Neural activity during attention shifts between object features

Proteomic association with age-dependent sex differences in Wisconsin Card Sorting Test performance in healthy Thai subjects

Sex differences in cognitive function exist, but they are not stable and undergo dynamic change during the lifespan. However, our understanding of how sex-related neural information transmission evolves with age is still in its infancy. This study utilized the Wisconsin Card Sorting Test (WCST) and the label-free proteomics method with bioinformatic analysis to investigate the molecular mechanisms underlying age-related sex differences in cognitive performance in 199 healthy Thai subjects (aged 20-70 years), as well as explore the sex-dependent protein complexes for predicting cognitive aging. The results showed that males outperformed females in two of the five WCST sub-scores: %Corrects and %Errors. Sex differences in these scores were related to aging, becoming noticeable in those over 60. At the molecular level, differently expressed individual proteins and protein complexes between both sexes are associated with the potential N-methyl-D-aspartate type glutamate receptor (NMDAR)-mediated excitotoxicity, with the NMDAR complex being enriched exclusively in elderly female samples. These findings provided a preliminary indication that healthy Thai females might be more susceptible to such neurotoxicity, as evidenced by their cognitive performance. NMDAR protein complex enrichment in serum could be proposed as a potential indication for predicting cognitive aging in healthy Thai females.

Cholinergic-estrogen interaction is associated with the effect of education on attenuating cognitive sex differences in a Thai healthy population

The development of human brain is shaped by both genetic and environmental factors. Sex differences in cognitive function have been found in humans as a result of sexual dimorphism in neural information transmission. Numerous studies have reported the positive effects of education on cognitive functions. However, little work has investigated the effect of education on attenuating cognitive sex differences and the neural mechanisms behind it based on healthy population. In this study, the Wisconsin Card Sorting Test (WCST) was employed to examine sex differences in cognitive function in 135 Thai healthy subjects, and label-free quantitative proteomic method and bioinformatic analysis were used to study sex-specific neurotransmission-related protein expression profiles. The results showed sex differences in two WCST sub-scores: percentage of Total corrects and Total errors in the primary education group (Bayes factor>100) with males performed better, while such differences eliminated in secondary and tertiary education levels. Moreover, 11 differentially expressed proteins (DEPs) between men and women (FDR<0.1) were presented in both education groups, with majority of them upregulated in females. Half of those DEPs interacted directly with nAChR3, whereas the other DEPs were indirectly connected to the cholinergic pathways through interaction with estrogen. These findings provided a preliminary indication that a cholinergic-estrogen interaction relates to, and might underpin, the effect of education on attenuating cognitive sex differences in a Thai healthy population.

Age-related decline in cognitive flexibility in female chimpanzees

Data on cognitive aging in chimpanzees are extremely sparse, yet can provide an invaluable phylogenetic perspective, especially because Alzheimer disease (AD)-like neuropathology has recently been described in the oldest chimpanzee brains. This finding underscores the importance of data on cognitive aging in this fellow hominin, our closest biological relative. We tested 30 female chimpanzees, 12-56 years old, on a computerized analog of the Wisconsin Card Sort test. This test assesses cognitive flexibility, which is severely impaired in normal aging and AD. Subjects selected stimuli according to color or shape; the rewarded dimension (i.e., color or shape) switched without warning and the chimpanzee had to adapt her responses accordingly. We found that increasing age was associated with an increased number of perseverative errors and an increased number of trials to reach criterion in each switching dimension. The number of aborted trials was similar across age groups. These data show that similar to humans, chimpanzees show a clear age-related decline in cognitive flexibility that is already observed at middle age.

Cognitive persistence: Development and validation of a novel measure from the Wisconsin Card Sorting Test

The Wisconsin Card Sorting Test (WCST) has long been used as a neuropsychological assessment of executive function abilities, in particular, cognitive flexibility or "set-shifting". Recent advances in scoring the task have helped to isolate specific WCST performance metrics that index set-shifting abilities and have improved our understanding of how prefrontal and parietal cortex contribute to set-shifting. We present evidence that the ability to overcome task difficulty to achieve a goal, or "cognitive persistence", is another important prefrontal function that is characterized by the WCST and that can be differentiated from efficient set-shifting. This novel measure of cognitive persistence was developed using the WCST-64 in an adult lifespan sample of 230 participants. The measure was validated using individual variation in cingulo-opercular cortex function in a sub-sample of older adults who had completed a challenging speech recognition in noise fMRI task. Specifically, older adults with higher cognitive persistence were more likely to demonstrate word recognition benefit from cingulo-opercular activity. The WCST-derived cognitive persistence measure can be used to disentangle neural processes involved in set-shifting from those involved in persistence.

Neurocomputational Nosology: Malfunctions of Models and Mechanisms

Executive dysfunctions, psychopathologies arising from problems in the control and regulation of behavior, can occur as a result of the faulty execution of formal information processing models or as a result of malfunctioning neural mechanisms. The models correspond to the formal descriptions of how signals in the environment must be transformed in order to behave adaptively, and the mechanisms correspond to the signal transformations that nervous systems implement in order to execute those cognitive functions. Mechanisms in the form of repeated patterns of neural dynamics execute information processing models. Two distinct modes of malfunction can occur when neural dynamics execute models of information processing. The processing models describing behavior may fail to be executed correctly by neural mechanisms. Or, the neural mechanisms may malfunction, failing to implement the right computation. As an example of malfunctioning models in executive cognition, purported failures of rule following can be understood as failures to appropriately execute a suite of processing models. As an example of malfunctioning mechanisms of executive cognition, maladaptive behavior resulting from dysfunction in the medial prefrontal cortex (mPFC) can be understood as failures in the signal transformations carried out therein. The purpose of these examples is to illustrate the potential benefits of considering models and mechanisms in the diagnosis and etiology of neuropsychological illness and dysfunction, especially disorders of executive cognition.

Neural Correlates of Visuomotor Learning in Autism

Motor impairments are prevalent in children with autism spectrum disorder. The Serial Reaction Time Task, a well-established visuomotor sequence learning probe, has produced inconsistent behavioral findings in individuals with autism. Moreover, it remains unclear how underlying neural processes for visuomotor learning in children with autism compare to processes for typically developing children. Neural activity differences were assessed using functional magnetic resonance imaging during a modified version of the Serial Reaction Time Task in children with and without autism. Though there was no group difference in visuomotor sequence learning, underlying patterns of neural activation significantly differed when comparing sequence (i.e., learning) to random (i.e., nonlearning) blocks. Children with autism demonstrated decreased activity in brain regions implicated in visuomotor sequence learning: superior temporal sulcus and posterior cingulate cortex. The findings implicate differences in brain mechanisms that support initial sequence learning in autism and can help explain behavioral observations of autism-associated impairments in skill development (motor, social, communicative) reliant on visuomotor integration.

Different Neural Mechanisms Underlie Deficits in Mental Flexibility in Post-Traumatic Stress Disorder Compared to Mild Traumatic Brain Injury

Mental flexibility is a core executive function that underlies the ability to adapt to changing situations and respond to new information. Individuals with post-traumatic stress disorder (PTSD) and mild traumatic brain injury (mTBI) complain of a number of executive function difficulties, one of which is mental inflexibility or an inability to switch between concepts. While the behavioral presentation of mental inflexibility is similar in those with PTSD or mTBI, we hypothesized that the differences in their etiology would manifest as differences in their underlying brain processing. The neural substrates of mental flexibility have been examined with a number of neuroimaging modalities. Functional magnetic resonance imaging has elucidated the brain regions involved, whereas electroencephalography has been applied to understand the timing of the brain activations. Magnetoencephalography, with its high temporal and spatial resolution, has more recently been used to delineate the spatiotemporal progression of brain processes involved in mental flexibility and has been applied to the study of clinical populations. In a number of separate studies, our group has compared the source localization and brain connectivity during a mental flexibility set-shifting task in a group of soldiers with PTSD and civilians with an acute mTBI. In this article, we review the results from these studies and integrate the data between groups to compare and contrast differences in behavioral, neural, and connectivity findings. We show that the different etiologies of PTSD and mTBI are expressed as distinct neural profiles for mental flexibility that differentiate the groups despite their similar clinical presentations.

Cardiovascular biomarkers and carotid IMT scores as predictors of cognitive function

OBJECTIVE

Multiple cardiovascular risk factors are associated with early cognitive decline. Measures of complex information processing provide one of the earliest signs of cognitive decline and appear related to arterial plaque growth. The purpose of this study was to determine how cardiovascular risk factors and carotid intima-media thickness (IMT) scores are associated with cognitive function and complex information processing scores.

METHODS

This study used a retrospective, cross-sectional analysis of 536 men and women attending an executive evaluation program. Measurements were made of body composition, cardiovascular status, fitness and diet, and laboratory measures, including carotid IMT. Each subject was tested with a computerized neurocognitive test battery.

RESULTS

Complex information processing (CIP), also called executive function, is independently related to carotid IMT scores (p < 0.01), as are other cardiovascular biomarkers, including aerobic capacity fiber, B12, and long-chain n-3 fatty acid intake (p < 0.01 for each). However, after controlling for carotid IMT, only IMT showed a significant relationship with CIP scores.

CONCLUSIONS

Carotid IMT scores are the strongest independent cardiovascular biomarker for cognitive function, especially complex information processing. Greater intake of fiber, long-chain n-3 fatty acids (N3FAs), and vitamin B12, as well as measures of aerobic fitness, is associated with enhanced cognitive function, yet controlling for IMT scores diminished their association. Because decreasing CIP scores are linearly associated with cognitive decline, future randomized clinical trials that yield improvements in carotid IMT scores should also assess for changes in cognitive function.

Staying responsive to the world: modality-specific and -nonspecific contributions to speeded auditory, tactile, and visual stimulus detection

Sustained responsiveness to external stimulation is fundamental to many time-critical interactions with the outside world. We used functional magnetic resonance imaging during speeded stimulus detection to identify convergent and divergent neural correlates of maintaining the readiness to respond to auditory, tactile, and visual stimuli. In addition, using a multimodal condition, we investigated the effect of making stimulus modality unpredictable. Relative to sensorimotor control tasks, all three unimodal detection tasks elicited stronger activity in the right temporo-parietal junction, inferior frontal cortex, anterior insula, dorsal premotor cortex, and anterior cingulate cortex as well as bilateral mid-cingulum, midbrain, brainstem, and medial cerebellum. The multimodal detection condition additionally activated left dorsal premotor cortex and bilateral precuneus. Modality-specific modulations were confined to respective sensory areas: we found activity increases in relevant, and decreases in irrelevant sensory cortices. Our findings corroborate the modality independence of a predominantly right-lateralized core network for maintaining an alert (i.e., highly responsive) state and extend previous results to the somatosensory modality. Monitoring multiple sensory channels appears to induce additional processing, possibly related to stimulus-driven shifts of intermodal attention. The results further suggest that directing attention to a given sensory modality selectively enhances and suppresses sensory processing-even in simple detection tasks, which do not require inter- or intra-modal selection.

The Wisconsin Card Sorting Test and the cognitive assessment of prefrontal executive functions: a critical update

For over four decades the Wisconsin Card Sorting Test (WCST) has been one of the most distinctive tests of prefrontal function. Clinical research and recent brain imaging have brought into question the validity and specificity of this test as a marker of frontal dysfunction. Clinical studies with neurological patients have confirmed that, in its traditional form, the WCST fails to discriminate between frontal and non-frontal lesions. In addition, functional brain imaging studies show rapid and widespread activation across frontal and non-frontal brain regions during WCST performance. These studies suggest that the concept of an anatomically pure test of prefrontal function is not only empirically unattainable, but also theoretically inaccurate. The aim of the present review is to examine the causes of these criticisms and to resolve them by incorporating new methodological and conceptual advances in order to improve the construct validity of WCST scores and their relationship to prefrontal executive functions. We conclude that these objectives can be achieved by drawing on theory-guided experimental design, and on precise spatial and temporal sampling of brain activity, and then exemplify this using an integrative model of prefrontal function [i.e., Miller, E. K. (2000). The prefrontal cortex and cognitive control. Nature Reviews Neuroscience, 1, 59-65.] combined with the formal information theoretical approach to cognitive control [Koechlin, E., & Summerfield, C. (2007). An information theoretical approach to prefrontal executive function. Trends in Cognitive Sciences, 11, 229-235.].

Age-related cognitive decline in patients with mood disorders

BACKGROUND

The relationship between depression and dementia is complex and appreciation of its true nature is evolving. Depression is an early symptom of dementia. Recent research suggests that mood disorders, in general, may be risk factors for the development of dementia.

METHOD

This was a cross-sectional study of the effect of aging on cognition in patients with mood disorders compared to normal controls. Patients and controls were tested with a comprehensive neurocognitive test battery, CNS Vital Signs. The question at issue was the rate of aging-related cognitive decline the same or different in mood disorder patients compared to normal controls.

SUBJECTS

455 patients with mood disorders, 336 with major depression and 119 with bipolar affective disorder, age 18-86, and 1003 normal controls, age 35-90. Normal controls were age 18 or older in the CNS Vital Signs normative database. The normal subjects were healthy, on no centrally-active medication, and free of psychiatric and neurological disorders.

RESULTS

Cognitive performance in the two groups run in parallel from age 18 to 45; they begin to diverge during the next decade; after age 65, mood disorder patients, as a group, decline more sharply than normal controls. The differential rate of decline was seen in the domains of memory, attention, processing speed and executive function.

CONCLUSIONS

There seems to be an acceleration in age-related cognitive decline in patients with depression in particular, and mood disorders in general, compared to age-matched normal controls. It is likely, then, that as people age, the ones who develop depression, or who fail to recover from early episodes of depression, include a substantial number of patients at risk for developing dementia. This is consistent with the fact that late-life depression may be an early manifestation of dementia. The data are also consistent with the idea that mood disorders are a risk factor, albeit a weak one, for the development of dementia. From a slightly different perspective, one might imagine that some pathophysiological event is shared by the mood disorders and dementing conditions.

Long-term speeding in perceptual switches mediated by attention-dependent plasticity in cortical visual processing

Binocular rivalry has been extensively studied to understand the mechanisms that control switches in visual awareness and much has been revealed about the contributions of stimulus and cognitive factors. Because visual processes are fundamentally adaptive, however, it is also important to understand how experience alters the dynamics of perceptual switches. When observers viewed binocular rivalry repeatedly over many days, the rate of perceptual switches increased as much as 3-fold. This long-term rivalry speeding exhibited a pattern of image-feature specificity that ruled out primary contributions from strategic and nonsensory factors and implicated neural plasticity occurring in both low- and high-level visual processes in the ventral stream. Furthermore, the speeding occurred only when the rivaling patterns were voluntarily attended, suggesting that the underlying neural plasticity selectively engages when stimuli are behaviorally relevant. Long-term rivalry speeding may thus reflect broader mechanisms that facilitate quick assessments of signals that contain multiple behaviorally relevant interpretations.

Medications do not necessarily normalize cognition in ADHD patients

OBJECTIVE

Although ADHD medications are effective for the behavioral components of the disorder, little information exists concerning their effects on cognition, especially in community samples.

METHOD

A cross-sectional study of ADHD patients treated with three different ADHD drugs was conducted. Patients' performance on a computerized neurocognitive screening battery was compared to untreated ADHD patients and normal controls (NML). A total of 177 ADHD patients aged 10 to 18, achieved a favorable response to one of the following medications: Adderall XR (AMP), atomoxetine (ATMX), and Concerta (MPH-OROS) compared to 95 untreated ADHD patients and 101 NML.

RESULTS

Significant differences were detected between normals and untreated ADHD patients. Treated patients performed better than untreated patients but remained significantly impaired compared to normal subjects.

CONCLUSION

Even with optimal treatment, based on parents' and teachers' opinions, subtle and not-so-subtle neurocognitive impairments persisted in the ADHD patients. Some ADHD patients may require additional educational assistance, even in the face of successful medication treatment.

Neural correlates of recollection and familiarity: A review of neuroimaging and patient data

Dual-process models of recognition memory suggest that two processes contribute to performance: recollection and familiarity. Recent work suggests that the two processes are dissociable at the level of the brain. Here we review 12 studies that used event-related functional magnetic resonance imaging (fMRI), and 21 studies of patients with damage to various brain regions, which examined recollection and familiarity using the 'Remember-Know' (R/K), process dissociation procedure (PDP), or receiver operator characteristic (ROC) memory paradigms, for insights into the neural basis of each process. Results show that recollection and familiarity are characterized by different patterns of brain activity in frontal, parietal, sensory, and medial temporal cortices. Results suggest that recollection and familiarity cannot be dissociated based on confidence levels alone, and that the two processes are not exclusive. Based on these results, we propose a model in which recollection and familiarity can be dissociated in two ways: recruitment of additional brain regions in frontal, medial temporal, and content-specific cortices during recollection, and in variations in coherence of brain networks activated during recollective- or familiarity-based processing.

An examination of executive dysfunction associated with frontostriatal circuitry in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative movement disorder presenting with subcortical pathology and characterized by motor deficits. However, as is frequently reported in the literature, patients with PD can also exhibit cognitive and behavioral (i.e., nonmotor) impairments, cognitive executive deficits and depression being the most prominent. Considerable attention has addressed the role that disruption to frontostriatal circuitry can play in mediating nonmotor dysfunction in PD. The three nonmotor frontostriatal circuits, which connect frontal cortical regions to the basal ganglia, originate from the dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC), and orbitofrontal cortex (OFC). The objective of the current study was to use our understanding of frontostriatal circuit function (via literature review) to categorize neuropsychological measures of cognitive and behavioral executive functions by circuit. To our knowledge, such an approach has not been previously attempted in the study of executive dysfunction in PD. Neuropsychological measures of executive functions and self-report behavioral inventories, categorized by circuit function, were administered to 32 nondemented patients with Parkinson's disease (NDPD) and to 29 demographically matched, healthy normal control participants (NC). Our findings revealed significant group differences for each circuit, with the PD group performing worse than the NC group. Among the patients with PD, indices of impairment were greater for tasks associated with DLPFC function than with OFC function. Further, only an index of DLPFC test performance was demonstrated to significantly discriminate individuals with and without PD. In conclusion, our findings suggest that nondemented patients with PD exhibit greater impairment on neuropsychological measures associated with DLPFC than with ACC or OFC circuit function.

Executive function and the frontal lobes: a meta-analytic review

Currently, there is debate among scholars regarding how to operationalize and measure executive functions. These functions generally are referred to as "supervisory" cognitive processes because they involve higher level organization and execution of complex thoughts and behavior. Although conceptualizations vary regarding what mental processes actually constitute the "executive function" construct, there has been a historical linkage of these "higher-level" processes with the frontal lobes. In fact, many investigators have used the term "frontal functions" synonymously with "executive functions" despite evidence that contradicts this synonymous usage. The current review provides a critical analysis of lesion and neuroimaging studies using three popular executive function measures (Wisconsin Card Sorting Test, Phonemic Verbal Fluency, and Stroop Color Word Interference Test) in order to examine the validity of the executive function construct in terms of its relation to activation and damage to the frontal lobes. Empirical lesion data are examined via meta-analysis procedures along with formula derivatives. Results reveal mixed evidence that does not support a one-to-one relationship between executive functions and frontal lobe activity. The paper concludes with a discussion of the implications of construing the validity of these neuropsychological tests in anatomical, rather than cognitive and behavioral, terms.

Event-related potential correlates of extradimensional and intradimensional set-shifts in a modified Wisconsin Card Sorting Test

Event-related potentials (ERPs) were recorded in healthy adult participants during the performance of a modified version of the Wisconsin Card Sorting Test that was designed to isolate the effects of extradimensional (ED) and intradimensional (ID) set-shifts. ERP averages were created for ED- and ID-Shift trials, as well as for the 5th trial in each block (Maintain-Rule). Differences in sensory and longer latency ERP components were found between the ED- and ID conditions, and between the two shift conditions and the Maintain-Rule trials. Consistent with the previous literature, these data indicated that ED- and ID-Shifts require different levels of neural resources. A secondary goal of this experiment was to use the excellent temporal resolution of ERPs to examine the neural correlates of various other aspects of the performance of a set-shift task, including differences between correct shifts and the commission of errors, and the differences between the reception of correct and error feedback. Comparisons were made between ERP averages to correct ED-Shift trials and ED-Error trials, and to feedback following a correct ED-Shift compared to feedback following an error. As expected, ERP differences were found between correct trials and error trials, and between the ERP correlates of receiving different types of feedback. Overall, these data further indicate the utility of using ERP methodology to study various aspects of complex neuropsychological paradigms.

The BOLD response during Stroop task-like inhibition paradigms: Effects of task difficulty and task-relevant modality

Previous studies of the Stroop task propose two key mediators: the prefrontal and cingulate cortices but hints exist of functional specialization within these regions. This study aimed to examine the effect of task modality upon the prefrontal and cingulate response by examining the response to colour, number, and shape Stroop tasks whilst BOLD fMRI images were acquired on a Siemens 3T MRI scanner. Behavioural analyses indicated facilitation and interference effects and a noticeable effect of task difficulty. Some modular effects of modality were observed in the prefrontal cortex that survived exclusion of task difficulty related activations. No effect of task-relevant information was observed in the anterior cingulate. Future comparisons of the mediation of selective attention need to consider the effects of task context and task difficulty.

From genes to brain oscillations: Is the visual pathway the epigenetic clue to schizophrenia?

Molecular data and gene expression data and recently mitochondrial genes and possible epigenetic regulation by non-coding genes is revolutionizing our views on schizophrenia. Genes and epigenetic mechanisms are triggered by cell-cell interaction and by external stimuli. A number of recent clinical and molecular observations indicate that epigenetic factors may be operational in the origin of the illness. Based on the molecular insights, gene expression profiles and epigenetic regulation of gene, we went back to the neurophysiology (brain oscillations) and found a putative role of the visual experiences (i.e. visual stimuli) as epigenetic factor. The functional evidences provided here, establish a direct link between the striate and extrastriate unimodal visual cortex and the neurobiology of the schizophrenia. This result support the hypothesis that 'visual experience' has a potential role as epigenetic factor and contribute to trigger and/or to maintain the progression of the schizophrenia. In this case, candidate genes sensible for the visual 'insult' may be located within the visual cortex including associative areas, while the integrity of the visual pathway before reaching the primary visual cortex is preserved. The same effect can be perceived if target genes are localised within the visual pathway, which actually, is more sensitive for 'insult' during the early life than the cortex per se. If this process affects gene expression at these sites a stably sensory specific 'insult', i.e. distorted visual information, is entering the visual system and expanded to fronto-temporo-parietal multimodal areas even from early maturation periods. The difference in the timing of postnatal neuroanatomical events between such areas and the primary visual cortex in humans (with the formers reaching the same development landmarks later in life than the latter) is 'optimal' to establish an abnormal 'cell- communication' mediated by the visual system that may further interfere with the local physiology. In this context the strategy to search target genes need to be rearrangement and redirected to visual-related genes. Otherwise, psychophysics studies combining functional neuroimage, and electrophysiology are strongly recommended, for the search of epigenetic clues that will allow to carrier gene association studies in schizophrenia.

The effect of social content on deductive reasoning: an fMRI study

Psychological studies of deductive reasoning have shown that subjects' performance is affected significantly by the content of the presented stimuli. Specifically, subjects find it easier to reason about contexts and situations with a social content. In the present study, the effect of content on brain activation was investigated with functional magnetic resonance imaging (fMRI) while subjects were solving two versions of the Wason selection task, which previous behavioral studies have shown to elicit a significant content effect. One version described an arbitrary relation between two actions (Descriptive: "If someone does ..., then he does ..."), whereas the other described an exchange of goods between two persons (Social-Exchange: "If you give me ..., then I give you ..."). Random-effect statistical analyses showed that compared to baseline, both tasks activated frontal medial cortex and left dorsolateral frontal and parietal regions, confirming the major role of the left hemisphere in deductive reasoning. In addition, although the two reasoning conditions were identical in logical form, the social-exchange task was also associated with right frontal and parietal activations, mirroring the left-sided activations common to both reasoning tasks. These results suggest that the recruitment of the right hemisphere is dependent on the content of the stimuli presented.

Frontal lobe activation during object alternation acquisition

Object alternation (OA) tasks are increasingly used as probes of ventral prefrontal functioning in humans. In the most common variant of the OA task, subjects must deduce the task rule through trial-and-error learning. To examine the neural correlates of OA acquisition, the authors measured regional cerebral blood flow with positron emission tomography while subjects acquired an OA task, performed a sensorimotor control condition, or performed already learned and practiced OA. As expected, activations emerged in the ventral prefrontal cortex. However, activation of the presupplemental motor area was more closely associated with successful task performance. The authors suggest that areas beyond the ventral prefrontal cortex are critically involved in OA acquisition.

Adaptive modulation of color salience contingent upon global form coding and task relevance

Extensive research on local color aftereffects has revealed perceptual consequences of opponent color coding in the retina and the LGN, and of orientation-and/or spatial-frequency-contingent color coding in early cortical visual areas (e.g., V1 and V2). Here, we report a color aftereffect that depends crucially on global-form-contingent color processing. Brief viewing of colored items (passively viewed, ignored, or attended) reduced the salience of the previewed color in a subsequent task of color-based visual search. This color-salience aftereffect was relatively insensitive to variations (between color preview and search) in local image features, but was substantially affected by changes in global configuration (e.g. the presence or absence of perceptual unitization); the global-form dependence of the aftereffect was also modulated by task demands. The overall results suggest that (1) color salience is adaptively modulated (from fixation to fixation), drawing attention to a new color in visual-search contexts, and (2) these modulations seem to be mediated by global-form-and-color-selective neural processing in mid to late stages of the ventral visual pathway (e.g., V4 and IT), in combination with task-dependent feedback from higher cortical areas (e.g., prefrontal cortex).

The cerebral correlates of different types of perseveration in the Wisconsin Card Sorting Test

OBJECTIVES

To explore the neural substrates corresponding to the perseverative errors in the Wisconsin Card Sorting Test (WCST).

METHODS

The study examined the correlations between the WCST performances and the SPECT measurements of regional cerebral blood flow (rCBF) in subjects with neurodegenerative dementia. Negative non-linear correlations between the rCBF and the two different types of the perseverative errors ("stuck-in-set" and "recurrent" perseverative errors) were calculated on a voxel basis and volume-of-interest basis in the mixed groups of 72 elderly and dementia patients.

RESULTS

The stuck-in-set perseverative error was associated with the reduced rCBF in the rostrodorsal prefrontal cortex, whereas the recurrent perseverative error was related to the left parietal activity but not to the prefrontal activity.

CONCLUSIONS

These findings augment evidence that the rostrodorsal prefrontal cortex crucially mediates attentional set shifting, and suggest that the stuck-in-set perseverative errors would be a true pathognomonic sign of frontal dysfunction. Moreover, this study shows that the recurrent perseverative errors may not be associated closely with the prefrontal function, suggesting that this error and the stuck-in-set error should be differentially estimated in the WCST.

Switching between spatial stimulus-response mappings: a developmental study of cognitive flexibility

Four different age groups (8-9-year-olds, 11-12-year-olds, 13-15-year-olds and young adults) performed a spatial rule-switch task in which the sorting rule had to be detected on the basis of feedback or on the basis of switch cues. Performance errors were examined on the basis of a recently introduced method of error scoring for the Wisconsin Card Sorting Task (WCST; Barcelo & Knight, 2002). This method allowed us to differentiate between errors due to failure-to-maintain-set (distraction errors) and errors due to failure-to-switch-set (perseverative errors). The anticipated age differences in performance errors were most pronounced for perseverative errors between 8-9 years and 11-12 years, but for distraction errors adult levels were not reached until 13-15 years. These findings were interpreted to support the notion that set switching and set maintenance follow distinct developmental trajectories.

Age-related changes in the efficiency of cognitive processing across the life span

The global-speed and the specific-gain/loss hypotheses have been dominant theoretical frameworks in the recent literature on cognitive development and aging. Few attempts have been made to explicitly assess the predictive power of the two frameworks against each other. We evaluated the extent to which age changes in performance in executive function tasks (involving response selection, response suppression, working memory, and adaptive control) depend on age-related changes in global information-processing speed. Our sample consisted of children, adolescents, adults and seniors. Analysis of covariance and structural equation modeling revealed a mixed pattern of results. Controlling for global speed removed the child vs. adult differences in the speed of responding on the executive function tasks but the senior vs. adult differences remained. This mixed pattern of findings was interpreted to suggest that the effects of advancing age on the speed of responding are mediated by a global mechanism during childhood but during senescence the efficiency of executive functioning seems particularly vulnerable to the effects of age.

Neural correlates of switching set as measured in fast, event-related functional magnetic resonance imaging

Attentional switching has shown to involve several prefrontal and parietal brain regions. Most cognitive paradigms used to measure cognitive switching such as the Wisconsin Card Sorting Task (WCST) involve additional cognitive processes besides switching, in particular working memory (WM). It is, therefore, questionable whether prefrontal brain regions activated in these conditions, especially dorsolateral prefrontal cortex (DLPFC), are involved in cognitive switching per se, or are related to WM components involved in switching tasks. Functional magnetic resonance imaging (fMRI) was used to examine neural correlates of pure switching using a paradigm purposely designed to minimize WM functions. The switching paradigm required subjects to switch unpredictably between two spatial dimensions, clearly indicated throughout the task before each trial. Fast, event-related fMRI was used to compare neural activation associated with switch trials to that related to repeat trials in 20 healthy, right-handed, adult males. A large cluster of activation was observed in the right hemisphere, extending from inferior prefrontal and pre- and postcentral gyri to superior temporal and inferior parietal cortices. A smaller and more caudal cluster of homologous activation in the left hemisphere was accompanied by activation of left dorsolateral prefrontal cortex (DLPFC). We conclude that left DLPFC activation is involved directly in cognitive switching, in conjunction with parietal and temporal brain regions. Pre- and postcentral gyrus activation may be related to motor components of switching set.

A review of the cognitive and behavioral sequelae of Parkinson's disease: relationship to frontostriatal circuitry

BACKGROUND

Parkinson's disease is a neurodegenerative hypokinetic movement disorder presenting with subcortical pathology and characterized by motor deficits. However, as is frequently reported in the literature, patients with Parkinson's disease can also exhibit cognitive and behavioral impairments. These impairments may be attributed to dysfunction of multiple systems associated with the disease process in Parkinson's disease that are not necessarily related to motor symptoms. In recent years, considerable attention has addressed the circuits connecting the frontal cortical regions and the basal ganglia (i.e., frontostriatal circuits) and how they mediate cognition and behavior in humans. It has been suggested that these same circuits are disrupted in Parkinson's disease and may be responsible for the frontal/executive deficits predominantly reported in this patient population.

OBJECTIVE

The current survey of the literature provides a critique and analysis of the neuropsychological profile of Parkinson's disease, including cognitive impairments, behavioral alterations, and emotional processing deficits. A special feature of this paper is to ascertain how frontostriatal circuitry might provide the substrate for the neuropsychological impairments exhibited in Parkinson's disease. In so doing, studies involving nonhuman subjects, neurologically healthy adults, brain-lesioned individuals, and patients with Parkinson's disease are reviewed to provide a novel perspective in conceptualizing and categorizing the cognitive and behavioral sequelae concomitant to specific frontostriatal circuit dysfunction in Parkinson's disease.

CONCLUSIONS

The current review suggests that the neuropsychological profile of Parkinson's disease, which predominantly reflects frontal/executive dysfunction, may be attributed to disruption of the frontostriatal circuitry. The information generated from this review can serve as a guide in the assessment of frontal/executive dysfunction in Parkinson's disease with suggestions for a clinical neuropsychological test battery.

Cardiac concomitants of feedback processing

This study examined the heart rate changes associated with positive and negative performance feedback in a probabilistic learning task derived from Holroyd and Coles (Psychological Review, 109 (2002) 679). In this task, subjects were presented with six stimuli and asked to respond by pressing a left versus right key. Responses were followed by positive or negative feedback. Subjects had to infer the S-R mapping rule on the basis of feedback provided to them. Two stimuli were consistently mapped onto the left versus right key (100% mapping). Two other stimuli were randomly mapped onto the keys (50% mapping) and responses to the two remaining stimuli received always positive or negative feedback (always condition). Negative feedback was associated with heart rate slowing in the 100% condition. Heart rate slowed following both positive and negative feedback in the 50% condition, but only when the previous encounter with the stimulus was followed by alternate feedback. Heart rate did not differentiate between positive and negative feedback in the always condition. The results were interpreted in support of the hypothesis assuming that heart rate slowing is elicited when performance-based expectations are violated.

Human brain regions required for the dividing and switching of attention between two features of a single object

This combined PET and ERP study was designed to identify the brain regions activated in switching and divided attention between different features of a single object using matched sensory stimuli and motor response. The ERP data have previously been reported in this journal [64]. We now present the corresponding PET data. We identified partially overlapping neural networks with paradigms requiring the switching or dividing of attention between the elements of complex visual stimuli. Regions of activation were found in the prefrontal and temporal cortices and cerebellum. Each task resulted in different prefrontal cortical regions of activation lending support to the functional subspecialisation of the prefrontal and temporal cortices being based on the cognitive operations required rather than the stimuli themselves.

Induced oscillations and the distributed cortical sources during the Wisconsin card sorting test performance in schizophrenic patients: new clues to neural connectivity

Prefrontal dysfunction has been associated with schizophrenia. Activation during Wisconsin card sorting test (WCST) is a common approach used in functional neuroimaging to address this failure. Equally, current knowledge states that oscillations are basic forms of cells-assembly communications during mental activity. Promising results were revealed in a previous study assessing healthy subjects, WCST and oscillations. However, those previous studies failed to meet the functional integration of the network during the WCST in schizophrenics, based on the induced oscillations and their distributed cortical sources. In this research, we utilized the brain electrical tomography (variable-resolution brain electromagnetic tomography) technique to accomplish this goal. Task specific delta, theta, alpha and beta-2 oscillations were induced and simultaneously synchronized over large extensions of cortex, encompassing prefrontal, temporal and posterior regions as in healthy subjects. Every frequency had a well-defined network involving a variable number of areas and sharing some of them. Oscillations at 11.5, 5.0 and 30 Hz seem to reflect an abnormal increase or decrease, being located at supplementary motor area (SMA), left occipitotemporal region (OT), and right frontotemporal subregions (RFT), respectively. Three cortical areas appeared to be critical, that may lead to difficulties either in coordinating/sequencing the input/output of the prefrontal networks-SMA, and retention of information in memory-RFT, both preceded or paralleled by a deficient visual information processing-OT.

The role of prefrontal cortex in working-memory capacity, executive attention, and general fluid intelligence: an individual-differences perspective

We provide an "executive-attention" framework for organizing the cognitive neuroscience research on the constructs of working-memory capacity (WMC), general fluid intelligence, and prefrontal cortex (PFC) function. Rather than provide a novel theory of PFC function, we synthesize a wealth of single-cell, brain-imaging, and neuropsychological research through the lens of our theory of normal individual differences in WMC and attention control (Engle, Kane, & Tuholski, 1999; Engle, Tuholski, Laughlin, & Conway, 1999). Our critical review confirms the prevalent view that dorsolateral PFC circuitry is critical to executive-attention functions. Moreover, although the dorsolateral PFC is but one critical structure in a network of anterior and posterior "attention control" areas, it does have a unique executive-attention role in actively maintaining access to stimulus representations and goals in interference-rich contexts. Our review suggests the utility of an executive-attention framework for guiding future research on both PFC function and cognitive control.

Think differently: a brain orienting response to task novelty

Cognitive flexibility hinges on a readiness to direct attention to novel events, and on an ability to change one's mental set to find new solutions for old problems. Human event-related potential (ERP) studies have described a brain 'orienting' response to discrete novel events, marked by a frontally distributed positive potential peaking 300-400 ms post-stimulus (P3a). This brain potential has been typically related to bottom-up processing of novel non-targets under a fixed task-set (i.e., press a button to coloured targets), but had never been related to top-down attention control in dual-task paradigms. In this study, 27 subjects had their ERPs measured while they performed a version of the Wisconsin card sorting test (WCST), a dual-task paradigm where the same feedback cue signalled unpredictable shifts to a new task set (i.e., from 'sort by colour' to 'sort by shape'). Feedback cues that directed a shift in the subject's mental set to a new task-set elicited frontally distributed P3a activity, thus suggesting a role of the P3a response system in task-set shifting. Feedback cues also evoked a longer latency positive potential (350-600 ms; P3b), that was larger the more task rules were held in memory. In line with current models of prefrontal function in the executive control of attention, this P3a/P3b response system appears to reflect the co-ordinated action of prefrontal and posterior association cortices during the switching and updating of task sets in working memory.

Perseverative behavior and adaptive control in older adults: performance monitoring, rule induction, and set shifting

Older adults, like patients with dorsolateral frontal lobe lesions, have been shown to be progressively susceptible to errors of perseveration in the Wisconsin Card Sorting Test (WCST). This deficit may result from several types of endogenous adaptive control abilities. First, to enable behavioral modifications in response to sudden changes in task demands, one has to consider and evaluate the possible alternative categorization rules and select one for further testing (rule induction). Second, to perform the required shift appropriately, one should suppress the no-longer relevant task set and replace it by an appropriate new one (set shifting). Third, however, proper application of rule-induction and set-shifting abilities requires the ability to monitor and interpret task cues and feedback signals appropriately to guide behavior and to recognize the need to apply rule-shift operations (performance monitoring). To explore the extent to which these different endogenous adaptive control abilities are differentially sensitive to the effect of aging, young and older adults were tested in two experiments using WCST-like tasks. From the finding that older adults were not able to capitalize on explicit shift cues (either nonspecific or specific) the inference can be drawn that basic set-shifting abilities, rather than rule-induction or performance-monitoring abilities, were the primary factor responsible for the increased tendency to perseverate as adults grow into senescence.

Wisconsin Card Sorting Test synchronizes the prefrontal, temporal and posterior association cortex in different frequency ranges and extensions

Current findings show some brain regions consistently related to performance of the Wisconsin Card Sorting Test (WCST). An increase of local cerebral blood flow or metabolic demands has been detected in those regions. Functional integration of the neuronal circuits that subserve the task performance, based upon the identification of the oscillations and their distributed cerebral sources, has not been accomplished previously. The event-related tonic oscillations within a period of 2,000 msec after the stimulus onset and the probable neural substrate were evaluated in healthy volunteers by variable-resolution brain electrical tomography (VARETA). The WCST induced a significant increase of delta, theta, beta-2, and gamma oscillations, but decrease of alpha. Areas such as the frontal subregions, temporal, cingulate, parahippocampal, parietal, occipitotemporal cortex, and occipital poles showed modified activity during the task, with EEG spectral band selectivity as well as some overlapping among them. Frontal and temporal regions generated the delta/theta oscillations. Additionally, the occipitotemporal and parietal regions were the source of the delta activity, lacking theta activation. The parietal region also showed tonic alpha, beta-2 and gamma changes. These data imply that different processes have been simultaneously mediated during task performance. Relationships among the individual bands, the neural substrata and the specific cognitive process that support the task were established. The selectively distributed delta, theta, alpha, beta-2 and gamma oscillations reflect communication networks through variable populations of neurons, with functional relations to the working memory functions and the information processing that subserve the WCST performance.

A code for behavioral inhibition on the basis of color, but not motion, in ventrolateral prefrontal cortex of macaque monkey

To examine the neural mechanism for behavioral inhibition, we recorded single-cell activity in macaque ventrolateral prefrontal cortex, which is known to receive visual information directly from the inferotemporal cortex. In response to a moving random pattern of colored dots, monkeys had to make a go or no-go response. In the color condition, green indicated go, whereas red indicated no-go, regardless of the motion direction; in the motion condition, upward indicated go, whereas downward indicated no-go, regardless of the color. Approximately one-half of the visual cells were go/no-go differential. A majority of these cells (64/73) showed differential activity only in the color condition; they responded nondifferentially in the motion condition, although the same set of stimuli was used. We classified these cells as "go type" (n = 41) and "no-go type" (n = 23) depending on the color for which they showed a stronger response. Interestingly, in both types of cells, the differential effects were observed only for the no-go-indicating color. Compared with the nondifferential responses in the motion condition, go-type cells in the color condition showed weaker responses to the no-go-indicating color, whereas their responses to the go-indicating color were similar; in contrast, no-go type cells showed stronger responses to the no-go-indicating color, whereas their responses to the go-indicating color were similar. Both types of cells did not show any activity change during the actual execution of the go or no-go response. These results suggest that neurons in ventrolateral prefrontal cortex contribute to stimulus-response association in complex task situations by inhibiting behavioral responses on the basis of visual information from the ventral stream.

Does the Wisconsin Card Sorting Test measure prefontral function?

This review describes a research program aimed at evaluating the validity and specificity of the Wisconsin Card Sorting Test (WCST), one of the most widely used tests of prefrontal function in clinical and experimental neuropsychology. In spite of its extensive use, voices of caution have arisen against the use of WCST scores as direct markers of prefrontal damage or dysfunction. Adopting a cognitive neuroscience approach, the present research program integrates behavioral, physiological, and anatomical information to investigate the cognitive and neural mechanisms behind WCST performance. The results show that WCST performance evokes conspicuous physiological changes over frontal as well as posterior brain regions. Moreover, WCST scores confound very heterogeneous cognitive and neural processes. This confounding effect may have led many authors to overlook the relative importance of certain dysfunctional states such as those indexed by random errors. These findings strongly suggest that WCST scores cannot be regarded as valid nor specific markers of prefrontal lobe function. However, they do provide some relevant clues to update our current knowledge about prefrontal function. In the long run, the integrative approach of cognitive neuroscience may help us design and develop more valid and sensitive tools for neuropsychological assessment.

Mapping motor inhibition: conjunctive brain activations across different versions of go/no-go and stop tasks

Conjunction analysis methods were used in functional magnetic resonance imaging to investigate brain regions commonly activated in subjects performing different versions of go/no-go and stop tasks, differing in probability of inhibitory signals and/or contrast conditions. Generic brain activation maps highlighted brain regions commonly activated in (a) two different go/no-go task versions, (b) three different stop task versions, and (c) all 5 inhibition task versions. Comparison between the generic activation maps of stop and go/no-go task versions revealed inhibitory mechanisms specific to go/no-go or stop task performance in 15 healthy, right-handed, male adults. In the go/no-go task a motor response had to be selectively executed or inhibited in either 50% or 30% of trials. In the stop task, the motor response to a go-stimulus had to be retracted on either 50 or 30% of trials, indicated by a stop signal, shortly (250 ms) following the go-stimulus. The shared "inhibitory" neurocognitive network by all inhibition tasks comprised mesial, medial, and inferior frontal and parietal cortices. Generic activation of the go/no-go task versions identified bilateral, but more predominantly left hemispheric mesial, medial, and inferior frontal and parietal cortices. Common activation to all stop task versions was in predominantly right hemispheric anterior cingulate, supplementary motor area, inferior prefrontal, and parietal cortices. On direct comparison between generic stop and go/no-go activation maps increased BOLD signal was observed in left hemispheric dorsolateral prefrontal, medial, and parietal cortices during the go/no-go task, presumably reflecting a left frontoparietal specialization for response selection.

Prefrontal, parietal, and temporal cortex networks underlie decision-making in the presence of uncertainty

Decision-making in the presence of uncertainty, i.e., selecting a sequence of responses in an uncertain environment according to a self-generated plan of action, is a complex activity that involves both cognitive and noncognitive processes. Using functional magnetic resonance imaging, the neural substrates of decision-making in the presence of uncertainty are examined. Normal control subjects show a significant activation of a frontoparietal and limbic neural system during a two-choice prediction task relative to a two-choice response task. The most prevalent response strategy during the two-choice prediction task was "win-stay/lose-shift," where subjects will repeat the previous response if it successfully predicted the stimulus and switch to the alternative response otherwise. Increased frequency of responses that are consistent with this strategy is associated with activation in the superior temporal gyrus. In comparison, increased frequency of response inconsistent with win-stay/lose-shift is associated with parietal cortex activation. These results support the hypothesis that subjects use a frontoparietal neural system to establish a contingency based decision-making strategy even in the presence of random reinforcement.

Dissociable mechanisms of attentional control within the human prefrontal cortex

Neuropsychological tests that require shifting an attentional set, such as the Wisconsin Card Sorting Test, are sensitive to frontal lobe damage. Although little information is available for humans, an animal experiment suggested that different regions of the prefrontal cortex may contribute to set shifting behavior at different levels of processing. Behavioral studies also suggest that set shifting trials are more time consuming than non-set shifting trials (i.e. switch cost) and that this may be underpinned by differences at the neural level. We determined whether there were differential neural responses associated with two different levels of shifting behavior, that of reversal of stimulus-response associations within a perceptual dimension or that of shifting an attentional set between different perceptual dimensions. Neural activity in the antero-dorsal prefrontal cortex increased only in attentional set shifting, in which switch costs were significant. Activity in the postero-ventral prefrontal cortex increased not only in set shifting but also in reversing stimulus-response associations, in which switch costs were absent. We conclude that these distinct regions in the human prefrontal cortex provide different levels of attention control in response selection. Thus, the antero-dorsal prefrontal cortex may be critical for higher order control of attention, i.e. attentional set shifting, whereas the postero-ventral area may be related to a lower level of shift, i.e. reorganizing stimulus-response associations.

A comparison of frontoparietal fMRI activation during anti-saccades and anti-pointing

An anti-saccade, which is a saccade directed toward a mirror-symmetrical position in the opposite visual field relative to the visual stimulus, involves at least three separate operations: covert orienting, response suppression, and coordinate transformation. The distinction between pro- and anti-saccades can also be applied to pointing. We used fMRI to compare patterns of brain activation during pro- and anti-movements, to determine whether or not additional areas become active during the production of anti-movements. In parietal cortex, an inferior network was active during both saccades and pointing that included three foci along the intraparietal sulcus: 1) a posterior superior parietal area (pSPR), more active during the anti-tasks; 2) a middle inferior parietal area (mIPR), active only during the anti-tasks; and 3) an anterior inferior parietal area (aIPR), equally active for pro- and anti-movement. A superior parietal network was active during pointing but not saccades and included the following: 1) a medial region, active during anti- but not pro-pointing (mSPR); 2) an anterior and medial region, more active during pro-pointing (aSPR); and 3) an anterior and lateral region, equally active for pro- and anti-pointing (lSPR). In frontal cortex, areas selectively active during anti-movement were adjacent and anterior to areas that were active during both the anti- and pro-tasks, i.e., were anterior to the frontal eye field and the supplementary motor area. All saccade areas were also active during pointing. In contrast, foci in the dorsal premotor area, the anterior superior frontal region, and anterior cingulate were active during pointing but not saccades. In summary, pointing with central gaze activates a frontoparietal network that includes the saccade network. The operations required for the production of anti-movements recruited additional frontoparietal areas.

Cortical activity related to accuracy of letter recognition

Previous imaging and neurophysiological studies have suggested that the posterior inferior temporal region participates in tasks requiring the recognition of objects, including faces, words, and letters; however, the relationship between accuracy of recognition and activity in that region has not been systematically investigated. In this study, positron emission tomography was used to estimate glucose metabolism in 60 normal adults performing a computer-generated letter-recognition task. Both a region of interest and a voxel-based method of analysis, with subject state and trait variables statistically controlled, found task accuracy to be: (1) negatively related to metabolism in the left ventrolateral inferior temporal occipital cortex (Brodmann's area 37, or ventrolateral BA 37) and (2) positively related to metabolism in a region of the right ventrolateral frontal cortex (Brodmann's areas 47 and 11, or right BA 47/11). Left ventrolateral BA 37 was significantly related both to hits and to false alarms, whereas the right BA 47/11 finding was related only to false alarms. The results were taken as supporting an automaticity mechanism for left ventrolateral BA 37, whereby task accuracy was associated with automatic letter recognition and in turn to reduced metabolism in this extrastriate area. The right BA 47/11 finding was interpreted as reflecting a separate component of task accuracy, associated with selectivity of attention broadly and with inhibition of erroneous responding in particular. The findings are interpreted as supporting the need for control of variance due to subject and task variables, not only in correlational but also in subtraction designs.

Transient neural activity in the medial superior frontal gyrus and precuneus time locked with attention shift between object features

To investigate the contribution of the superior frontal gyrus and precuneus to the cognitive process of attention set shift, we examined the correlation between change in neural activity in these areas and the timing of attention set shift using event-related functional magnetic resonance imaging. Seven subjects underwent a card-sorting task in which they matched a test card to one of two target cards according to color or shape. The subjects had to determine the correct category based only on feedback and shift the sorting principle when the feedback changed from "correct" to "incorrect." Transient increase of neural activity time locked with attention shift phases was detected in the medial superior frontal gyrus (the rostral part of the supplementary motor area) and precuneus. During the control task, in which the feedback and the motor responses were preserved without any attention shift, this type of change in neural activity was not observed. Our findings indicate that increase in neural activity in these brain areas may be closely related to attention set shift between object features and suggest that these areas may play a role in the shifting of cognitive sets.