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Visual event-related potential (ERP) studies show effects due to target detection in the P3 and in earlier negativities over posterior recording sites. The topography of these earlier components suggests contributions from both anterior and posterior neural generators, however these studies were performed with sparse recording arrays and may not have provided a full description of the scalp topography of the visual ERP. The current study employed a high-density recording array (64 channels) and spherical spline interpolated topographic voltage and current density maps to describe the scalp distribution of the major deflections in the visual ERP from a visual oddball paradigm: the P1, N1, N2/P2a (a temporally coincident posterior negativity and anterior positivity) and P3. A modified difference wave analysis was also performed to track the time-course of target detection effects in the ERP. Target detection effects were found in the N2/P2a and P3 components. The scalp distribution of the N2/P2a was consistent with separate frontal and posterior neural generators and this is discussed in reference to human hemodynamic and nonhuman primate studies of neural activity in the inferior temporal visual object recognition system and in frontal systems of selective attention and working memory in visual target detection tasks.

Looking for an object that may be present in a cluttered visual display requires an advanced specification of that object to be created and then matched against the incoming visual input. Here, fast event-related fMRI was used to identify the brain networks that are active when preparing to search for a visual target. By isolating the preparation phase of the task it has been possible to show that for an identical stimulus, different patterns of cortical activation occur depending on whether participants anticipate a 'feature' or a 'conjunction' search task. When anticipating a conjunction search task, there was more robust activation in ventral occipital areas, new activity in the transverse occipital sulci and right posterior intraparietal sulcus. In addition, preparing for either type of search activated ventral striatum and lateral cerebellum. These results suggest that when participants anticipate a demanding search task, they develop a different advanced representation of a visually identical target stimulus compared to when they anticipate a nondemanding search. © 2013 Elsevier B.V. All rights reserved.

The present study employed high-density ERPs to examine the effect of induced sad mood on the spatiotemporal correlates of conflict monitoring and resolution in a colour-word Stroop interference task. Neuroimaging evidence and dipole modelling implicates the involvement of the anterior cingulate cortex (ACC) and medial prefrontal cortex (mPFC) regions in conflict-laden interference control. On the basis that these structures have been found to mediate emotion-cognition interactions in negative mood states, it was predicted that Stroop-related cognitive control, which relies heavily on anterior neural sources, would be affected by effective sad mood provocation. Healthy participants (N=14) were induced into transient sadness via use of autobiographical sad scripts, a well-validated mood induction technique (Liotti et al., 2000a, 2002). In accord with previous research, interference effects were shown at both baseline and sad states while Stroop conflict was associated with early (N450) and late (Late Positive Component; LPC) electrophysiological modulations at both states. Sad mood induction attenuated the N450 effect in line with our expectation that it would be susceptible to modulation by mood, given its purported anterior limbic source. The LPC effect was displayed at the typical posterior lateral sites but, as predicted, was not affected by sad mood. However, frontocentral LPC activity-presumably generated from an additional anterior limbic source-was affected at sad state, hinting a role in conflict monitoring. Although the neurophysiological underpinnings of interference control are yet to be clarified, this study provided further insight into emotion-cognition interactions as indexed by Stroop conflict-laden processing.

Psychological studies with reaction time methodology show that there is meaningful variability in the performance of cognitive operations when responses are measured in milliseconds. Temporal precision is also required to reveal the rapid neurophysiological events in cortical networks. Sampling the brain's electrical activity at the scalp surface characterizes regional brain function with millisecond temporal resolution. The problem with electroencephalographic (EEG) data is localizing the areas of the cortex that generate the observed scalp fields. Although the eventual goal will be to specify the neural generators of the EEG, we propose that an important first step for functional studies is to examine accurate, time-dynamic maps of the brain's electrical fields at the head surface. Given an adequate spatial sampling of the surface potentials, accurate electrical studies require measures that are independent of the location of the reference sensor. The 2D Laplacian of the potential field may be used to define the local features of the scalp current flow. Because the electrical fields are dynamic, brain mapping with electrical data requires animations rather than static images. © 1994 Wiley-Liss, Inc.

The electrophysiological correlates of conflict processing and cognitive control have been well characterized for the visual modality in paradigms such as the Stroop task. Much less is known about corresponding processes in the auditory modality. Here, electroencephalographic recordings of brain activity were measured during an auditory Stroop task, using three different forms of behavioral response (overt verbal, covert verbal, and manual), that closely paralleled our previous visual Stroop study. As was expected, behavioral responses were slower and less accurate for incongruent than for congruent trials. Neurally, incongruent trials showed an enhanced fronto-central negative polarity wave (N(inc)), similar to the N450 in visual Stroop tasks, with similar variations as a function of behavioral response mode, but peaking ~150 ms earlier, followed by an enhanced positive posterior wave. In addition, sequential behavioral and neural effects were observed that supported the conflict-monitoring and cognitive adjustment hypothesis. Thus, while some aspects of the conflict detection processes, such as timing, may be modality dependent, the general mechanisms would appear to be supramodal.

We present here the most comprehensive analysis to date of neuroaesthetic processing by reporting the results of voxel-based meta-analyses of 93 neuroimaging studies of positive-valence aesthetic appraisal across four sensory modalities. The results demonstrate that the most concordant area of activation across all four modalities is the right anterior insula, an area typically associated with visceral perception, especially of negative valence (disgust, pain, etc.). We argue that aesthetic processing is, at its core, the appraisal of the valence of perceived objects. This appraisal is in no way limited to artworks but is instead applicable to all types of perceived objects. Therefore, one way to naturalize aesthetics is to argue that such a system evolved first for the appraisal of objects of survival advantage, such as food sources, and was later co-opted in humans for the experience of artworks for the satisfaction of social needs.

The spatiotemporal dynamics of the hedonic response to chocolate images was investigated in healthy participants high and low in trait-chocolate craving employing high-density ERPs. There were two sessions: (1) before and (2) after satiety for chocolate. Among cravers, chocolate stimuli evoked a positive amplitude ERP enhancement over the anterior frontal scalp (250–350 ms) that was not modified by satiety and that source localized to the left lateral orbitofrontal cortex. Chocolate stimuli also elicited a later LPP over the posterior scalp (360–560 ms) which was of similar amplitude for high and low chocolate cravers, independent of satiety. Unexpectedly, in non-cravers, chocolate stimuli elicited an earlier (100–250 ms) negative ERP modulation over the frontomedial scalp, which disappeared after eating chocolate to satiety. These results confirm the role of OFC in unrestrained appetitive responses to chocolate in cravers, and suggest top-down influences from cognitive control mechanisms when attempting to restrain the urge to eat chocolate in non-cravers.

Previous neuroimaging work has identified anterior cingulate cortex (ACC) abnormalities in recurrent major depressive disorder (MDD), implicating a persistent underlying predisposition to depression. Error-monitoring studies in MDD, as indexed by error-related negativity (ERN), have yielded conflicting results, probably because of task differences or confounds in patient samples. ERN patterns were examined in remitted (n=19) and acutely depressed (n=17) patients, classified as a function of illness stage, and their matched controls in a go/no-go task using high-density ERPs. Results showed an abnormally larger ERN (p.05) in remitted patients, especially in younger cases. Overall, ERN was found to decrease with age across all groups. The findings of increased ERN in remitted depression may implicate an overactive ACC associated with a hypervigilant error-monitoring system. The observed tendency of ERN reduction in a severe depressive state failed to reach statistical significance.

The automatic orienting of attention was studied in medicated non-psychotic schizophrenic patients and in matched controls using the Posner paradigm of covert orienting to peripheral cues. This paradigm allows determination of the "benefits" in performance when attention is moved in advance to target location ("valid" trials) and the "costs" in performance when attention has to be reoriented to target location after an incorrect directional cue ("invalid" trials). Compared to normals, schizophrenics showed reduced costs of invalid cueing and increased benefits of valid directional cueing. Schizophrenics did not show selective visual field asymmetries reported in similar studies. The decreased inhibition in the presence of incorrect directional cues may be related to a reduced tone of monoaminergic terminals possibly involved in the regulation of selective attention and arousal regulation.

Deficits characteristic of attention deficit/hyperactivity disorder (ADHD), including poor attention and inhibitory control, are at least partially alleviated by factors that increase engagement of attention, suggesting a hypodopaminergic reward deficit. Lapses of attention are associated with attenuated deactivation of the default mode network (DMN), a distributed brain system normally deactivated during tasks requiring attention to the external world. Task-related DMN deactivation has been shown to be attenuated in ADHD relative to controls. We hypothesised that motivational incentives to balance speed against restraint would increase task engagement during an inhibitory control task, enhancing DMN deactivation in ADHD. We also hypothesised that methylphenidate, an indirect dopamine agonist, would tend to normalise abnormal patterns of DMN deactivation.We obtained functional magnetic resonance images from 18 methylphenidate-responsive children with ADHD (DSM-IV combined subtype) and 18 pairwise-matched typically developing children aged 9-15 years while they performed a paced Go/No-go task. We manipulated motivational incentive to balance response speed against inhibitory control, and tested children with ADHD both on and off methylphenidate.When children with ADHD were off-methylphenidate and task incentive was low, event-related DMN deactivation was significantly attenuated compared to controls, but the two groups did not differ under high motivational incentives. The modulation of DMN deactivation by incentive in the children with ADHD, off-methylphenidate, was statistically significant, and significantly greater than in typically developing children. When children with ADHD were on-methylphenidate, motivational modulation of event-related DMN deactivation was abolished, and no attenuation relative to their typically developing peers was apparent in either motivational condition.During an inhibitory control task, children with ADHD exhibit a raised motivational threshold at which task-relevant stimuli become sufficiently salient to deactivate the DMN. Treatment with methylphenidate normalises this threshold, rendering their pattern of task-related DMN deactivation indistinguishable from that of typically developing children.

International audience; OBJECTIVE:Previous studies have shown smaller brain volume and less gray matter in children with attention-deficit/hyperactivity disorder (ADHD). Relatively few morphological studies have examined structures thought to subserve inhibitory control, one of the diagnostic features of ADHD. We examined one such region, the pars opercularis, predicting a thinner cortex of the inferior frontal gyrus (IFG) in children with ADHD.METHOD:Structural images were obtained from 49 children (24 control; 25 ADHD combined subtype) aged 9 though 15 years. Images were processed using a volumetric pipeline to provide a fully automated estimate of regional volumes of gray and white matter. A further analysis using FreeSurfer provided measures of cortical thickness for each lobe, and for 13 regions in the frontal lobe.RESULTS:Relative to controls, children with ADHD had smaller whole brain volume and lower gray matter, but not white matter, volumes in all lobes. An analysis of frontal regions showed a significant interaction of group by region. Planned contrasts showed bilateral thinner cortex in the pars opercularis in children with ADHD.CONCLUSIONS:Children with ADHD showed both diffuse and regional gray matter abnormalities. Consistent with its putative role in response inhibition, the cortex of the pars opercularis was thinner in children with ADHD who, as expected, had significantly poorer inhibitory performance on a Go/No-go task. These differences held for both hemispheres raising the possibility that a developmental abnormality of IFG might drive development of inhibition difficulties.

Imitation in humans has been attributed to increased activation of the mirror neuron system, but there is no neural model to explain reciprocal communication. In this study, we investigated whether reciprocal, communicative, imitative exchanges activate the same neural system as imitation of simple movements, and whether the neural network subserving communication is lateralized. Fifteen participants were tested using functional magnetic resonance imaging with an online interactive-imitative paradigm while they performed finger movements for three different purposes: (1) to imitate the experimenter, (2) to elicit an imitation from the experimenter, and (3) to simply perform the movement. Subtraction analysis (imitation > movement, initiation > movement) revealed the activation of a strongly lateralized network, where the infra-parietal lobule (IPL) activation was lateralized to the left, while the infero-frontal gyrus (IFG) activation was to the right. It is concluded that imitation in a communicative paradigm recruits a lateralized network, with left fronto- and right parietal activation, that overlaps with a network that subserves understanding of an Other's intentions in relation to the Self. This finding lends plausibility to the suggestion that the neural network for imitation evolved to support interpersonal communication.

Children born very preterm, even with broadly normal IQ, commonly show selective difficulties in visuospatial processing and executive functioning. Very little, however, is known what alterations in cortical processing underlie these deficits. We recorded MEG while eight children born very preterm (≤32 weeks gestational age) and eight full-term controls performed a visual short-term memory task at mean age 7.5 years (range 6.4 – 8.4). Previously, we demonstrated increased long-range alpha and beta band phase synchronization between MEG sensors during STM retention in a group of 17 full-term children age 6–10 years. Here we present preliminary evidence that long-range phase synchronization in very preterm children, relative to controls, is reduced in the alpha-band but increased in the theta-band. In addition, we investigated cortical activation during STM retention employing synthetic aperture magnetometry (SAM) beamformer to localize changes in gamma-band power. Preliminary results indicate sequential activation of occipital, parietal and frontal cortex in control children, as well as reduced activation in very preterm children relative to controls. These preliminary results suggest that children born very preterm exhibit altered inter-regional functional connectivity and cortical activation during cognitive processing.

Several lines of evidence show impaired right hemisphere function in depression. Lateralized simple reaction time tasks show impaired left visual field responses both in normals experiencing a depressed mood and in patients with mild unipolar depression. One interpretation for these findings is that depression impairs right hemisphere function by interfering with right hemisphere arousal and vigilance mechanisms. In order to test this hypothesis, subjects receiving either depression or relaxation mood suggestions performed an uncued reaction time task that has been shown to be sensitive to right posterior brain damage. Level of alertness was varied by contrasting uncued blocks with blocks in which targets were preceded by a warning tone. The results showed the predicted slowing of left visual field responses in the depressed mood, but only in women. The effect was significant only for the uncued blocks. The left visual field impairment was significantly larger during depression than in the relaxation state, but a smaller left visual field slowing was present in women in the relaxed state as well. These results may be consistent with the notion that depression interferes with right hemisphere function in part by influencing right hemisphere arousal mechanisms.

Somatotopy within the orofacial region of the human motor cortex has been a central concept in inter- preting the results of neuroimaging and transcranial magnetic stimulation studies of normal and disor- dered speech. Yet, somatotopy has been challenged by studies showing overlap among the effectors within the homunculus. In order to address this dichotomy, we performed four voxel-based meta-anal- yses of 54 functional neuroimaging studies of non-speech tasks involving respiration, lip movement, tongue movement, and swallowing, respectively. While the centers of mass of the clusters supported the classic homuncular view of the motor cortex, there was significant variability in the locations of the activation-coordinates among studies, resulting in an overlapping arrangement. This ''somatotopy with overlap" might reflect the intrinsic functional interconnectedness of the oral effectors for speech production.

Executive function and working memory deficits are not only present in ADHD, but also in reading disorder (RD). Here, high-density ERPs were recorded during the Stop Signal Task in 53 children and adolescents: An ADHD-combined type group, a group with RD, and a healthy control group. The ADHD-C group displayed unique abnormalities of the frontal N200. Both healthy controls and RD groups showed a success-related right frontal N200 modulation, which was absent in the ADHD group. Second, for Success Inhibition trials, the ADHD-C had smaller right frontal N200 waves relative to healthy controls, while the RD group did not. In contrast, NoGo-P3 abnormalities were present both in the ADHD-C and RD groups. Impaired early response inhibition mechanisms, indexed by the frontal N200, appear to be limited to ADHD-C. In contrast, deficits in later cognitive control and error monitoring mechanisms, indexed by the NoGo-P3, appear to be present in both conditions.

High-density brain electrical activity elicited by physical threat, positive and neutral words were recorded in 33 healthy individuals screened for high or low anxiety sensitivity (AS) during a modified emotional Stroop task. The paradigm allowed the separate assessment of block and mixed-trial effects. In the block analysis, a significant emotional RT slowing was observed along with the modulation of a frontocentral negativity (350-400ms) in the high AS group only. In contrast, the mixed-trial analysis revealed a positive enhancement of the ERP to threat words peaking earlier (200-300ms) over anterior frontal scalp in the absence of RT slowing. This component was preceded by a very early positive modulation (peaking 50ms) in the high AS group only. It is concluded that frontal ERPs to physical threat words can distinguish the contribution of emotional conflict and emotional salience, particularly in individuals with high trait-anxiety.

Behavioral and neuropsychological functioning in unmedicated children with attention-deficit/hyperactivity disorder (ADHD) who have a history of medication treatment (Rx) versus those who are treatment naive (TN) has, to our knowledge, not been previously studied. Ninety-four children in four groups (ADHD/Rx, ADHD/TN, learning disabilities [LD], and controls) were evaluated, while unmedicated, on measures of achievement, neuropsychological functioning, and behavior. The ADHD/Rx group performed significantly better than the TN group on writing, Stroop interference, and measures of attention, and performed as well as the control group on executive functioning, verbal working memory, and academics. Behaviorally, the ADHD groups showed more difficulty with mood and externalizing behaviors compared with the LD and control groups, with the ADHD/TN performing the most poorly. Findings suggest that the ADHD/Rx group shows better executive and academic functioning even when unmedicated.

Deficits in response inhibition may be at the core of the cognitive syndrome in ADHD. Here, inhibitory control mechanisms were studied in 36 ADHD-combined type and 30 healthy children by exploring the event-related brain activity during the Stop Signal task. The influence of age, gender, and previous treatment history was evaluated. The ADHD group showed reduced N200 wave amplitudes. For successful inhibitions, the N200 reduction was greatest over right inferior frontal scalp, and only the control group showed a success-related enhancement of such right frontal N200. Source analysis identified a source of the N200 group effect in right dorsolateral prefrontal cortex. Finally, a late positive wave to failed inhibitions was selectively reduced only in treatment-naive ADHD children, suggesting that chronic stimulants may normalize late conscious error recognition. Both effects were independent of gender and age.

To examine the electrophysiological effects of methylphenidate (MPH) on inhibitory control in children with attention deficit/hyperactivity disorder (ADHD).Twelve children with ADHD performed the Stop Signal Task (SST) while event related potentials (ERP) were obtained. Each child completed two testing sessions, once on placebo and again on an individualized dose of MPH, with the order of medication administration counterbalanced. The following ERP parameters were studied: the N200, often seen as a measure of the activation of the inhibitory process, and the NoGo-P3, which may represent the degree of performance monitoring and/or error detection.MPH significantly improved behavioral performance on the SST. During successful inhibitions, MPH also significantly increased the amplitude of the right frontal N200, while during unsuccessful inhibitions MPH increased the amplitude of the NoGo-P3.MPH may improve inhibitory control by enhancing brain mechanisms that trigger the inhibitory process and make stopping a motor act more probable (reflected by increased N200) and by increasing attentional resources to the task when unsuccessful inhibitions occur (as reflected by increased NoGo-P3). These results are consistent with functional imaging studies suggesting a role for the right frontal inferior cortex and the cingulate cortex in the pathophysiology of ADHD.

Previous work has suggested that a bias against disconfirmatory evidence (BADE) may be associated with the schizophrenia spectrum. The current investigation focused on whether a BADE (1) overlaps with traditional measures of memory and executive functions or selectively taps into a unique aspect of cognition and (2) is correlated with delusional ideation but not with other aspects of schizotypy. Sixty-eight undergraduate students were administered the Schizotypal Personality Questionnaire (SPQ), the BADE test, the Rey Auditory Verbal Learning Test (RAVLT), the Wisconsin Card Sorting Test (WCST), the Trail Making Tests A and B (TMT), and tests used to estimate IQ. Factor analysis of all cognition measures resulted in a 6-factor solution, 4 of which reflected the 4 domains of neuropsychological tests (WCST, RAVLT, TMT, and IQ), and 2 of which reflected different aspects of the BADE test: Initial Belief and Integration of Disconfirmatory Evidence. This solution suggests that BADE measures were independent from the other cognitive domains measured. Integration of Disconfirmatory Evidence was the only factor that correlated with delusion-content subscales of the SPQ, providing support for the contribution of a BADE to delusional ideation.

Objective: To determine if there are differences in the volume of the caudate and anterior cingulate cortex (ACC) between children with attention deficit hyperactivity disorder (ADHD) and controls, and if such differences are related to the subjects’ history of stimulant treatment. Methods: We performed a case-control study in an academic medical center. Twenty-one healthy controls, 16 children with ADHD, combined type with a history of stimulant treatment, and 14 children with ADHD, combined type treatment naive, underwent structural MRI. All children with ADHD were medication-free at the time of the MRI. Regional hemispheric volumes (in cm 3 ) of caudate and anterior cingulate cortex were determined. Results: There were significant differences bilaterally on caudate volume for both ADHD groups vs controls, with no difference between the ADHD groups on either side. In contrast, the right ACC was significantly smaller for the ADHD-treatment naive (ADHD/TN) group compared to the ADHD-treated (ADHD/Rx) and control group. The volume of left ACC approached significance contrast between ADHD/RX and ADHD/TN. There were no differences found between the ADHD/Rx and controls on the ACC volumes bilaterally. Conclusions: The results from this study indicate a relationship of previous treatment history with caudate and anterior cingulate volumetric changes in children with attention deficit hyperactivity disorder–combined type.

A bias against disconfirmatory evidence (BADE) has been observed in schizophrenia, and in the present study we evaluated whether this extends to a nonclinical sample scoring high on a schizotypy scale. Thirty-seven high and 32 low schizotypy healthy participants were sequentially presented with three sentences that increasingly disambiguated the true content of a delusion-neutral scenario and were asked to rate the plausibility of four interpretations for this scenario. Relative to low schizotypy participants, high schizotypy participants continued to endorse their initial beliefs, even in the face of evidence that disconfirmed these beliefs. This result provides support for the "schizophrenia spectrum" account of psychosis.

Brain electrical activity associated with inhibitory control was recorded in ten ADHD and ten healthy children using high density event related potentials (ERPs) during the Stop Signal Task (SST). SST is a two-choice reaction time (RT) paradigm, in which subjects are required, on 25% of the trials, to withdraw their response upon presentation of a "Stop Signal". In the healthy children, the ERP evoked by the Stop Signal differed for successful inhibitions (SI) compared to failed inhibitions (FI), with greater amplitude of a positive wave peaking around 320 msec over anterior medial frontal scalp (P3a). Such success-related P3a activity was significantly reduced in amplitude in the ADHD group. In addition, the error related negativity (ERN), a sharp negative wave that is present selectively on error trials in choice RT experiments, peaking 100 ms after motor onset, and distributed over anterior medial frontal scalp, was also markedly reduced in the ADHD group. The scalp distribution of the group differences in P3a and the ERN is consistent with a reduction of activity of sources in dorsal anterior cingulate cortex (dACC), suggesting a global deficit in cognitive control operations subserved by dACC in ADHD.

Little is known about the physiological mechanisms subserving the experience of air hunger and the affective control of breathing in humans. Acute hunger for air after inhalation of CO 2 was studied in nine healthy volunteers with positron emission tomography. Subjective breathlessness was manipulated while end-tidal CO 2 - was held constant. Subjects experienced a significantly greater sense of air hunger breathing through a face mask than through a mouthpiece. The statistical contrast between the two conditions delineated a distributed network of primarily limbic/paralimbic brain regions, including multiple foci in dorsal anterior and middle cingulate gyrus, insula/claustrum, amygdala/periamygdala, lingual and middle temporal gyrus, hypothalamus, pulvinar, and midbrain. This pattern of activations was confirmed by a correlational analysis with breathlessness ratings. The commonality of regions of mesencephalon, diencephalon and limbic/paralimbic areas involved in primal emotions engendered by the basic vegetative systems including hunger for air, thirst, hunger, pain, micturition, and sleep, is discussed with particular reference to the cingulate gyrus. A theory that the phylogenetic origin of consciousness came from primal emotions engendered by immediate threat to the existence of the organism is discussed along with an alternative hypothesis by Edelman that primary awareness emerged with processes of ongoing perceptual categorization giving rise to a scene [Edelman, G. M. (1992) Bright Air, Brilliant Fire (Penguin, London)].

A functional MRI study compared activation in the red nucleus to that in the lateral cerebellar dentate nucleus during passive and active tactile discrimination tasks. The study pursued recent neuroimaging results suggesting that the cerebellum may be more associated with sensory processing than with the control of movement for its own sake. Because the red nucleus interacts closely with the cerebellum, the possibility was examined that activity in red nucleus might also be driven by the requirement for tactile sensory processing with the fingers rather than by finger movement alone. The red and dentate nuclei were about 300% more active (a combination of activation areas and intensities) during passive (non‐motor) tactile stimulation when discrimination was required than when it was not. Thus, the red nucleus was activated by purely sensory stimuli even in the absence of the opportunity to coordinate finger movements or to use the sensory cues to guide movement. The red and dentate nuclei were about 70% more active during active tactile tasks when discrimination was required than when it was not (i.e., for simple finger movements alone). Thus, the red nucleus was most active when the fingers were being used for tactile sensory discrimination. In both the passive and active tactile tasks, the observed activation had a contralateralized pattern, with stronger activation in the left red nucleus and right dentate nucleus. Significant covariation was observed between activity in the red nucleus and the contralateral dentate during the discrimination tasks and no significant correlation between the red nucleus and the contralateral dentate activity was detected during the two non‐discrimination tasks. The observed interregional covariance and contralateralized activation patterns suggest strong functional connectivity during tactile discrimination tasks. Overall, the pattern of findings suggests that the activity in the red nucleus, as in the lateral cerebellum, is more driven by the requirements for sensory processing than by motor coordination per se. Hum. Brain Mapping 10:147–159, 2000. © 2000 Wiley‐Liss, Inc.

Background: A core deficit in inhibitory control may account for a wide range of dysfunctional behaviors in attention-deficit/hyperactivity disorder (ADHD). Methods: Event-related potentials were measured in 10 children with ADHD and 10 healthy children during a task specifically involving response inhibition (Stop signal task). Results: In response to all Stop signals, control participants produced a large negative wave at 200 msec (N200) over right inferior frontal cortex, which was markedly reduced in ADHD children. The N200 amplitude was significantly correlated across subjects with response–inhibition performance. In response to the Go stimuli, ADHD children showed a reduced slow positive wave (250–500 msec) in anticipation of failed inhibitions over right frontal scalp regions. Conclusions: ADHD children appear to have an abnormality in an early-latency, right inferior frontal processing component critical to the initiation of normal response-inhibition operations. They also appear to have a right frontal abnormality associated to the covert processing of Go stimuli preceding failed inhibitions. By providing timing and processing component specificity, these results extend the findings of recent functional MRI studies of inhibitory control reporting right frontal abnormalities in ADHD.

Subjective and physiologic effects of 33% inhaled Xe were measured with 15O-water positron emission tomography (PET) in 3 subjects at rest and during visual stimulation. The procedure was well tolerated. Robust functional activations of the visual cortex were obtained after xenon (Xe) inhalation as well as air breathing. However, Xe inhalation was followed by smaller size, but significant decreases of regional cerebral blood flow (rCBF) in visual cortex relative to the air-breathing baseline, both during visual stimulation and at rest. No such decreases were found in other sensory or motor regions.

University students in either an optimistic or pessimistic mood state read brief stories of daily life events as event-related brain potentials were collected during the final word of each story. For subjects in a pessimistic mood, a bias to expect negative outcomes was seen as an N400/P300 effect over posterior scalp regions. For subjects in an optimistic mood, a differentiation between good and bad outcomes was also observed, but it was specific to medial frontal areas. Analysis of single-trial P300 latencies suggested that semantically incongruent and mood-incongruent outcome words resulted in increased median latency of the late positive complex (LPC) and resulted in increased variability of LPC latency across trials.

Several lines of evidence suggest impaired right hemisphere function in depression. In order to further investigate this phenomenon, simple reaction times (RTs) to lateralized visual stimuli were studied in patients with mild anipolar depression, in patients with chronic anxiety, and in medical patients free of psychiatric symptoms. The results showed a marked slowing of RTs to left visual field (right hemisphere) stimuli in depressed patients. Anxious patients showed a trend toward an opposite asymmetry, with slower responses to right field (left hemisphere) stimuli. In the nonpsychiatric group no visual field differences were present. The results are discussed in light of two alternative interpretations: depression may engage the right hemisphere's mechanisms, interfering with its functioning at a premotor level, or it may influence the regulation of performance by arousal and vigilance mechanisms lateralized to the right hemisphere, possibly operating at an earlier sensory stage.

A 44-year-old woman showed, following an episode of encephalitis, an impoverished knowledge of the meaning and attributes of words and their referents, in spite of intact command of grammatical-syntactic rules and preserved perceptual abilities. There was also a complete loss of the stock of notions she had acquired over her life and constituting the cultural background of a person, in contrast with normal memory for autobiographic events. The case is interpreted as an istance of semantic amnesia. MRI showed damage confined to the antero-medial part of the left temporal lobe.

We report a case of a patient with a left occipital lesion who presented a peculiar behavioral dissociation. He was able to copy pictures but not to draw a simple object without a visual model; the relationship among the component parts was altered in drawings produced under the guidance of his mental representations. We have called this disturbance “visuoimaginal constructional apraxia.” The mechanisms underlying visuoimaginal constructional apraxia are investigated in an attempt to contribute to studies on the nature of mental imagery.

It has been shown that spatial compatibility is due to a comparison between the spatial codes that describe stimulus and response positions. Such codes are often defined in right-left terms. There are, however, two types of right-left codes that can be used for describing a position in space. One is formed with relation to the egocentric axes and can be termed “side”, whereas the other is formed with relation to an external reference location and can be termed “relative position”. Five experiments were conducted to determine the role of these different codes in producing spatial compatibility effects. In Experiments 1 and 2 the position of the stimulus provided the relevant cue for choosing the correct response (i.e., the situation was typical of spatial compability proper), whereas in Experiments 3, 4, and 5 the stimulus provided a locational cue that was not necessary for choosing the correct response (i.e., the situation was typical of the Simon effect). The experimental manipulations concerned the task demands and the time elapsing between availability of the stimulus code and availability of the response code. The results showed that upon stimulus presentation, both stimulus codes (that concerning side and that concerning relative position) were formed, but experimental manipulations determined the one that was effective in yielding compatibility effects. When the task required the use of one type of code, then spatial compatibility depended on that code alone. When the two coding processes were separated in time, then spatial compatibility depended only on the code that was formed simultaneously with the response code.

Different features of stimuli present in the field of view appear to be registered in different cortical maps. How, then, are the features that come from the same object bound together rather than mistakenly assembled with features coming from other simultaneously present objects? One theory supposes that an attentional mechanism intercepts input coming from particular retinal locations at a way station prior to parsing of the features from the same object. Any enhancement (or facilitation) at that stage will cause all the features from that object to be modified simultaneously in the downstream registers. The imposed temporal synchronicity serves as the essential binding cue. Five experiments provided no support for the theory. There is no tendency for synchronicity of features to cause binding unless the features come from the same location. Location, rather than temporal synchronicity, appears to be the essential cue for binding.

Simple reaction times (RTs) to lateralized unstructured visual stimuli measured in normal subjects while they were carrying out concomitant oculomotor tasks. Four tasks were used. In the first task, subjects had to find the correct path in a maze presented at the centre of a screen; in the second task, subjects had to follow a bright dot moved on a screen with variable direction, trajectory and velocity with their eyes; in the third task, the subjects had to follow a bright dot moved back and forth either horizontally or vertically along the same trajectory and at a constant velocity; in the fourth task, the subjects had to monitor the movement of a bright dot moved with variable direction, trajectory and velocity without moving the eyes. In all tasks, with the exception of the third, there was a selective lengthening of RTs mediated by the right hemisphere. It is concluded that the right hemisphere is dominant in programming eye movements.