitive executive functions, such as manipulation of items in memory and math abilities. We propose that the short-term memory advantage of blind individuals results from better stimulus encoding, rather than from superiority at subsequent processing stages.

Behavioral studies indicate deficits in phonological working memory (WM) and executive functioning in dyslexics. However, little is known about the underlying functional neuroanatomy. In the present study, neural correlates of WM in adolescents and young adults with dyslexia were investigated using event-related functional magnetic resonance imaging (fMRI) and a parametric verbal WM task which required the manipulation of verbal material. Dyslexics were not significantly slower than controls; however, they were less accurate with the highest WM demand. The functional analysis excluded incorrectly performed and omitted trials, thus controlling for potential activation confounds. Compared with control subjects, both increased and decreased activation of the prefrontal cortex were found in the dyslexic group. Dyslexics showed significantly more activation than controls with increasing WM demand in the left superior frontal gyrus (BA 8), as well as in the inferior frontal gyrus including Broca's area (BA 44) and its right homologue. Less activation was found in the middle frontal gyrus (BA 6) and in the superior parietal cortex (BA 7). A positive correlation between activation of prefrontal regions and verbal WM performance (as measured by digit span backwards) was found only in the dyslexic group. Accuracy deficits at the highest cognitive demand during the verbal WM task and the digit span backwards suggest that manipulation rather than maintenance is selectively impaired in dyslexics. The fMRI data provide further evidence for functional differences in cortical regions associated with language processing and executive function in subjects with dyslexia.

This study explores differences in cognitive outcome after a standard resection (SR) or tailored (TR) in 100 patients with left temporal lobe epilepsy, controlling for extent in the three lateral gyri. Comparing preoperative to 6-month postoperative performance on a battery of intelligence, language and verbal memory tests revealed the following: a differential effect of the procedure was found for digit span, a short-term memory and attention task, the SR group showing a gain and the TR group a loss postoperatively. This could be explained by a rather large improvement of the SR group with below average resection sizes in the superior temporal gyrus (STG) (2.8 cm), which small resections are nearly absent in TR resections. Effect of larger extent on the STG in the SR group was related to a decrease in verbal intelligence and a tendency in auditory comprehension which poses a risk in 'large' standard resections. Differences in extent of resection on the other gyri did not cause differences in effects on language functioning or verbal memory.In standard anterior temporal lobe resections only (without intraoperative language mapping) up to a limit of 4.5 cm, large resections on the STG pose a risk for declining on verbal IQ and auditory comprehension. In general, tailored resections (with language mapping) result in decline on a task measuring short-term memory and attention.

Dementia research suggests executive dysfunction is best understood within the context of disease-specific neuropathology. Leukoaraiosis (LA) results in executive dysfunction yet little is known about its impact on specific aspects of working memory (WM). This study aimed to investigate the relationship between MRI LA severity and WM in dementia. A visual rating scale was used to assign patients with dementia into groups with minimal-mild LA (Low LA; n = 34) and moderate-severe LA (High LA; n = 32). A modified Digit Span Backward Task consisting of 3-, 4-, and 5-span trials measured specific components of WM. Short-term storage and rehearsal in WM were assessed by the total number of digits reported regardless of recall order (ANY-ORDER; e.g., 47981 recalled ‘18943’, score = 4). Mental manipulation in the form of disengagement and temporal re-ordering was assessed by the total number of digits recalled in correct position (SERIAL-ORDER; e.g., 47981 recalled ‘18943’, score = 3). There was no difference between LA groups on ANY-ORDER comparisons. The High LA group obtained lower SERIAL-ORDER scores than the Low LA group. Stepwise regression analyses were conducted that first entered MMSE scores then composite z-scores reflecting executive functioning, language and memory. ANY-ORDER performance variance was explained solely by dementia severity. SERIAL-ORDER performance variance was further explained by executive dysfunction. Results suggest that high degrees of LA do not interfere with immediate (digit) recall but do interfere with disengagement and temporal re-ordering. LA may disconnect the frontal lobes from subcortical and cortical structures that form the neuronal networks critical for these WM functions.

Dense-array (128-channel) electroencephalography (EEG) was used to record event-related potentials (ERPs) from 33 participants between 7 and 16 years of age while they performed a Go/Nogo task. The frontal (Nogo) N2 component of the ERP was taken as an index of cognitive control, and examined in relation to both age and independent assessments of executive function (EF), including the Iowa Gambling Task (IGT), the Stroop task, a delay discounting task, and backward digit span. Better performance on the IGT and the Stroop task was associated with smaller N2 amplitudes, over and above effects of age. N2 latencies decreased with age but were not predicted by EF. Source modeling of the N2 revealed neural generators in areas suggestive of cingulate cortex and orbitofrontal cortex, and the locations of these generators varied systematically with EF (IGT and Stroop task): the cingulate generator was more anterior for good EF participants at all ages; the orbitofrontal generator was relatively left lateralized for younger and for poorer EF participants. Taken together, these findings suggest that age-related decreases in N2 amplitude, but not N2 latency, reflect the development of cognitive control and cannot be attributed solely to incidental changes that may affect assessments of the N2 (e.g., increases in skull thickness). Functionally relevant decreases in N2 amplitude may reflect changes in the regions of cortex giving rise to the N2.

Two groups of non-demented individuals, who differed on genetic risk for Alzheimer's disease (AD) based on their apolipoprotein E (APOE) genotype, were tested on a category fluency task. Twenty varepsilon4 carriers and twenty varepsilon4 non-carriers were tape recorded while saying animal names for ten minutes. Five measures were examined: total names generated; total clusters; mean cluster size; mean within-cluster retrieval time; and mean between-cluster retrieval time. Groups were matched on age and education and scored as normal on a battery of psychometric tests. The varepsilon4 carriers generated significantly fewer names and clusters, and took significantly longer to access clusters, when compared to the varepsilon4 non-carriers. No group differences were found for cluster size or within-cluster retrieval times. We previously reported [Rosen, V. M., Bergeson, J. L., Putnam, K., Harwell, A., Sunderland, T. (2002). Working memory and apolipoprotein E: What's the connection? Neuropsychologia 40, 2226-2233] that the varepsilon4 carriers in the present study scored significantly lower than the varepsilon4 non-carriers on a measure of working memory/attentional capacity [Operation Span Task, see Turner, M. L., Engle, R. W. (1989). Is working memory capacity task dependent? Journal of Memory and Language 28, 127-154]. In the present study, a significant negative relationship found between span performance and between-cluster retrieval times suggested that reduced attentional capacity may have negatively impacted semantic access for the varepsilon4 carriers. Finally, we found significant relationships between a Trail Making Test [Reitan, R. M. (1992). Trail Making Test, manual for administration and scoring. Tucson, AZ: Reitan Neuropsychology Laboratory] "switch" measure (Form B-Form A) and three of the five fluency measures. The findings suggested that the varepsilon4 carrier's reduced attentional capacity may have interfered with their covertly shifting attention among subcategories in the fluency task, resulting in fewer names and clusters generated and longer times to access clusters.

This study explored possible reasons for the striking difference between digit span and word span in patients with semantic dementia. Immediate serial recall (ISR) of number and non-number words was examined in four patients. For every case, the recall of single-digit numbers was normal whereas the recall of non-number words was impaired relative to controls. This difference extended to multi-digit numbers, and remained even when frequency, imageability, word length, set size and size of semantic category were matched for the numbers and words. The advantage for number words also applied to the patients' reading performance. Previous studies have suggested that semantic memory plays a critical role in verbal short-term memory (STM) and reading: patients with semantic dementia show superior recall and reading of words that are still relatively well known compared to previously known but now semantically degraded words. Additional assessments suggested that this semantic locus was the basis of the patients' category-specific advantage for numbers. Comprehension was considerably better for number than non-number words. Number knowledge may be relatively preserved in semantic dementia because the cortical atrophy underlying the condition typically spares the areas of the parietal lobes thought to be crucial in numerical cognition but involves the inferolateral temporal-lobes known to support general conceptual knowledge. © 2003 Elsevier Ltd. All rights reserved.

It is suggested that Alzheimer's disease (AD) patients are able to recall more items on the digit span task than on immediate free recall from a supraspan word list. Two experiments were undertaken to verify this assertion and to understand the basis of the putative span/supraspan discrepancy. The first experiment, involving 35 mildly or moderately demented AD patients, confirmed that digit span significantly exceeded immediate recall from a 10-item supraspan word list. Although digit span also exceeded supraspan recall in 38 elderly non-demented control subjects, the discrepancy was significantly greater within the AD group. In a second experiment, 19 AD cases and 20 controls were assessed with a word span task that used nouns matched by frequency and word length to nouns on the supraspan task. The magnitude of the span/supraspan discrepancy was reduced, indicating that part of the initial discrepancy was due to differences in stimulus items (digits versus common nouns). As before, AD subjects recalled more words on the span task than the supraspan task. However, in striking contrast, NC subjects recalled more words on the supraspan task, further indicating that AD patients are particularly impaired on supraspan recall. Using combined data from 106 subjects in both experiments, digit span performance correlated significantly with supraspan recall for NC but not AD subjects. Moreover, within the AD group the magnitude of the discrepancy was inversely related to a working memory measure derived from the backward digit span. The magnitude of the span/supraspan discrepancy correctly classified 88% of patients with mild dementia and 74% of controls. Results indicate that AD patients are specifically vulnerable to information overload inherent in the supraspan task, a view consistent with the perspective that AD is characterized by prominent disturbances in working memory.

Theoretical and empirical research on the cognitive functions of the prefrontal cortex have established that this region mediates what have been called 'executive' processes that can influence working and long-term memory. Despite the accumulation of such empirical evidence, the dependence of purely mnemonic portions of memory tasks on PFC remains unresolved. To address this issue, we performed an analysis of reports of performance on tests of working memory of patients with lesions of the dorsolateral prefrontal cortex, focusing on published reports in the literature of simple span and delayed-response tasks. We found that none of the eleven studies of forward verbal and spatial span in patients with prefrontal cortical lesions that we reviewed (reflecting the performance of 166 individual patients) demonstrated a statistically significant deficit relative to normal controls. In contrast, our review of the delayed-response literature indicated that there are conditions under which PFC lesions disrupt delayed-response performance. Based on the results of our review of the literature, we present testable hypotheses about the working memory functions of the PFC.

Evidence showing that non-verbal short-term memory has distinct visual and spatial/sequential components is reviewed. A new test, The Visual Patterns Test (VPT), which was designed to measure short-term visual memory largely shorn of its spatio-sequential component, is described. Correlational studies of the VPT and the Corsi Blocks Test with healthy subjects and brain-damaged patients indicate a separation between visual and sequential abilities. This separation of function is supported by double dissociations shown by patients. Moreover, in a selective interference experiment, the VPT and the Corsi tests were found to show a double dissociation pattern of interference from visual and spatio sequential subsidiary tasks, respectively. The present results are discussed in relation to other findings in the literature, and it is concluded that non-verbal short-term memory can indeed be viewed as comprising distinct visual and spatio-sequential components. The VPT will be a useful neuropsychological instrument for measuring the visual component.

Digit span (DS) and visual–spatial memory span (VMS) tasks have been considered indices of auditory and visual–spatial processing, respectively, often classified as ‘‘primary memory’’ or ‘‘attention’’. There has been limited evidence for their modality specificity, however. We present two children who showed visual–spatial processing deficiencies (including VMS) and non-dominant manual inefficiency with normal visual–spatial perception, auditory–verbal processing and dominant fine manual skills. These children support a distinction between auditory and visual–spatial memory span. These findings are discussed with regard to a hypothesis that the unique expression of VMS is time-limited, that visual–spatial processing becomes more verbalized as children learn to read and that these behavioral changes produce a lateral shift in cortical processing of visual–spatial information.

Although many individuals with traumatic brain injury (TBI) perform well on standard neuropsychological tests, they often exhibit marked functional difficulties. The functions which are impaired seem to be analogous to the role of the central executive system (CES) in Baddeley's [Working Memory, 1986, Oxford University Press, New York] widely accepted model of working memory. The purpose of this study was to investigate CES function in individuals with TBI with a dual-task paradigm. We studied 25 non-demented persons who were at various stages in their recovery from severe TBI and compared their performance on a dual-task paradigm to a group of age-matched controls. Our dual-task paradigm measured performance on a simple visual reaction time task both alone (baseline) and during concurrent tasks of articulation or digit span. Subjects were also assessed with other neuropsychological tests of executive function. TBI patients had slower reaction times on the primary task when performed alone (P < 0.05) and greater decrements in performance during dual-task conditions (P < 0.01). They also exhibited significantly greater deficits than control subjects on other measures of executive function. Although correlations between dual-task performance and other executive measures were quite low, principle components analysis suggested that a common factor does exist between these measures. These findings support the conclusion that TBI patients have a working memory impairment that is due to dysfunction of the CES and which may be related to executive function deficits as measured by standard neuropsychological testing.

Sixty-one acute and 17 chronic vascular left-hemisphere damaged patients were tested with five memory tasks that investigated verbal short-term (digit span) and long-term (paired-associate and story learning) memory, and spatial short- and long-term memory (Corsi's span and learning). Both brain-damaged groups were significantly impaired in all memory tasks (except for chronic patients in the story learning task) compared to normal controls. The presence of aphasia and locus of lesion (anterior, posterior and deep) had no effect on the memory impairment, with only one exception of paired-associate learning that was better performed by non-aphasic than aphasic patients. Eleven subjects were better at paired-associate learning than story recall, the reverse dissociation was never found. Finally, chronic patients performed significantly better than acute patients only in the Corsi's learning task.

The aim of this study was to investigate whether transcranial magnetic stimulation (TMS) can be used for a lateralization of verbal and non-verbal memory functions in candidates for epilepsy surgery by inducing focal, material-specific memory deficits. Twenty patients who underwent presurgical epilepsy evaluation with chronically implanted subdural strip electrodes were submitted to focal TMS over the temporal lobes and the vertex while sequences of items of the Digit Span and the Corsi Block test were presented on a computer screen. TMS was applied synchronously or 200 msec following presentation of each item. The effects of TMS on the memory span and the serial position curve were analysed in comparison to baseline levels. The following results were obtained: the quantitative effects on the verbal (Digit Span) and non-verbal (Corsi Block) memory span were not significant, but there were significant qualitative changes of serial position effects. In the group of six patients with left temporal epilepsy, TMS over the left temporal lobe induced a significant recency effect in the Digit Span test, while TMS over the vertex significantly increased the recency errors. The absolute number of errors remained unchanged. No such effects were observed in the group of nine patients with right temporal lobe epilepsy. These results suggest that in the presence of a left temporal lobe focus TMS can induce qualitative, material specific changes in verbal working memory (phonological loop) which become apparent in the serial position curve. The dissociation of TMS effects for temporal and vertex stimulation imply that TMS can selectively influence specific phonological loop components and that the phonological loop has a functionally and neuroanatomically multimodular structure.

This study compares the nature of the reading deficit that was observed in two dyslexic undergraduate students who were severely impaired at reading and spelling compared with normal undergraduates. They both achieved the same (below average) score on the National Adult Reading Test and on the Schonell spelling test. One of them, however, was good at reading and spelling nonwords, had good phonological awareness skills, was better at reading regular than irregular words, and made phonologically accurate reading and spelling errors (i.e. was a surface dyslexic). The other had poor phonological awareness, produced relatively few phonologically accurate spelling errors, and was poor at reading and spelling nonwords (i.e. was a phonological dyslexic). It is particularly noteworthy that such a clear dissociation between surface and phonological forms of developmental dyslexia occurred in two subjects who were closely matched in terms of their overall reading and spelling ability, and also in terms of their memory span and vocabulary. It is argued that this study strengthens the evidence for the existence of qualitatively different types of developmental dyslexia. The findings are also consistent with the view that phonological awareness skills are more closely related to the operation of the phonological rather than the visual reading route.

Korsakoff's syndrome often affects “executive” functions [Baddeley, A. Human Memory, Theory and Practice , 1990], which in anatomical terms are associated with the frontal lobes. However, in a previous study, Wiegersma, S. and de Jong, E. [ J. clin. exp. Neuropsychol. 13, 847-853, 1991] failed to observe a diminished performance on the random generation task, although this task is thought to be sensitive to “executive” deficits. In the present study, we sought to replicate and clarify these earlier findings of Wiegersma and de Jong with a group of Korsakoff patients in whom frontal lobe dysfunction was indicated by a reduced performance on fluency tasks. Patients and controls were presented with three tasks. Digit span was used as an index of short-term memory capacity; memory search and comparison processes were measured with the missing item scan; and the randomisation task was used to assess the ability to produce non-routine, random sequences. The results showed that the performance of Korsakoff patients declined on the randomisation task while short-term retention and scanning were intact. Analysis of the responses indicated that the Korsakoff patients are able to suppress the dominant response, but have problems in generating and carrying out alternative strategies in novel problem situations.

Two distinctly different maturational processes - cortical thinning and white matter maturation - take place in the brain as we mature from late childhood to adulthood. To what extent does each contribute to the development of complex cognitive functions like working memory? The independent and joint contributions of cortical thickness of regions of the left fronto-parietal network and the diffusion characteristics of the connecting pathway of the left superior longitudinal fasciculus (SLF) in accounting for verbal working memory performance were investigated, using a predefined regions of interest-approach. 108 healthy participants aged 8-19 years underwent MRI, including anatomical and diffusion tensor imaging (DTI), as well as cognitive testing using a digit span task. Radial diffusivity of the SLF, as well as cortical thickness of supramarginal gyrus and rostral middle frontal cortex, were negatively related to digit span forwards performance, independently of age. Radial diffusivity of the SLF was also negatively related to digit span backwards. A multi-modal analysis showed that cortical thickness and SLF microstructure were complementary in explaining working memory span. Furthermore, SLF microstructure and cortical thickness had different impact on working memory performance during the developmental period, suggesting a complex developmental interplay. The results indicate that cortical and white matter maturation each play unique roles in the development of working memory.

A contentious issue in memory research is whether verbal short-term memory (STM) depends on a neural system specifically dedicated to the temporary maintenance of information, or instead relies on the same brain areas subserving the comprehension and production of language. In this study, we examined a large sample of adults with acquired brain lesions to identify the critical neural substrates underlying verbal STM and the relationship between verbal STM and language processing abilities. We found that patients with damage to selective regions of left perisylvian cortex – specifically the inferior frontal and posterior temporal sectors – were impaired on auditory–verbal STM performance (digit span), as well as on tests requiring the production and/or comprehension of language. These results support the conclusion that verbal STM and language processing are mediated by the same areas of left perisylvian cortex.

Two experiments are described which investigate the short-term memory deficits found in Alzheimer-type dementia. In the first experiment memory span for words of differing spoken duration is related to speech rate. Memory span was lower in subjects suffering from Alzheimer-type dementia than for normal elderly controls but in both cases a linear function related recall to speech rate for items of differing spoken durations. The functions for Alzheimer subjects had an equivalent slope (interpreted as reflecting a contribution from a sub-vocal rehearsal process) but a lower intercept (interpreted as reflecting a contribution from a long-term memory component). The second experiment investigated the effects of repeating supra-span lists of items in a serial recall task. As predicted the control subjects showed substantial increases in recall across trials associated with elevations of the speech rate/recall functions while the Alzheimer subjects showed very little benefit from repetition of the lists. We conclude that the verbal short-term memory deficit found in Alzheimer-type dementia has two components: a deficit in the rate of rehearsal and an impairment in the long-term memory component of short-term recall.

The present study investigated executive neuropsychological functioning in individuals with the neuro-developmental disorder Williams syndrome (WS) using a set of validated standardized neuropsychological tasks. Relatively few studies have examined frontal lobe related executive functions within the cognitive phenotype associated with the disorder. The present study compared participants with WS to typically developing participants who were individually matched for (1) chronological age and (2) verbal mental age (N=19 each group) on tasks of attention-set shifting, planning and working memory from the Cambridge Neuropsychological Test Automated Battery (CANTAB). To address the specificity of executive function impairment, non-executive tasks of delayed short-term memory and short-term memory span were also administered. Individuals with WS (mean age 18 years) showed impaired executive functioning on tasks of attention set-shifting, working memory, and planning. Non-executive deficits were also observed in short-term delayed memory and memory span. Neuropsychological impairments were correlated with a range of behavioural problems assessed using parent-rated Questionnaires. Overall, these findings point to the role of a range of executive function impairments in WS but further suggest that cognitive impairments extend beyond executive dysfunction.

Although monkey lesion studies involving the prefrontal cortex commonly report working memory deficits, and neuroimaging studies consistently show prefrontal involvement in such tasks, patients with damage to this region commonly fail to show any working memory impairment. Such a discrepancy may be due to insensitive testing measures for patients, as well as small, yet critical differences between working memory tasks in imaging and patient studies. The current study utilised a more sensitive measure of spatial working memory spans, based either on structured or unstructured spatial arrays. A PET study in normal subjects confirmed that both variants did indeed activate prefrontal cortex. The same tasks were given to frontal lobe patients and closely matched controls. Patients with large frontal lesions were significantly impaired on this task, with those patients with damage to the right dorsolateral prefrontal cortex appearing particularly impaired. This result demonstrates that prefrontal cortex is necessary for normal working memory, even in simple tasks, such as spatial span. It is suggested, however, that the patient deficit reflects strategic or goal-based dysfunction, rather than storage limitations.

Although dopamine has been closely associated with prefrontal function, and with working memory in monkeys, the effects of dopamine agonists on human cognitive performance are poorly understood. We report the effects of a single dose of pergolide on young healthy subjects performing a variety of cognitive tests, including tests of memory and of frontal/executive function. Across this battery of tasks, the only tasks reliably affected by pergolide were delayed response tasks. Across four variants, we observed that the effect of pergolide was more beneficial for subjects with greater working memory capacities. We discuss this in light of the variable results obtained from previous studies of dopamine agonists in human subjects.

The performance of developmentally dyslexic children and adults was studied upon a range of tasks that involved executive functioning. Both adult and child samples of dyslexics were found to under-perform on the group-embedded figures test. This test required the identification of constituent parts from within complex visual arrays, with good performance necessitating the inhibition of the processing of the surrounding context. A general deficit on visual-spatial tasks was eliminated as an explanation as dyslexics performed normally upon a range of other non-verbal assessments. The dyslexics consistently demonstrated a deficit in digit span tasks, a decrement that was increased with distractors, again suggesting difficulties in inhibiting the processing of the surrounding context. A deficit was also identified upon a verbal fluency task without a deficit in vocabulary level. Additionally, a specific deficit in the recollection of the temporal order of the presentation of items was in evidence, without a deficit in the recognition of the items themselves. The findings taken as a whole suggest that dyslexic individuals show deficiencies in executive functions relating to inhibition of distractors and to sequencing of events, a set of tasks associated with left prefrontal cortex functioning in the acquired neuropsychology literature.

Spatial memory is one of the most important cognitive functions in daily life, enabling us to locate objects in our environment or to learn a route or a path. In the present study, we elaborated on the hypothesis that human spatial memory consists of multiple sub-processes, relying on different brain structures. Therefore, 50 patients with an ischemic stroke and 40 healthy participants underwent tests measuring spatial span and maze learning. By means of a computer paradigm the following aspects of memory for object locations were assessed: (1) object location binding; (2) positional memory; (3) a combination of these two aspects. The results clearly showed a double dissociation: the group of patients with an infarct in the left hemisphere (LH) was impaired on object location binding, whereas the group with an infarct in the right hemisphere (RH) was impaired on positional memory. Lesions in the RH resulted also in impairments on maze learning. Moreover, patients with lesions in the posterior part of the parietal or the occipital lobe performed especially worse on spatial-memory tasks. These findings extend the theoretical framework of categorical versus coordinate spatial processing in the human brain and corroborate previous findings on selective aspects of memory for object locations.

Striatofrontal circuits have been implicated in spatial working memory in non-human and human primates. To determine at which steps of information processing (stimulus encoding, storage or response programming) they intervene, we compared 32 levodopa-treated patients with idiopathic Parkinsons disease (PD) and 32 matched control subjects in a visuo–spatial pattern span paradigm. Our testing procedure allowed us to evaluate the influence of: (1) the type of encoding (controlled vs free); (2) the nature of interference during a 10 s delay (spatial vs verbal); and (3) response elaboration (reproduction vs error detection). As expected, the performance of control subjects was significantly better in controlled than in free encoding, in verbal than in spatial interference and in detection than in reproduction, clearly demonstrating the sensitivity of the procedure to these factors. Compared to controls, PD patients were impaired in all conditions and the severity of the deficit was significantly correlated with that observed in tests of executive functions. The global pattern of performance, however, was identical to that of controls. These data confirm the involvement of striatofrontal circuits in spatial working memory in humans and suggest that the executive working memory component intervenes at all steps of working memory processing.

The neural processes that underlie the functional emergence of human cognitive functions, particularly those associated with the prefrontal cortex (PFC), are of growing interest to developmental psychologists and neuroscientists. Specifically, working memory functions have been correlated with PFC activity in nonhuman primates and adult humans but have not been extensively studied in children. We examined the developmental emergence of functions involved in working memory through the use of the Cambridge Neuropsychological Test Automated Battery (CANTAB), a computerized battery of nonverbal visually-presented neuropsychological tests designed to dissociate frontal from temporal lobe behavioral functions. Participants were normal children, aged 4-8 (n = 181) and a small group of young adults (n = 24) who completed measures of Spatial Memory Span, Spatial Working Memory, the Tower of London planning task, Visual Pattern and Spatial Recognition tasks, and a Set-Shifting task. Findings indicate a general age-related progression in ability levels on frontal lobe tasks, with 4-year-olds performing worse than 5- to 7-year-olds on all measures. Eight-year-olds are superior to younger children in their ability to solve complex problems but have not yet reached adult levels of performance on the most difficult items of the Tower of London and Spatial Working Memory tasks. We conclude that the development of working memory functions proceeds dimensionally, starting with refinement of basic perceptual and sensorimotor functions and culminating with the physiological maturation of widespread neural networks that integrate complex processing demands inherent to working memory tasks.

Young and old subjects participated in an experiment in which trials testing memory for temporal order (recency memory) and recognition memory were randomly intermixed with study trials in a continuous sequence. A dissociation was found between recency and recognition memory performance for pictorial stimuli. Relative to young adults, older adults performed at chance on recency memory trials whereas they were not impaired on recognition memory. Recency performance was correlated with measures derived from the Wisconsin Card Sorting test, whereas recognition performance was not. The results are discussed in terms of the role of the frontal lobes in temporal-order memory and of possible frontal lobe deterioration in normal aging.

This study tested the alternative hypotheses of Weinberg et al. (J. clin. Psychol. 28, 361, 1976) and Robertson (Neuropsychologia 28, 217-222, 1990) regarding the nature of dysfunctions underlying impaired backward digit span among patients with unilateral neglect. Results support the Weinberg et al. hypothesis that visual imagery plays a primary role in performance of Digits Backward. The findings also indicate a unilateral component to the Digits Backward task. Both neglecting and non-neglecting patients with high digit span discrepancy (DD) evidenced attentional bias to right space and a specific impairment in rotating objects in left space. Results were not consistent with Robertson's hypothesis that high DD arises from a general attentional deficit. In fact, patients with low DD evidence greatest impairment on tests of attention.

Weinberg et al. found a relationship between the presence of extinction and the discrepancy between backward and forward digit span among left hemiplegic patients. The present study replicates this finding in a group of 37 patients suffering from unilateral left visual neglect, demonstrating a strong relationship between degree of neglect and digit span discrepancy. A principal components analysis of a neuropsychological examination revealed three main independent components—Neglect, Verbal Memory and Non-verbal Memory respectively. Digit Span Discrepancy had one of the highest loadings on the neglect factor, and loaded significantly on no other factor. Multiple regression analysis showed that the relationship of Digit Span Discrepancy with Degree of Neglect exists independently of visuo-spatial ability, and this is also true for paced auditory serial addition (PASAT) scores for one of the two main indices of neglect. The implications of this for understanding neglect are discussed.

Four tasks relying on short-term retention, i.e. digit span, missing scan, randomization span, and pointing span were presented to patients with frontal-lobe lesions and normal controls. Digit span was considered a measure of passive short-term memory, the other three tasks additionally reflect comparison processes, and two of these, the randomization and pointing spans, also measure active ordering by the subject. The results confirmed Petrides and Milner's (Neuropsychologia20, 249–262, 1982) hypothesis that frontal-lobe patients are typically deficient in subject-ordered tasks. It is also suggested that they are deficient in a spontaneous generation, rather than comparison, component of subjective ordering.

Two experiments are described in which reading disabled subjects and their normal controls were tested for their ability to abstract sequential regularities from a noisy background. Subjects were presented with an adaptation of the repeated digits task of H EBB (1961) and its spatial analogue the Corsi Blocks ( Milner , B. Br. Med. Bull.27, 272–277, 1971). Normal subjects had a digit span significantly better than their block span and also significantly better than that of the disabled readers. This suggested that normal subjects have better defined “storage filters” for digits or a specific advantage in the construction of ‘transitory filters’ for verbal material. There were no differences between groups on block span. On the repeated digit sequences normal readers abstracted a relatively stable “storage filter” in the first five recurrent trials whereas the disabled readers showed no discrimination until the last five recurrent trials. On the repeated blocks task the disabled group performed as well as normal readers. Taken together this data gives strong evidence for a specific deficit in verbal serial organization in disabled readers but does not support a general deficit in serial organization.

The WISC digit span scaled scores of 297 children with learning disabilities fell below any of their overall I.Q. measures. More than 30 per cent of these Ss also had a greater than normal difference of 3 or more digits between their forward and backward spans. When 292 Ss for whom neurological data were available were categorized according to their signs (none, predominantly left, right, or bilateral), Ss with right-sided signs (presumed left hemisphere damage) were worse on digits forward, while Ss with left-sided signs (presumed right hemisphere damage) were worse on digits backward. Most Ss who could not repeat digits backward at all had bilateral impairment. Analysis of the data by age, suggests that the large gap between forward and backward digits, characteristic of the group with left-sided signs, tends to increase with age since their ability to repeat digits forward improves without concommitant improvement in their ability to repeat them backward. Conversely, the backward span of the group with right-sided signs tends to “catch up” and even equal their limited forward repetition. The data appear to support a left-hemisphere-dependent auditory verbal component of the digit span task reflected in digits forward and a right-hemisphere-dependent, visuo-spatial component reflected in digits backward. The distribution of verbal and performance WISC scores of these Ss, as well as their forward and backward digit spans, suggest that patterns of adult hemispheric asymmetry are similar in children with restricted early brain damage.

A probe paradigm was used to assess memory for the surface structure of sentences in a group of anterior (Broca's) and a group of posterior (Wernicke's) aphasics. Three types of sentences were used: active, passive and center-embedded sentences. Results showed that for both patient groups memory for function words was especially impaired relative to the patient's ability to recover content words. Further, both groups had marked difficulties in remembering center-embedded sentences. A second experiment rules out the possibility that this latter result was due to the extra syntactic complexity of the center-embedded sentences. Results from both experiments were interpreted as indicating that neither anterior nor posterior aphasics have normal surface structure memory representations and that the aphasic's memory span for sentence material may be severely limited.