A resource model of the neural basis of executive working memory

Differences in neural activation between preterm and full term born adolescents on a sentence comprehension task: implications for educational accommodations

Adolescent survivors of preterm birth experience persistent functional problems that negatively impact academic outcomes, even when standardized measures of cognition and language suggest normal ability. In this fMRI study, we compared the neural activation supporting auditory sentence comprehension in two groups of adolescents (ages 9-16 years); sentences varied in length and syntactic difficulty. Preterms (n=18, mean gestational age 28.8 weeks) and full terms (n=14) had scores on verbal IQ, receptive vocabulary, and receptive language tests that were within or above normal limits and similar between groups. In early and late phases of the trial, we found interactions by group and length; in the late phase, we also found a group by syntactic difficulty interaction. Post hoc tests revealed that preterms demonstrated significant activation in the left and right middle frontal gyri as syntactic difficulty increased. ANCOVA showed that the interactions could not be attributed to differences in age, receptive language skill, or reaction time. Results are consistent with the hypothesis that preterm birth modulates brain-behavior relations in sentence comprehension as task demands increase. We suggest preterms' differences in neural processing may indicate a need for educational accommodations, even when formal test scores indicate normal academic achievement.

Maternal history of reading difficulty is associated with reduced language-related gray matter in beginning readers

Family history and poor preliteracy skills (referred to here as familial and behavioral risk, respectively) are critical predictors of developmental dyslexia. This study systematically investigated the independent contribution of familial and behavioral risks on brain structures, which had not been explored in past studies. We also examined the differential effects of maternal versus paternal history on brain morphometry, and familial risk dimensionally versus categorically, which were also novel aspects of the study. We assessed 51 children (5 to 6 years of age) with varying degrees of familial and behavioral risks for developmental dyslexia and examined associations with brain morphometry. We found that greater maternal history of reading disability was associated with smaller bilateral prefrontal and parieto-temporal gray, but not white matter volumes. Regressing out behavioral risk, socioeconomic status, and maternal education and other confounds did not change the results. No such relationship was observed for paternal reading history and behavioral risk. Results of cortical surface area and thickness further showed that there was a significant negative relationship between cortical surface area (but not thickness) and greater severity of maternal history, in particular within the left inferior parietal lobule, suggesting prenatal influence of maternal history on children's brain morphometry. The results suggested greater maternal, possibly prenatal, influence on language-related brain structures. These results help to guide future neuroimaging research focusing on environmental and genetic influences and provide new information that may help predict which child will develop dyslexia in the future.

Functional specificity for high-level linguistic processing in the human brain

Neuroscientists have debated for centuries whether some regions of the human brain are selectively engaged in specific high-level mental functions or whether, instead, cognition is implemented in multifunctional brain regions. For the critical case of language, conflicting answers arise from the neuropsychological literature, which features striking dissociations between deficits in linguistic and nonlinguistic abilities, vs. the neuroimaging literature, which has argued for overlap between activations for linguistic and nonlinguistic processes, including arithmetic, domain general abilities like cognitive control, and music. Here, we use functional MRI to define classic language regions functionally in each subject individually and then examine the response of these regions to the nonlinguistic functions most commonly argued to engage these regions: arithmetic, working memory, cognitive control, and music. We find little or no response in language regions to these nonlinguistic functions. These data support a clear distinction between language and other cognitive processes, resolving the prior conflict between the neuropsychological and neuroimaging literatures.

Complex span tasks and hippocampal recruitment during working memory

The working memory (WM) system is vital to performing everyday functions that require attentive, non-automatic processing of information. However, its interaction with long term memory (LTM) is highly debated. Here, we used fMRI to examine whether a popular complex WM span task, thought to force the displacement of to-be-remembered items in the focus of attention to LTM, recruited medial temporal regions typically associated with LTM functioning to a greater extent and in a different manner than traditional neuroimaging WM tasks during WM encoding and maintenance. fMRI scans were acquired while participants performed the operation span (OSPAN) task and an arithmetic task. Results indicated that performance of both tasks resulted in significant activation in regions typically associated with WM function. More importantly, significant bilateral activation was observed in the hippocampus, suggesting it is recruited during WM encoding and maintenance. Right posterior hippocampus activation was greater during OSPAN than arithmetic. Persitimulus graphs indicate a possible specialization of function for bilateral posterior hippocampus and greater involvement of the left for WM performance. Recall time-course activity within this region hints at LTM involvement during complex span.

Covariates of craving in actively drinking alcoholics

The goal of this cross-sectional study was to assess the relationship of alcohol craving with biopsychosocial and addiction factors that are clinically pertinent to alcoholism treatment. Alcohol craving was assessed in 315 treatment-seeking, alcohol dependent subjects using the Penn Alcohol Craving Scale questionnaire. Standard validated questionnaires were used to evaluate a variety of biological, addiction, psychological, psychiatric, and social factors. Individual covariates of craving included age, race, problematic consequences of drinking, heavy drinking, motivation for change, mood disturbance, sleep problems, and social supports. In a multivariate analysis (R(2)= .34), alcohol craving was positively associated with mood disturbance, heavy drinking, readiness for change, and negatively associated with age. The results from this study suggest that alcohol craving is a complex phenomenon influenced by multiple factors.

Domain-general mechanisms of complex working memory span

A new fMRI complex working memory span paradigm was used to identify brain regions making domain-general contributions to working memory task performance. For both verbal and spatial versions of the task, complex working memory span performance increased the activity in lateral prefrontal, anterior cingulate, and parietal cortices during the Encoding, Maintenance, and Coordination phase of task performance. Meanwhile, overlapping activity in anterior prefrontal and medial temporal lobe regions was associated with both verbal and spatial recall from working memory. These findings help to adjudicate several contested issues regarding the executive mechanisms of working memory, the separability of short-term and working memory in the verbal and spatial domains, and the relative contribution of short-term and long-term memory mechanisms to working memory capacity. The study also provides a vital bridge between psychometric and neuroimaging approaches to working memory, and constrains our understanding of how working memory may contribute to the broader landscape of cognitive performance.

How to test for dual-task-specific effects in brain imaging studies--an evaluation of potential analysis methods

The study of the concurrent performance of two tasks allows deep insights into the human cognitive system and, accordingly, an increasing number of brain imaging studies are conducted to identify the neuroanatomical correlates of such dual-task performance. In this overview we present currently used approaches to identify dual-task-specific activations in fMRI and PET studies. A comparison is made in order to identify the approaches which have the potential to validly detect dual-task-specific activation patterns, i.e. activation which cannot be explained by the individual performance of the component tasks alone. We demonstrate that while all approaches suffer from at least some drawbacks, the best (although potentially over-conservative) approach is to compare the dual task with the sum of the single tasks, the second-best is an interaction contrast, and the third-best a conjunction analysis. Comparisons of the dual task with the mean of single-task activity or with only one single task should be avoided except for a few specific situations. We generalize our conclusions to related research areas, such as multisensory integration or divided attention.

Working memory in early Alzheimer's disease: a neuropsychological review

BACKGROUND

Reports of the extent of working memory (WM) impairment in early Alzheimer's disease (AD) have been inconsistent. Using the model of WM proposed by Baddeley, neuropsychological evidence for the impairment of WM in early AD is evaluated.

METHOD

Literature searches were performed using Medline, PsycINFO and Embase databases. Individual papers were then examined for additional references not revealed by computerised searches.

RESULTS

Phonological loop function is intact at the preclinical and early stages of AD, becoming more impaired as the disease progresses. In mild AD, there is impairment on tasks assessing visuospatial sketchpad (VSS) function; however, these tasks also require executive processing by the central executive system (CES). There is evidence that the CES is impaired in mild AD and may be affected in the earlier preclinical stage of the disease. Episodic buffer function may be impaired but further research is required.

CONCLUSIONS

Future research into central executive functioning at the earliest stages of the disease, combined with further longitudinal studies, needs to be carried out. Tasks to assess the proposed functions of the episodic buffer and specific tests of the VSS suitable for AD subjects need to be developed and validated. Learning more about these processes and how they are affected in AD is important in understanding and managing the cognitive deficits seen in the early stages of AD.

Share or compete? Load-dependent recruitment of prefrontal cortex during dual-task performance

Dual-task performance requires flexible attention allocation to two or more streams of information. Dorsolateral prefrontal cortex (DLPFC) is considered important for executive function, and recent modeling work proposes that attention control may arise from selective activation and inhibition of different processing units within this region. Here, we used a tone discrimination task and a visual letter memory task to examine whether this type of competition could be measurable using a neuroimaging technique, the event-related optical signal, with high spatial and temporal resolution. Left and right DLPFC structures were differentially affected by task priority and load, with the left middle frontal gyrus (MFG) being preferentially recruited by the visual memory task, whereas the two tasks competed for recruitment, in a spatially segregated manner, in right MFG. The data provide support for a competition view of dual-task processing.

Disentangling the prefrontal network for rule selection by means of a non-verbal variant of the Wisconsin Card Sorting Test

This study disentangles the prefrontal network underlying executive functions involved in the Wisconsin Card Sorting Test (WCST). During the WCST, subjects have to perform two key processes: first, they have to derive the correct sorting rule for each trial by trial-and-error, and, second, they have to detect when this sorting rule is changed by the investigator. Both cognitive processes constitute key components of the executive system, which is subserved by the prefrontal cortex. For the current fMRI experiment, we developed a non-verbal variant of the WCST. Subjects were instructed either to respond according to a given sorting rule or to detect the correct sorting rule, like in the original version of the WCST. Data were obtained from 14 healthy male volunteers and analysed using SPM and a random effects model. All conditions activated a fronto-parietal network, which was generally more active when subjects had to search for the correct sorting rule than when the rule was announced beforehand. Significant differences between these two conditions were seen in the dorsolateral prefrontal cortex (PFC) and the parietal lobe. In addition, the data provided new evidence for the assumption of differentiated roles of the left and right prefrontal cortex. Although the right PFC showed a general involvement in response selection and the execution of goal directed responses, based on given rules, the left PFC was only activated when inductive reasoning and feedback integration was required.

Aberrant functional connectivity of dorsolateral prefrontal and cingulate networks in patients with major depression during working memory processing

BACKGROUND

In patients with major depressive disorder (MDD), functional neuroimaging studies have reported an increased activation of the dorsolateral prefrontal cortex (DLPFC) during executive performance and working memory (WM) processing, and also an increased activation of the anterior cingulate cortex (ACC) during baseline conditions. However, the functional coupling of these cortical networks during WM processing is less clear.

METHOD

In this study, we used a verbal WM paradigm, event-related functional magnetic resonance imaging (fMRI) and multivariate statistical techniques to explore patterns of functional coupling of temporally dissociable dorsolateral prefrontal and cingulate networks. By means of independent component analyses (ICAs), two components of interest were identified that showed either a positive or a negative temporal correlation with the delay period of the cognitive activation task in both healthy controls and MDD patients.

RESULTS

In a prefronto-parietal network, a decreased functional connectivity pattern was identified in depressed patients comprising inferior parietal, superior prefrontal and frontopolar regions. Within this cortical network, MDD patients additionally revealed a pattern of increased functional connectivity in the left DLPFC and the cerebellum compared to healthy controls. In a second, temporally anti-correlated network, healthy controls exhibited higher connectivity in the ACC, the ventrolateral and the superior prefrontal cortex compared to MDD patients.

CONCLUSIONS

These results complement and expand previous functional neuroimaging findings by demonstrating a dysconnectivity of dissociable prefrontal and cingulate regions in MDD patients. A disturbance of these dynamic networks is characterized by a simultaneously increased connectivity of the DLPFC during task-induced activation and increased connectivity of the ACC during task-induced deactivation.

Simple dual tasking recruits prefrontal cortices in chronic severe traumatic brain injury patients, but not in controls

The ability to carry out two tasks simultaneously, dual tasking, is specifically impaired after traumatic brain injury (TBI). The aim of the present study was to investigate the neuronal correlates to this increased dual cost in chronic severe TBI patients (n = 10) compared to healthy controls (n = 11) using functional magnetic resonance imaging (fMRI) at 3 Tesla (T). The tasks were a visual search and a simple two-fingers button press motor task. Performance data demonstrated similar and significant dual task interference in both TBI patients and controls using a linear mixed model. However, principal component analysis showed that TBI patients and controls could be classified into different categories based on motor activity in the single compared to the dual task condition, thus reflecting the increased variability in the performance in the TBI group. Random effects between-group analysis demonstrated significantly reduced activation in the TBI group in both single task conditions in the occipital and posterior cingulate cortices, and for the visual task also in the thalami. This pattern was reversed in the dual task condition with significantly increased activation of a predominantly left lateralized prefrontal-anterior midline-parietal network in the TBI group compared to the controls. The increase in activation occurred within regions described to be engaged in healthy volunteers as dual task cost increases. This finding points to substitution, functional reorganization within the primary network subserving the task, following TBI, and demonstrates more effortful processing. Recruitment of these additional prefrontal resources may be connected to serial rather than parallel processing in low level dual tasking in TBI. Thus, in severe TBI, low level dual task performance depends on increased attentional and executive guidance.

Automatization and working memory capacity in schizophrenia

Working memory (WM) dysfunction in schizophrenia is characterized by inefficient WM recruitment and reduced capacity, but it is not yet clear how these relate to one another. In controls practice of certain cognitive tasks induces automatization, which is associated with reduced WM recruitment and increased capacity of concurrent task performance. We therefore investigated whether inefficient function and reduced capacity in schizophrenia was associated with a failure in automatization. FMRI data was acquired with a verbal WM task with novel and practiced stimuli in 18 schizophrenia patients and 18 controls. Participants performed a dual-task outside the scanner to test WM capacity. Patients showed intact performance on the WM task, which was paralleled by excessive WM activity. Practice improved performance and reduced WM activity in both groups. The difference in WM activity after practice predicted performance cost in controls but not in patients. In addition, patients showed disproportionately poor dual-task performance compared to controls, especially when processing information that required continuous adjustment in WM. Our findings support the notion of inefficient WM function and reduced capacity in schizophrenia. This was not related to a failure in automatization, but was evident when processing continuously changing information. This suggests that inefficient WM function and reduced capacity may be related to an inability to process information requiring frequent updating.

Storage and executive components of working memory: integrating cognitive psychology and behavior genetics in the study of aging

We combined experimental cognitive and behavior genetic methods to investigate storage and executive components of working memory in 663 middle-aged male twins. A single latent factor model indicated that digits forward (storage) and two-digit transformation (executive + storage) scores were influenced by the same genes. Additional executive demands in digit transformation appeared to increase the variance of individual genetic differences from 25% for digits forward to 48% and 53% for the digit transformation scores. Although it was not the best model, a two-factor model also provided a good fit to the data. This model suggested the possibility of a second set of genes specifically influencing the executive component. We discuss the findings in the context of research suggesting that new genetic influences come into play if demand continues to increase beyond a certain threshold, a threshold that may change with task difficulty and with age.

A decrease in brain activation associated with driving when listening to someone speak

Behavioral studies have shown that engaging in a secondary task, such as talking on a cellular telephone, disrupts driving performance. This study used functional magnetic resonance imaging (fMRI) to investigate the impact of concurrent auditory language comprehension on the brain activity associated with a simulated driving task. Participants steered a vehicle along a curving virtual road, either undisturbed or while listening to spoken sentences that they judged as true or false. The dual-task condition produced a significant deterioration in driving accuracy caused by the processing of the auditory sentences. At the same time, the parietal lobe activation associated with spatial processing in the undisturbed driving task decreased by 37% when participants concurrently listened to sentences. The findings show that language comprehension performed concurrently with driving draws mental resources away from the driving and produces deterioration in driving performance, even when it does not require holding or dialing a phone.

Management of attentional resources in within-modal and cross-modal divided attention tasks: an fMRI study

In the present study, we were interested in distinguishing the cortical representations of within-modal and cross-modal divided attention tasks by using functional magnetic resonance imaging. Sixteen healthy male subjects aged between 21 and 30 years underwent two within-modal (auditory/auditory, visual/visual) and one cross-modal (auditory/visual) divided attention task, as well as related selective attention control conditions. After subtraction of the corresponding control task the three divided attention tasks, irrespective of sensory modality, revealed significant activation in a predominantly right hemisphere network involving the prefrontal cortex, the inferior parietal cortex, and the claustrum. Under the cross-modal condition, however, the frontal and parietal activation was more extended and more bilateral and there also was stronger right hemisphere activation of the anterior cingulate cortex and the thalamus. In comparison to the within-modal conditions additional bilateral frontal and left inferior parietal activation was found for the cross-modal condition. The supplementary fronto-parietal, anterior cingulate cortex, and thalamus activation in the auditory/visual condition could be argued to reflect an additional demand for coordination of two ongoing cross-modal cognitive processes.

Neural correlates of working memory performance in adolescents and young adults with dyslexia

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.

Control processes in verbal working memory: an event-related potential study

Event-related potentials (ERPs) were recorded using a large electrode array while subjects engaged in tasks designed to dissociate control from storage/maintenance processes in verbal working memory (WM). Increased ERP negativity (450-900 ms post-stimulus onset) over left frontal regions emerged only when required dynamic updating/revision of WM stores was initiated, with augmentation of right frontal negativity in the same epoch relative to more general overall task demands. Increased ERP positivity in a similar time window over parietal regions reflected initiation of required rehearsal/maintenance of memory set contents, with progressive amplitude increases with repeated dynamic updating/revision of memory stores, suggesting increased effortful activity to resist proactive interference effects. These findings are consistent with a left frontal-parietal network for process control in verbal working memory.

Metabolic correlates of executive dysfunction

This study was designed to examine the correlations between resting-state brain glucose metabolism (CMRglc), as measured with Positron Emission Tomography and performance on executive function tasks in Alzheimer's disease (AD), while taking into account the severity of cognitive deterioration. We addressed this issue in 50 AD patients, classified as very mild (n = 22) and mild (n = 28) AD on the basis of an extensive neuropsychological battery. Thirteen healthy subjects were selected as controls for the neuropsychological measures. Statistical Parametric Mapping (SPM) was used to examine voxel-wise correlations between CMRglc and scores on selected cognitive tests of executive functions: the Stroop Test, the Trail Making Test, the Dual Task and the Phonemic Fluency, while correcting for age and global CMRglc. All analyses were done separately for the two AD subgroups. The very mild AD patients showed significant associations between Stroop and Trail Making Test scores and prefrontal regions metabolism, whereas the mild AD patients exhibited more widely distributed cognitive-metabolic correlations extending to the posterior brain regions. These data suggest that a large cortical network is implicated in executive dysfunction in AD, and that the pattern of cognitive-metabolic correlations varies according to disease severity.

Volitional control of attention and brain activation in dual task performance

This study used functional MRI (fMRI) to examine the neural effects of willfully allocating one's attention to one of two ongoing tasks. In a dual task paradigm, participants were instructed to focus either on auditory sentence comprehension, mental rotation, or both. One of the major findings is that the distribution of brain activation was amenable to strategic control, such that the amount of activation per task was systematically related to the attention-dividing instructions. The activation in language processing regions was lower when attending to mental rotation than when attending to the sentences, and the activation in visuospatial processing regions was lower when attending to sentences than when attending to mental rotations. Additionally, the activation was found to be underadditive, with the dual-task condition eliciting less activation than the sum of the attend sentence and attend rotation conditions. We also observed a laterality shift across conditions within language-processing regions, with the attend sentence condition showing bilateral activation, while the dual task condition showed a left hemispheric dominance. This shift suggests multiple language-processing modes and may explain the underadditivity in activation observed in the current and previous studies.

The nature of individual differences in working memory capacity: active maintenance in primary memory and controlled search from secondary memory

Studies examining individual differences in working memory capacity have suggested that individuals with low working memory capacities demonstrate impaired performance on a variety of attention and memory tasks compared with individuals with high working memory capacities. This working memory limitation can be conceived of as arising from 2 components: a dynamic attention component (primary memory) and a probabilistic cue-dependent search component (secondary memory). This framework is used to examine previous individual differences studies of working memory capacity, and new evidence is examined on the basis of predictions of the framework to performance on immediate free recall. It is suggested that individual differences in working memory capacity are partially due to the ability to maintain information accessible in primary memory and the ability to search for information from secondary memory.

Decreased activation of anterior cingulate cortex in the working memory of the elderly

We examined aging effects on activation in the anterior cingulate cortex during a verbal working memory using functional magnetic resonance imaging. Ten young (mean age 25 years) and 10 elderly (mean age 69 years) healthy adults performed the reading span test in which performance reflects individual differences in verbal working memory. We found an age-related difference in executive function in the prefrontal cortex; younger participants showed significant anterior cingulate cortex activation whereas the elderly did not. We found that the anterior cingulate cortex plays a critical role in executive function related to working memory. We found that behavioral deficits in verbal working memory because of aging result from the deterioration of cognitive control owing to decreased activation of the anterior cingulate cortex.

Task-related temporal and topographical changes of cortical activity during ultra-rapid visual categorization

The aim of our study was to provide electrophysiological evidence about the modulation of the categorization process by task requirements in the human brain. Event-related potentials (ERP) were recorded during three different categorization tasks using matched stimulus sets. In all cases, the subjects were required to differentiate between "animal" and "non-animal" stimuli. In the first task (two-choice task), they were asked to press corresponding buttons to each stimulus types. The second task was a go/no-go paradigm, only animal stimuli required motor response. The third task was a counting task; participants had to count the animal stimuli without any motor response. The reaction times in the go/no-go paradigm were significantly shorter. ERP differences between animal and non-animal pictures in the go/no-go task also appeared earlier and were localized at more posterior scalp positions compared to the two-choice task. Comparing animal responses in the two-choice task and in the go/no-go paradigm, we found a significant difference in the 130- to 170-ms time window over the fronto-central, centro-parietal regions. Similar differences were found between the responses to animal pictures in the two-choice task and in the counting paradigm. We used brain electric source analysis (BESA) algorithm on difference waves to localize the best fitting dipoles and determine the localization of brain areas contributing to scalp potential differences. The results show that different task requirements evoke different activity in the medial part of the temporal pole. The data we provided here draw attention to the careful handling of results obtained from categorization experiments, because different task requirements can affect the early categorization process itself.

Central executive system impairment in traumatic brain injury

PRIMARY OBJECTIVE

This study investigated whether cognitive impairment after traumatic brain injury (TBI) can be considered a consequence of (1) a speed processing deficit or (2) an impairment of the Central Executive System (CES) of working memory.

METHODS AND PROCEDURES

Thirty-seven TBI patients underwent a standardized battery of neuropsychological tests evaluating speed processing, sustained attention, short-term memory, working memory, divided attention, executive functions and long-term memory.

MAIN OUTCOMES AND RESULTS

Patients showed severe deficits in working memory, divided attention, executive functions and long-term memory. Divided attention, long-term memory and executive functions deficits significantly correlated with working memory, but not with speed processing deficits. Moreover, multiple regression analyses showed that a CES impairment and not a speed processing deficit predicted divided attention, executive functions and long-term memory deficits. The severity and the site of brain lesions did not predict the level of CES or speed processing impairment.

CONCLUSIONS

The cognitive impairment following TBI seem to be caused by an impairment of the Central Executive System, rather than a speed processing deficit.

Alcohol attentional bias: drinking salience or cognitive impairment?

OBJECTIVE

This study evaluated whether alcohol attentional bias is an artifact of excessive drinkers' impaired cognitive functioning, which adversely affects their performance on the classic Stroop test (a measure of inhibitory control) and the Shipley Institute of Living Scale (SILS; a measure of verbal and abstraction ability). Both tests measure aspects of executive cognitive functioning (ECF).

METHODS

Social drinkers (N=87) and alcohol-dependent drinkers (N=47) completed a measure of alcohol consumption, classic and alcohol-related Stroop tests, and the SILS.

RESULTS

A multivariate analysis of variance (MANOVA) showed that the dependent drinkers were poorer on the cognitive measures (SILS scores and classic Stroop interference) and had greater alcohol attentional bias than the social drinkers. An analysis of covariance (ANCOVA) in which the cognitive measures were controlled showed that the dependent drinkers' greater alcohol attentional bias was not an artifact of their poorer cognitive performance.

CONCLUSION

The results are discussed in terms of cognitive-motivational models, which suggest that excessive drinking sensitizes alcohol abusers' attentional responsiveness to alcohol-related stimuli to a degree that exceeds the adverse effects of alcohol on their general cognitive functioning.

Neural correlates of superior intelligence: stronger recruitment of posterior parietal cortex

General intelligence (g) is a common factor in diverse cognitive abilities and a major influence on life outcomes. Neuroimaging studies in adults suggest that the lateral prefrontal and parietal cortices play a crucial role in related cognitive activities including fluid reasoning, the control of attention, and working memory. Here, we investigated the neural bases for intellectual giftedness (superior-g) in adolescents, using fMRI. The participants consisted of a superior-g group (n = 18, mean RAPM = 33.9 +/- 0.8, >99%) from the national academy for gifted adolescents and the control group (n = 18, mean RAPM = 22.8 +/- 1.6, 60%) from local high schools in Korea (mean age = 16.5 +/- 0.8). fMRI data were acquired while they performed two reasoning tasks with high and low g-loadings. In both groups, the high g-loaded tasks specifically increased regional activity in the bilateral fronto-parietal network including the lateral prefrontal, anterior cingulate, and posterior parietal cortices. However, the regional activations of the superior-g group were significantly stronger than those of the control group, especially in the posterior parietal cortex. Moreover, regression analysis revealed that activity of the superior and intraparietal cortices (BA 7/40) strongly covaried with individual differences in g (r = 0.71 to 0.81). A correlated vectors analysis implicated bilateral posterior parietal areas in g. These results suggest that superior-g may not be due to the recruitment of additional brain regions but to the functional facilitation of the fronto-parietal network particularly driven by the posterior parietal activation.

Right parietal contributions to verbal working memory: spatial or executive?

The left inferior parietal cortex has been claimed to be the site of the verbal short-term store, yet imaging studies report activity of a homologous right-hemisphere region in verbal working memory tasks as well. In spite of its prevalent activity, right parietal contributions to verbal working memory are poorly understood. To clarify its role in verbal working memory performance, we tested a patient with a lesion in the right parietal lobe on verbal and spatial versions of the N-back task. The patient was impaired in all the spatial conditions regardless of load (0-, 1-, and 2-back), whereas in the verbal N-back he was impaired only in the conditions with a memory demand (1- and 2-back). Given that we had presented stimuli at multiple locations in the verbal N-back, however, it remained possible that the lesion impaired spatial representation rather than verbal working memory per se. With central stimulus presentation, his performance dramatically improved indicating that his difficulty with the N-back task was largely due to his poor visuospatial abilities.

Differential Anterior Prefrontal Activation during the Recognition Stage of a Spatial Working Memory Task

Neuroimaging studies commonly show widespread activations in the prefrontal cortex during various forms of working memory and long-term memory tasks. However, the anterior prefrontal cortex (aPFC, Brodmann area 10) has been mainly associated with retrieval in episodic memory, and its role in working memory is less clear. We conducted an event-related functional magnetic resonance imaging study to examine brain activations in relation to recognition in a spatial delayed-recognition task. Similar to the results from previous findings, several frontal areas were strongly activated during the recognition phase of the task, including the aPFC, the lateral PFC and the anterior cingulate cortex. Although the aPFC was more active during the recognition phase, it was also active during the delay phase of the spatial working memory task. In addition, the aPFC showed greater activity in response to negative probes (non-targets) than to positive probes (targets). While our analyses focused on examining signal changes in the aPFC, other prefrontal regions showed similar effects and none of the areas were more active in response to the positive probes than to the negative probes. Our findings support the conclusion that the aPFC is involved in working memory and particularly in processes that distinguish target and non-target stimuli during recognition.

Parieto-premotor Areas Mediate Directional Interference During Bimanual Movements

In bimanual movements, interference emerges when limbs are moved simultaneously along incompatible directions. The neural substrate and mechanisms underlying this phenomenon are largely unknown. We used functional magnetic resonance imaging to compare brain activation during directional incompatible versus compatible bimanual movements. Our main results were that directional interference emerges primarily within superior parietal, intraparietal and dorsal premotor areas of the right hemisphere. The same areas were also activated when the unimanual subtasks were executed in isolation. In light of previous findings in monkeys and humans, we conclude that directional interference activates a parieto-premotor circuit that is involved in the control of goal-directed movements under somatosensory guidance. Moreover, our data suggest that the parietal cortex might represent an important locus for integrating spatial aspects of the limbs' movements into a common action. It is hypothesized to be the candidate structure from where interference arises when directionally incompatible movements are performed. We discuss the possibility that interference emerges when computational resources in these parietal areas are insufficient to code two incompatible movement directions independently from each other.

Cooperation of the anterior cingulate cortex and dorsolateral prefrontal cortex for attention shifting

Attention shifting in the working memory system plays an important role in goal-oriented behavior, such as reading, reasoning, and driving, because it involves several cognitive processes. This study identified brain activity leading to individual differences in attention shifting for dual-task performance by using the group comparison approach. A large-scale pilot study was initially conducted to select suitable good and poor performers. The fMRI experiment consisted of a dual-task condition and two single-task conditions. Under the dual-task condition, participants verified the status of letters while concurrently retaining arrow orientations. The behavioral results indicated that accuracy in arrow recognition was better in the good performers than in the poor performers under the dual-task condition but not under the single-task condition. Dual-task performance showed a positive correlation with mean signal change in the right anterior cingulate cortex (ACC) and right dorsolateral prefrontal cortex (DLPFC). Structural equation modeling indicated that effective connectivity between the right ACC and right DLPFC was present in the good performers but not in the poor performers, although activations of the task-dependent posterior regions were modulated by the right ACC and right DLPFC. We conclude that individual differences in attention shifting heavily depend on the functional efficiency of the cingulo-prefrontal network.

Cross-modal temporal order memory for auditory digits and visual locations: an fMRI study

A function of working memory is to remember the temporal sequence of events, often occurring across different sensory modalities. To study the neural correlates of this function, we conducted an event-related functional magnetic resonance imaging (fMRI) experiment with a cross-modal memory task. Subjects were required to recall auditory digits and visual locations either in mixed order (cross-modality) or in separate order (within-modality). To identify the brain regions involved in the memory of cross-modal temporal order, we compared the blood oxygenation level-dependent (BOLD) response between the mixed and the separate order tasks. As a control, cortical areas sensitive to the memory load were mapped by comparing the 10-item condition with the 6-item condition in the separate order task. Results show that the bilateral prefrontal, right premotor, temporo-parietal junction (TPJ) and left superior parietal cortices had significantly more activation in the mixed task than in the separate task. Some of these areas were also sensitive to the memory load, whereas the right prefrontal cortex and TPJ were relatively more sensitive to the cross-modal order but not the memory load. Our study provides potential neural correlates for the episodic buffer, a key component of working memory as proposed previously [Baddeley. Trends Cogn Sci 2000;4:417-423].

Neural substrates associated with the concurrent performance of dual working memory tasks

The neural substrates of the dual working memory (WM) process were investigated using concurrent performance of auditory and visual n-back WM tasks. Based on the pre-fMRI behavioral testing, a lettered 1-back WM paradigm was implemented for an fMRI examination of healthy volunteers who performed (1) auditory, (2) visual, and (3) simultaneous visual and auditory WM tasks. The behavioral performance, as measured by the reaction time, was deteriorated in the dual task condition compared to the single task condition. Group analysis of the fMRI data revealed that the majority of activation identified during each component task was concurrently activated in the dual task condition. However, several neural substrates such as left middle frontal gyrus, left superior parietal lobule, posterior aspect of right inferior temporal gyrus, and bilateral parahippocampal gyri were selectively activated during the dual WM task. These data suggest that new neural networks come into play to assist in the greater load placed on the WM with the incongruent stimulation modality, which may also have implications in crossmodal integrative processes.

Functional roles of the cingulo-frontal network in performance on working memory

We examined the relationship between brain activities and task performance on working memory. A large-scale study was initially administered to identify good and poor performers using the operation span and reading span tasks. On the basis of those span scores, we divided 20 consenting participants into high- and low-span groups. In an fMRI study, the participants performed verification of arithmetic problems and retention of target words either concurrently or separately. The behavioral results showed that performance was better in the high-span group than in the low-span group under a dual-task condition, but not under two single-task conditions. The anterior cingulate cortex (ACC), left prefrontal cortex (PFC), left inferior frontal cortex, and bilateral parietal cortex were primarily activated for both span groups. We found that signal changes in the ACC were greater in the high-span group than in the low-span group under the dual-task condition, but not under the single-task conditions. Structural equation modeling indicated that an estimate of effective connectivity from the ACC to the left PFC was positive for the high-span group and negative for the-low span group, suggesting that closer cooperation between the two brain regions was strongly related to working memory performance. We conclude that central executive functioning for attention shifting is modulated by the cingulo-frontal network.

Demands on Finite Cognitive Capacity Cause Infants' Perseverative Errors

This research unites traditionally disparate developmental domains-cognition and locomotion-to examine the classic cognitive issue of the development of inhibition in infancy. In 2 locomotor A-not-B tasks, 13-month-old walking infants inhibited a prepotent response under low task demands (walking on flat ground), but perseverated under increased task demands (descending a staircase). Despite elimination of factors previously associated with infant perseveration, infants still perseverated in the difficult stairs condition. Increasing cognitive load by manipulating task difficulty affected infants' ability to inhibit repeated responses that were no longer appropriate. Evidence supports a cognitive capacity account of infant perseveration, in which infants' performance depends on allocation of cognitive and attentional resources.

Co-ordination within and between verbal and visuospatial working memory: network modulation and anterior frontal recruitment

Attention switching between items being stored and manipulated in working memory (WM) is proposed to be an elementary executive function. Experiment 1 reveals a similar attentional limitation within and between verbal and visuospatial WM and identifies a supramodal switching process required for switching between WM items. By using functional magnetic resonance imaging, Experiment 2 investigated brain activation correlates of parametrically varied attention switching within and between these two WM modalities. Attention switching activation was broadly distributed, was quite similar across the three conditions, and, in almost all areas, increased with increasing switching demand, indicating that attention switching recruits and modulates the entire WM network. Dorsolateral prefrontal cortex was implicated in both within- and between-modality attention switching, but no significant activation was found in ventrolateral areas, supporting dorsal-ventral process models of prefrontal organization. A functional dissociation between anterior frontal and dorsolateral prefrontal cortex was found with the former being more activated when switching attention between modalities was required. The data challenge the notion of an anatomically separate attention switching executive function, but suggest that anterior frontal areas are recruited for the additional demand of coordinating the verbal and visuospatial WM slave systems.

Neural correlates of thought suppression

The present report used functional magnetic resonance imaging (fMRI) to examine the neural correlates of thought suppression. Subjects were imaged while alternately (i) attempting to suppress a particular thought, (ii) attempting to suppress all thoughts, or (iii) thinking freely about any thought. Suppression of a particular thought, when compared to the free-thought control condition, revealed greater activation in the anterior cingulate. When the task of suppressing all conscious thoughts was compared to free-thought, a more distributed network of brain regions, including the anterior cingulate and the insula, was activated. These findings are consistent with previous research on cognitive control and may provide potential insights into psychological disorders involving recurring, intrusive thoughts.

The roles of the cerebellum and basal ganglia in timing and error prediction

Recent evidence that the cerebellum and the basal ganglia are activated during the performance of cognitive and attention tasks challenges the prevailing view of their primary function in motor control. The specific roles of the basal ganglia and the cerebellum in cognition, however, have been difficult to identify. At least three functional hypotheses regarding their roles have been proposed. The first hypothesis suggests that their main function is to switch attentional set. The second hypothesis states that they provide error signals regarding stimuli or rewards. The third hypothesis is that they operate as an internal timing system, providing a precise representation of temporal information. Using functional magnetic resonance imaging, we tested these three hypotheses using a task-switching experiment with a 2 x 2 factorial design varying timing (random relative to fixed) and task order (unpredictable relative to predictable). This design allowed us to test whether switching between tasks, timing irregularity and/or task order unpredictability activate the basal ganglia and/or the cerebellum. We show that the cerebellum is primarily activated with timing irregularity while the anterior striatum is activated with task order unpredictability, supporting their distinctive roles in two forms of readjustment. Task order unpredictability alone, independent of reward delivery, is sufficient to induce striatal activation. In addition, activation of the cerebellum and basal ganglia were not specific to switching attention because these regions were both activated during switching between tasks and during the simultaneous maintenance of two tasks without switching between them.

Specialization in the left prefrontal cortex for sentence comprehension

Using functional magnetic resonance imaging (fMRI), we examined cortical activation under syntactic decision tasks and a short-term memory task for sentences, focusing on essential properties of syntactic processing. By comparing activation in these tasks with a short-term memory task for word lists, we found that two regions in the left prefrontal cortex showed selective activation for syntactic processing: the dorsal prefrontal cortex (DPFC) and the inferior frontal gyrus (IFG). Moreover, the left DPFC showed more prominent activation under the short-term memory task for sentences than that for word lists, which cannot be explained by general cognitive factors such as task difficulty and verbal short-term memory. These results support the proposal of specialized systems for sentence comprehension in the left prefrontal cortex.

Posterior parietal cortex is implicated in continuous switching between verbal fluency tasks: an fMRI study with clinical implications

We investigated whether posterior parietal cortex controls attentional switching when the tasks involve neither spatial nor visual cognition. Normal volunteers were scanned using functional MRI (fMRI). In all conditions, subjects were required to covertly produce words in verbal fluency tasks. They did so at a rate of one every 2 s (with eyes closed) in response to an auditory beep. In the non-switching (NS) trials, subjects responded with a series of items from a prespecified semantic category (SC) (e.g. fruits or cars) and from overlearned sequences (OSs) (days of the week, months of the year or letters of the alphabet). Instructions as to which category items should be drawn from on a given run of trials were presented over fMRI-compatible earphones prior to each run. In the switching (S) trials, subjects produced a series of word triads from three SCs: for example, fruits, cars and furniture (e.g. pear, Mercedes, table.); and from three OSs: days of the week, months of the year and letters of the alphabet (e.g. Monday, January, A.). This design is factorial, with the factors verbal class (SC or OSs) and switching conditions (S or NS). Increases in neural activity (P < 0.05, corrected for multiple comparisons) were observed only in superior posterior parietal cortex bilaterally as a main effect of the S conditions compared with the NS conditions. When SC fluency was compared with OS fluency, significant activations were found in anterior cingulate cortex bilaterally, the left inferior frontal gyrus, the middle frontal gyrus bilaterally, frontal operculum bilaterally and in the cerebellar vermis. These results support the hypothesis that superior posterior parietal cortex is a supramodal area implicated in task switching, even when no visual or spatial component is implicated in the tasks. Task switching, frequently used to examine 'frontal' executive functions, may also be clinically relevant to the assessment of patients with superior posterior parietal lesions.

Integration of emotion and cognition in the lateral prefrontal cortex

We used functional MRI to test the hypothesis that emotional states can selectively influence cognition-related neural activity in lateral prefrontal cortex (PFC), as evidence for an integration of emotion and cognition. Participants (n = 14) watched short videos intended to induce emotional states (pleasant/approach related, unpleasant/withdrawal related, or neutral). After each video, the participants were scanned while performing a 3-back working memory task having either words or faces as stimuli. Task-related neural activity in bilateral PFC showed a predicted pattern: an Emotion x Stimulus crossover interaction, with no main effects, with activity predicting task performance. This highly specific result indicates that emotion and higher cognition can be truly integrated, i.e., at some point of processing, functional specialization is lost, and emotion and cognition conjointly and equally contribute to the control of thought and behavior. Other regions in lateral PFC showed hemispheric specialization for emotion and for stimuli separately, consistent with a hierarchical and hemisphere-based mechanism of integration.

The role of frontopolar cortex in subgoal processing during working memory

Neuroimaging studies have implicated the anterior-most or frontopolar regions of prefrontal cortex (FP-PFC, e.g., Brodmann's Area 10) as playing a central role in higher cognitive functions such as planning, problem solving, reasoning, and episodic memory retrieval. The current functional magnetic resonance imaging (fMRI) study tested the hypothesis that FP-PFC subserves processes related to the monitoring and management of subgoals, while maintaining information in working memory (WM). Subjects were scanned while performing two variants of a simple delayed response WM task. In the control WM condition, subjects monitored for the presence of a specific concrete probe word (LIME) occurring following a specific abstract cue word (FATE). In the subgoal WM condition, subjects monitored for the presence of any concrete probe word immediately following any abstract cue word. Thus, the task required semantic classification of the probe word (the subgoal task), while the cue was simultaneously maintained in WM, so that both pieces of information could be integrated into a target determination. In a second control condition, subjects performed abstract/concrete semantic classification without WM demands. A region within right FP-PFC was identified which showed significant activation during the subgoal WM condition, but no activity in either of the two control conditions. However, this FP-PFC region was not modulated by direct manipulation of active maintenance demands. In contrast, left dorsolateral PFC was affected by active maintenance demands, but the effect did not interact with the presence of a subgoal task. Finally, left ventral PFC regions showed activation in response to semantic classification, but were not affected by WM demands. These results suggest a triple dissociation of function within PFC regions, and further indicate that FP-PFC is selectively engaged by the requirement to monitor and integrate subgoals during WM tasks.