Anterior Cortical Regions Research Articles

Hierarchical error representation in medial prefrontal cortex

The medial prefrontal cortex (mPFC) is reliably activated by both performance and prediction errors. Error signals have typically been treated as a scalar, and it is unknown to what extent multiple error signals may co-exist within mPFC. Previous studies have shown that lateral frontal cortex (LFC) is arranged in a hierarchy of abstraction, such that more abstract concepts and rules are represented in more anterior cortical regions. Given the close interaction between lateral and medial prefrontal cortex, we explored the hypothesis that mPFC would be organized along a similar rostro-caudal gradient of abstraction, such that more abstract prediction errors are represented further anterior and more concrete errors further posterior. We show that multiple prediction error signals can be found in mPFC, and furthermore, these are arranged in a rostro-caudal gradient of abstraction which parallels that found in LFC. We used a task that requires a three-level hierarchy of rules to be followed, in which the rules changed without warning at each level of the hierarchy. Task feedback indicated which level of the rule hierarchy changed and led to corresponding prediction error signals in mPFC. Moreover, each identified region of mPFC was preferentially functionally connected to correspondingly anterior regions of LFC. These results suggest the presence of a parallel structure between lateral and medial prefrontal cortex, with the medial regions monitoring and evaluating performance based on rules maintained in the corresponding lateral regions.

Comparison of Regional Brain Perfusion Levels in Chronically Smoking and Non-Smoking Adults.

Chronic cigarette smoking is associated with numerous abnormalities in brain neurobiology, but few studies specifically investigated the chronic effects of smoking (compared to the acute effects of smoking, nicotine administration, or nicotine withdrawal) on cerebral perfusion (i.e., blood flow). Predominately middle-aged male (47 ± 11 years of age) smokers (n = 34) and non-smokers (n = 27) were compared on regional cortical perfusion measured by continuous arterial spin labeling magnetic resonance studies at 4 Tesla. Smokers showed significantly lower perfusion than non-smokers in the bilateral medial and lateral orbitofrontal cortices, bilateral inferior parietal lobules, bilateral superior temporal gyri, left posterior cingulate, right isthmus of cingulate, and right supramarginal gyrus. Greater lifetime duration of smoking (adjusted for age) was related to lower perfusion in multiple brain regions. The results indicated smokers showed significant perfusion deficits in anterior cortical regions implicated in the development, progression, and maintenance of all addictive disorders. Smokers concurrently demonstrated reduced blood flow in posterior brain regions that show morphological and metabolic aberrations as well as elevated beta amyloid deposition demonstrated by those with early stage Alzheimer disease. The findings provide additional novel evidence of the adverse effects of cigarette smoking on the human brain.

Action processing and mirror neuron function in patients with amyotrophic lateral sclerosis: an fMRI study.

Amyotrophic lateral sclerosis (ALS) is a highly debilitating and rapidly fatal neurodegenerative disease. It has been suggested that social cognition may be affected, such as impairment in theory of mind (ToM) ability. Despite these findings, research in this area is scarce and the investigation of neural mechanisms behind such impairment is absent. Nineteen patients with ALS and eighteen healthy controls participated in this study. Because the mirror neuron system (MNS) is thought to be involved in theory of mind, we first implemented a straightforward action-execution and observation task to assess basic MNS function. Second, we examined the social-cognitive ability to understand actions of others, which is a component of ToM. We used fMRI to assess BOLD activity differences between groups during both experiments. Theory of mind was also measured behaviorally using the Reading the Mind in the Eyes test (RME). ALS patients displayed greater BOLD activity during the action-execution and observation task, especially throughout right anterior cortical regions. These areas included the right inferior operculum, premotor and primary motor regions, and left inferior parietal lobe. A conjunction analysis showed significantly more co-activated voxels during both the observation and action-execution conditions in the patient group throughout MNS regions. These results support a compensatory response in the MNS during action processing. In the action understanding experiment, healthy controls performed better behaviorally and subsequently recruited greater regions of activity throughout the prefrontal cortex and middle temporal gyrus. Lastly, action understanding performance was able to cluster patients with ALS into high and lower performing groups, which then differentiated RME performance. Collectively, these data suggest that social cognition, particularly theory of mind, may be affected in a subset of patients with ALS. This impairment may be related to functioning of the MNS and other regions related to action processing and understanding. Implications for future research are discussed.

Are Auditory Hallucinations Related to the Brain's Resting State Activity? A 'Neurophenomenal Resting State Hypothesis'.

While several hypotheses about the neural mechanisms underlying auditory verbal hallucinations (AVH) have been suggested, the exact role of the recently highlighted intrinsic resting state activity of the brain remains unclear. Based on recent findings, we therefore developed what we call the 'resting state hypotheses' of AVH. Our hypothesis suggest that AVH may be traced back to abnormally elevated resting state activity in auditory cortex itself, abnormal modulation of the auditory cortex by anterior cortical midline regions as part of the default-mode network, and neural confusion between auditory cortical resting state changes and stimulus-induced activity. We discuss evidence in favour of our 'resting state hypothesis' and show its correspondence with phenomenal, i.e., subjective-experiential features as explored in phenomenological accounts. Therefore I speak of a 'neurophenomenal resting state hypothesis' of auditory hallucinations in schizophrenia.

Poster #S39 ENDOGENOUS TESTOSTERONE LEVELS ARE ASSOCIATED WITH NEURAL ACTIVITY IN MEN WITH SCHIZOPHRENIA DURING A FACIAL EMOTION PROCESSING TASK

Alteration in self-perception is a salient feature in major depression. Hyperactivity of anterior cortical midline regions has been implicated in this phenomenon in depressed adults. Here, we extend this work to depressed adolescents during a developmental time when neuronal circuitry underlying the sense of self matures by using task-based functional magnetic resonance imaging (fMRI) and connectivity analyses. Twenty-three depressed adolescents and 18 healthy controls (HC) viewed positive and negative trait words in a scanner and judged whether each word described them (‘self’ condition) or was a good trait to have (‘general’ condition). Self-perception scores were based on participants’ endorsements of positive and negative traits during the fMRI task. Depressed adolescents exhibited more negative self-perceptions than HC. Both groups activated cortical midline regions in response to self-judgments compared to general-judgments. However, depressed adolescents recruited the posterior cingulate cortex/precuneus more for positive self-judgments. Additionally, local connectivity of the dorsal medial prefrontal cortex was reduced during self-reflection in depressed adolescents. Our findings highlight differences in self-referential processing network function between depressed and healthy adolescents and support the need for further investigation of brain mechanisms associated with the self, as they may be paramount to understanding the etiology and development of major depressive disorder.

Partial Correction of the CNS Lysosomal Storage Defect in a Mouse Model of Juvenile Neuronal Ceroid Lipofuscinosis by Neonatal CNS Administration of an Adeno-Associated Virus Serotype rh.10 Vector Expressing the Human CLN3 Gene

Juvenile neuronal ceroid lipofuscinosis (JNCL or CLN3 disease) is an autosomal recessive lysosomal storage disease resulting from mutations in the CLN3 gene that encodes a lysosomal membrane protein. The disease primarily affects the brain with widespread intralysosomal accumulation of autofluorescent material and fibrillary gliosis, as well as the loss of specific neuronal populations. As an experimental treatment for the CNS manifestations of JNCL, we have developed a serotype rh.10 adeno-associated virus vector expressing the human CLN3 cDNA (AAVrh.10hCLN3). We hypothesized that administration of AAVrh.10hCLN3 to the Cln3(Δex7/8) knock-in mouse model of JNCL would reverse the lysosomal storage defect, as well as have a therapeutic effect on gliosis and neuron loss. Newborn Cln3(Δex7/8) mice were administered 3 × 10(10) genome copies of AAVrh.10hCLN3 to the brain, with control groups including untreated Cln3(Δex7/8) mice and wild-type littermate mice. After 18 months, CLN3 transgene expression was detected in various locations throughout the brain, particularly in the hippocampus and deep anterior cortical regions. Changes in the CNS neuronal lysosomal accumulation of storage material were assessed by immunodetection of subunit C of ATP synthase, luxol fast blue staining, and periodic acid-Schiff staining. For all parameters, Cln3(Δex7/8) mice exhibited abnormal lysosomal accumulation, but AAVrh.10hCLN3 administration resulted in significant reductions in storage material burden. There was also a significant decrease in gliosis in AAVrh.10hCLN3-treated Cln3(Δex7/8) mice, and a trend toward improved neuron counts, compared with their untreated counterparts. These data demonstrate that AAVrh.10 delivery of a wild-type cDNA to the CNS is not harmful and instead provides a partial correction of the neurological lysosomal storage defect of a disease caused by a lysosomal membrane protein, indicating that this may be an effective therapeutic strategy for JNCL and other diseases in this category.

Magnetoencephalography Coherence Source Imaging in Dyslexia: Activation of Working Memory Pathways

This study investigates the functional connectivity of neuronal networks critical for working memory in individuals with dyslexia by means of magnetoenchephalographic (MEG) coherence imaging. Individuals with dyslexia showed an early onset of activation in anterior cortical regions (precentral gyrus and the superior frontal gyrus), which differed from controls where activation initiated in posterior cortical regions (supramarginal gyrus and superior temporal gyrus). Further, individuals with dyslexia showed lower brain activity in the right superior temporal gyrus and right middle temporal gyrus than controls during a spatial working memory (SWM) task. In contrast, during a verbal working memory (VWM) task, individuals with dyslexia showed lower activity in the right insular cortex and right superior temporal gyrus and higher, likely compensatory, activity in the right fusiform gyrus, left parahippocampal gyrus, and left precentral gyrus. When performing a SWM task, individuals with dyslexia showed significantly lower coherent activity and synchronization in 1) right frontal connectivity, 2) right fronto-temporal connectivity, 3) left and right frontal connectivity, 4) left temporal and right frontal connectivity, and 5) left occipital and right frontal connectivity. MEG coherence source imaging (CSI) by frequency bands showed lower mean coherence values in individuals with dyslexia compared to controls for each frequency range during the SWM task. In contrast, during the VWM task, individuals with dyslexia showed higher coherent low frequency (3 - 15 Hz) and lower coherent high frequency (30 - 45 Hz) synchronization than control subjects. Logistic regression of coherent activity by group membership was significant, with an overall predictive success of 84.4% (88.9% for controls and 77.8% for dyslexia). Coherence between the right lateral orbitofrontal and middle orbitofrontal gyri pair substantially contributed to group membership. The results suggest a pattern of aberrant connectivity as evidenced by the early onset and reliance on prefrontal cortical areas, the differential activation of fronto-temporal brain systems, and an altered pattern of functional connectivity in the frontotemporal pathways mediating these behaviors.

Damage to the anterior arcuate fasciculus predicts non-fluent speech production in aphasia

Non-fluent aphasia implies a relatively straightforward neurological condition characterized by limited speech output. However, it is an umbrella term for different underlying impairments affecting speech production. Several studies have sought the critical lesion location that gives rise to non-fluent aphasia. The results have been mixed but typically implicate anterior cortical regions such as Broca's area, the left anterior insula, and deep white matter regions. To provide a clearer picture of cortical damage in non-fluent aphasia, the current study examined brain damage that negatively influences speech fluency in patients with aphasia. It controlled for some basic speech and language comprehension factors in order to better isolate the contribution of different mechanisms to fluency, or its lack. Cortical damage was related to overall speech fluency, as estimated by clinical judgements using the Western Aphasia Battery speech fluency scale, diadochokinetic rate, rudimentary auditory language comprehension, and executive functioning (scores on a matrix reasoning test) in 64 patients with chronic left hemisphere stroke. A region of interest analysis that included brain regions typically implicated in speech and language processing revealed that non-fluency in aphasia is primarily predicted by damage to the anterior segment of the left arcuate fasciculus. An improved prediction model also included the left uncinate fasciculus, a white matter tract connecting the middle and anterior temporal lobe with frontal lobe regions, including the pars triangularis. Models that controlled for diadochokinetic rate, picture-word recognition, or executive functioning also revealed a strong relationship between anterior segment involvement and speech fluency. Whole brain analyses corroborated the findings from the region of interest analyses. An additional exploratory analysis revealed that involvement of the uncinate fasciculus adjudicated between Broca's and global aphasia, the two most common kinds of non-fluent aphasia. In summary, the current results suggest that the anterior segment of the left arcuate fasciculus, a white matter tract that lies deep to posterior portions of Broca's area and the sensory-motor cortex, is a robust predictor of impaired speech fluency in aphasic patients, even when motor speech, lexical processing, and executive functioning are included as co-factors. Simply put, damage to those regions results in non-fluent aphasic speech; when they are undamaged, fluent aphasias result.

Restoring Cortical Connectivity Directionality and Synchronization is Essential to Treating Disorder of Consciousness

The design of neurorehabilitation therapy to treat subjects with altered consciousness provides opportunities and challenges to professionals involved with the care for these severely ill patients. While there is an increased interest in determining methods to restore consciousness in these patients, the process is complex and challenging, due in part to the diverse aetiology of these states of consciousness, and also to the intricate cerebral connectivity involved in their treatment. The present case study examines a patient who showed signs of emergence from the vegetative state after neurorehabilitation using The Combined Method Therapy (CMT). In this case, neurorehabilitation therapy was applied simultaneously with pharmacological treatment, stimulation, and neuroimaging techniques to help adjust drug dosage. The results of this study suggest that this combined approach to treatment promoted connectivity among posterior and anterior cortical regions aiding emergence from the vegetative state.

Enhanced frontocentral EEG connectivity in photosensitive generalized epilepsies: A partial directed coherence study

Photosensitive epilepsy (PSE) is the most common form of reflex epilepsy presenting with electroencephalography (EEG) paroxysms elicited by intermittent photic stimulation (IPS). To investigate whether the neuronal network undergoes dynamic changes before and during the transition to an EEG epileptic discharge, we estimated EEG connectivity patterns in photosensitive (PS) patients with idiopathic generalized epilepsy. EEG signals were evaluated under resting conditions and during 14 Hz IPS, a frequency that consistently induces photoparoxysmal responses (PPRs) in PS patients. Partial directed coherence (PDC), a linear measure of effective connectivity based on multivariate autoregressive models, was used in 10 PS patients and 10 controls. Anterior versus posterior (F3, F4, C3, C4, and P3, P4, O1, O2) and interhemispheric connectivity patterns (F4, C4, P4, O2, and F3, C3, P3, O1) were estimated with focus on beta and gamma band activity. PDC analysis revealed an enhanced connectivity pattern in terms of both the number and strength of outflow connections in the PS patient group. Under resting condition, the greater connectivity in the PS patients occurred in the beta band, whereas it mainly involved the gamma band during IPS (i.e., the frequencies ranging from 40-60 Hz that include the higher harmonics of the stimulus frequency). Both at rest and during IPS, the differences between the PS patients and controls were due primarily to clearly increased connectivity involving the anterior cortical regions. Our findings indicate that PS patients are characterised by abnormal EEG hyperconnectivity, primarily involving the anterior cortical regions under resting conditions and during IPS. This suggests that, even if the occipital cortical regions are the recipient zone of the stimulus and probably hyperexcitable, the anterior cortical areas are prominently involved in generating the hypersynchronization underlying the spike-and wave discharges elicited by IPS.

Cardiorespiratory Fitness and Attentional Control in the Aging Brain

A growing body of literature provides evidence for the prophylactic influence of cardiorespiratory fitness on cognitive decline in older adults. This study examined the association between cardiorespiratory fitness and recruitment of the neural circuits involved in an attentional control task in a group of healthy older adults. Employing a version of the Stroop task, we examined whether higher levels of cardiorespiratory fitness were associated with an increase in activation in cortical regions responsible for imposing attentional control along with an up-regulation of activity in sensory brain regions that process task-relevant representations. Higher fitness levels were associated with better behavioral performance and an increase in the recruitment of prefrontal and parietal cortices in the most challenging condition, thus providing evidence that cardiorespiratory fitness is associated with an increase in the recruitment of the anterior processing regions. There was a top-down modulation of extrastriate visual areas that process both task-relevant and task-irrelevant attributes relative to the baseline. However, fitness was not associated with differential activation in the posterior processing regions, suggesting that fitness enhances attentional function by primarily influencing the neural circuitry of anterior cortical regions. This study provides novel evidence of a differential association of fitness with anterior and posterior brain regions, shedding further light onto the neural changes accompanying cardiorespiratory fitness.

The Neural Basis of Perceptual Category Learning in Human Infants

We measured looking times and ERPs to examine the cognitive and brain bases of perceptual category learning in 6-month-old infants. In Experiment 1, we showed that categorization and exemplar discrimination rely on different cortical processes. Specifically, the repetition of individual exemplars resulted in differential cortical processing at posterior channels at an early stage during object processing (100-300 msec), whereas discriminating among members of different categories was reflected in ERP differences over anterior cortical regions occurring later in time (300-500 msec) than the repetition effects. In Experiment 2, replicating the findings of Study 1, we found that infants engage the same cortical processes to categorize visual objects into basic-level categories, regardless of whether a basic (bird vs. fish) or global level is crossed (birds vs. cars). This pattern of findings is consistent with perceptual accounts of infant categorization [Quinn, P. C., & Eimas, P. D. Perceptual organization and categorization in young infants. In C. Rovee-Collier & L. P. Lipsitt (Eds.), Advances in infancy research ( pp. 1-36). Norwood, NJ: Ablex, 1996] and accords with recent adult neural-level models of perceptual categorization.

Frontal paralimbic network atrophy in very mild behavioral variant frontotemporal dementia.

Behavioral variant frontotemporal dementia (bvFTD) strikes hardest at the frontal lobes, but the sites of earliest injury remain unclear. To determine atrophy patterns in distinct clinical stages of bvFTD, testing the hypothesis that the mildest stage is restricted to frontal paralimbic cortex. A bvFTD cohort study. University hospital dementia clinic. Patients with bvFTD with Clinical Dementia Rating (CDR) scale scores of 0.5 (n = 15), 1 (n = 15), or 2 to 3 (n = 15) age and sex matched to each other and to 45 healthy controls. Magnetic resonance voxel-based morphometry estimated gray matter and white matter atrophy at each disease stage compared with controls. Patients with a CDR score of 0.5 had gray matter loss in frontal paralimbic cortices, but atrophy also involved a network of anterior cortical and subcortical regions. A CDR score of 1 showed more extensive frontal gray matter atrophy and white matter losses in corpus callosum and brainstem. A CDR score of 2 to 3 showed additional posterior insula, hippocampus, and parietal involvement, with white matter atrophy in presumed frontal projection fibers. Very mild bvFTD targets a specific subset of frontal and insular regions. More advanced disease affects white matter and posterior gray matter structures densely interconnected with the sites of earliest injury.

Enhanced metabolic capacity of the frontal cerebral cortex after Pavlovian conditioning

While Pavlovian conditioning alters stimulus-evoked metabolic activity in the cerebral cortex, less is known about the effects of Pavlovian conditioning on neuronal metabolic capacity. Pavlovian conditioning may increase prefrontal cortical metabolic capacity, as suggested by evidence of changes in cortical synaptic strengths, and evidence for a shift in memory initially processed in subcortical regions to more distributed prefrontal cortical circuits. Quantitative cytochrome oxidase histochemistry was used to measure cumulative changes in brain metabolic capacity associated with both cued and contextual Pavlovian conditioning in rats. The cued conditioned group received tone–foot-shock pairings to elicit a conditioned freezing response to the tone conditioned stimulus, while the contextually conditioned group received pseudorandom tone–foot-shock pairings in an excitatory context. Untrained control group was handled daily, but did not receive any tone presentations or foot shocks. The cued conditioned group had higher cytochrome oxidase activity in the infralimbic and anterior cingulate cortex, and lower cytochrome oxidase activity in dorsal hippocampus than the other two groups. A significant increase in cytochrome oxidase activity was found in anterior cortical areas (medial, dorsal and lateral frontal cortex; agranular insular cortex; lateral and medial orbital cortex and prelimbic cortex) in both conditioned groups, as compared with the untrained control group. In addition, no differences in cytochrome oxidase activity in the somatosensory regions and the amygdala were detected among all groups. The findings indicate that cued and contextual Pavlovian conditioning induces sustained increases in frontal cortical neuronal metabolic demand resulting in regional enhancement in the metabolic capacity of anterior cortical regions. Enhanced metabolic capacity of these anterior cortical areas after Pavlovian conditioning suggests that the frontal cortex may play a role in the retention and regulation of learned associations.

Incentive motivation is associated with striatal dopamine asymmetry

Dopamine plays an important role in modulating incentive motivation, expressed behaviorally as approach behavior. EEG studies report association between approach behavior and asymmetric pattern of activation in anterior cortical regions (as measured by the inverse of EEG alpha power). Therefore, individual differences in incentive motivation may reflect asymmetries in dopaminergic systems. We examined this hypothesis by studying the relationship between self-reported degree of incentive motivation, and asymmetry of D2 receptor availability in healthy volunteers. Nineteen healthy participants were studied with positron emission tomography (PET) and [11C]raclopride to assess the availability of dopamine D2 receptors in left and right striatum. Incentive motivation was assessed by the Achievement scale of the Multidimensional Personality Questionnaire. The Achievement score was negatively correlated with the Asymmetry Index ([R − L]/[R + L]) of D2 receptor availability ( r = −.721, p = .001), suggesting that greater positive incentive motivation is associated with higher receptor availability in the left relative to the right hemisphere.

Characteristics of the human EEG during cognitive-mnemenic activity under hypoxic conditions

The amplitude-frequency and spatiotemporal characteristics of the EEGs of subjects performing various cognitive-mnemenic activities under the conditions of graduated hypoxia were studied. The quickness and correctness of test performance were significantly decreased beginning from the sixth minute of hypoxia as compared to normoxic conditions. The amplitude and mean period of the dominant EEG activity in this func- tional state were higher than in the same tests performed under normoxic conditions and lower than in the case of hypoxia not accompanied by the performance of tests. The spatiotemporal characteristics of the EEG under hypoxic conditions displayed both the characteristics typical of hypoxia (a decrease in EEG cross-correlation within anterior cortical regions) and those typical of cognitive-mnemenic activity (an increase in the correlation between the EEGs of distant zones of anterior and posterior cortical regions). It is assumed that the "interme- diate" EEG pattern observed in subjects performing cognitive-mnemenic tests under hypoxic conditions reflects opposite effects of hypoxia and intellectual effort on the functional activity of brain neurons.

The Relationship Between Frontal Gray Matter Volume and Cognition Varies Across the Healthy Adult Lifespan

Age-associated decline in gray matter brain volume and cognitive function in healthy adults has been reported in the literature. The goal of the current study is to examine the relationship between age-related changes in regional gray matter volumes and cognitive function in a large, cross-sectional sample of healthy adults across the lifespan. Magnetic resonance imaging and cognitive assessment were conducted on 148 adults aged 21-76 years. Multiple regression analyses examining the effect of age were performed on magnetic resonance image-derived gray matter brain volumes and standardized cognitive summary scores of attention and executive function. Regression was also performed to test the effect of age, gray matter volumes, and their interaction on the prediction of cognitive performance. Age significantly predicted performance on tests of attention (F [1, 146]=50.97, p <0.01, R2=0.26) and executive function (F [1, 146]=126.19, p <0.01, R2=0.46) and gray matter volumes for frontal subregions (lateral, medial, orbital), hippocampus, amygdala, and putamen (F [2, 145]=45.34-23.96, p <0.01-0.02). Lateral frontal (beta=-1.53, t=-2.16, df=131, p <0.03) and orbital frontal (beta=1.24, t=2.08, df=131, p <0.04) regions significantly predicted performance on tests of attention. Lateral frontal (beta=-1.69, t=-2.83, df=131, p <0.01) and the interaction between age and lateral frontal volume (beta=3.76, t=2.49, df=131, p <0.02) significantly predicted executive function. The findings confirm age-associated decline in cognitive function and gray matter volumes, particularly in anterior cortical brain regions. Furthermore, the association between lateral frontal gray matter volume and the ability to successfully plan, organize, and execute strategies varies as a function of age across the healthy adult lifespan.

Changes in the spectral power and coherence of the EEG alpha rhythm in humans performing grasp efforts by the right and left arm

We compared changes in the EEG indices in healthy dextral volunteers performing static force grasps by the arm. Three test modes were used: (i) performance of two successive grasps by the dominant (right) arm (test A), (ii) performance of two successive grasps by the subdominant (left) arm (test B), and (iii) performance of the grasps first by the right arm and then by the left arm (test C). Fourteen, six, and nine persons took part in tests A–C, respectively. In the course of grasps performed by the right and left arms, bilateral increases in synchronization within the alpha 1 and alpha 2 ranges were frequently observed in occipital regions in both the first and repeated grasps (P < 0.05). Consecutive grasps by the right arm were accompanied by clear desynchronization in a few anterior and central leads. Alpha 2 desynchronization was observed in both realizations of the left-arm grasps (test B) performed by some subjects, but intragroup modifications were not significant in this case. The coherence coefficients of the alpha 2 rhythm in most cases increased for symmetric leads from the right and left hemispheres in the course of grasps by both the right and left hands. The effect of intensification of interhemisphere links was manifested in the anterior and central cortical regions; this fact showed that interhemisphere interaction increases in the course of the static effort. Changes in the coherence coefficients for the alpha 2 range in the performance of the grasp efforts by the right arm and the left arm were most clear in the posterotemporal (P = 0.02), parietal (P = 0.05), and anterofrontal (P = 0.06) lead pairs. Thus, we demonstrated the dependence between the side of performance of the muscle effort in the mode close to isometric and lateralization of the EEG modifications.

The neurophysiology of attention-deficit/hyperactivity disorder

Recent reviews of the neurobiology of Attention-Deficit/Hyperactivity Disorder (AD/HD) have concluded that there is no single pathophysiological profile underlying this disorder. Certainly, dysfunctions in the frontal/subcortical pathways that control attention and motor behavior are implicated. However, no diagnostic criteria or behavioral/neuroimaging techniques allow a clear discrimination among subtypes within this disorder, especially when problems with learning are also considered. Two major Quantitative EEG (QEEG) subtypes have been found to characterize AD/HD. Here we review the major findings in the neurophysiology of AD/HD, focusing on QEEG, and briefly present our previous findings using a source localization technique called Variable Resolution Electromagnetic Tomography (VARETA). These two techniques represent a possible objective method to identify specific patterns corresponding to EEG-defined subtypes of AD/HD. We then propose a model representing the distribution of the neural generators in these two major AD/HD subtypes, localized within basal ganglia and right anterior cortical regions, and hippocampal, para-hippocampal and temporal cortical regions, respectively. A comprehensive review of neurochemical, genetic, neuroimaging, pharmacological and neuropsychological evidence in support of this model is then presented. These results indicate the value of the neurophysiological model of AD/HD and support the involvement of different neuroanatomical systems, particularly the dopaminergic pathways.

Emotional-cognitive integration, the self, and cortical midline structures

Lewis discusses the dynamic mechanisms of emotional-cognitive integration. I argue that he neglects the self and its neural correlate. The self can be characterized as an emotional-cognitive unity, which may be accounted for by the interplay between anterior and posterior medial cortical regions. I propose that these regions form an anatomical, physiological, and psychological unity, the cortical midline structures (CMSs).