Impaired extra-dimensional shift performance in medicated and unmedicated Parkinson's disease: evidence for a specific attentional dysfunction

Behavioral persistence deficit in Parkinson's disease patients

The present study was performed to examine the degree to which decreased task persistence may contribute to deficits in the ability of Parkinson's disease (PD) patients to perform a problem solving task. Patients with mild/moderate PD performed a computerized Tower of Hanoi task in which they planned and verbalized moves to solve the puzzle but did not need to produce a limb motor response. All patients were tested at least 14 h off medication. As expected from previous studies of planning abilities in PD, patients had significant problems performing this task and accuracy decreased specifically when patients were presented with the most difficult puzzles in the sequence. PD patients solved fewer of the most difficult puzzles than did control subjects, but also made significantly fewer attempts to solve those puzzles than controls. These results suggest that PD patients not only have planning and problem solving deficits as have been documented previously, but that at least part of this and perhaps other cognitive performance problems may result from difficulty in maintaining adequate mental effort to successfully complete difficult tasks.

Forebrain connectivity of the prefrontal cortex in the marmoset monkey (Callithrix jacchus): an anterograde and retrograde tract-tracing study

The cortical and subcortical forebrain connections of the marmoset prefrontal cortex (PFC) were examined by injecting the retrograde tracer, choleratoxin, and the anterograde tracer, biotin dextran amine, into four sites within the PFC. Two of the sites, the lateral and orbital regions, had previously been shown to provide functionally dissociable contributions to distinct forms of behavioral flexibility, attentional set-shifting and discrimination reversal learning, respectively. The dysgranular and agranular regions lying on the orbital and medial surfaces of the frontal lobes were most closely connected with limbic structures including cingulate cortex, amygdala, parahippocampal cortex, subiculum, hippocampus, hypothalamus, medial caudate nucleus, and nucleus accumbens as well as the magnocellular division of the mediodorsal nucleus of the thalamus and midline thalamic nuclei, consistent with findings in the rhesus monkey. In contrast, the granular region on the dorsal surface closely resembled area 8Ad in macaques and had connections restricted to posterior parietal cortex primarily associated with visuospatial functions. However, it also had connections with limbic cortex, including retrosplenial and caudal cingulate cortex as well as auditory processing regions in the superior temporal cortex. The granular region on the lateral convexity had the most extensive connections. Based on its architectonics and functionality, it resembled areas 12/45 in macaques. It had connections with high-order visual processing regions in the inferotemporal cortex and posterior parietal cortex, higher-order auditory and polymodal processing regions in the superior temporal cortex. In addition it had extensive connections with limbic regions including the amygdala, parahippocampal cortex, cingulate, and retrosplenial cortex.

Dopamine asymmetry interacts with medication to affect cognition in Parkinson's disease

Contradictory evidence exists regarding the nature and degree of impaired cognitive flexibility in PD. Dopaminergic medication may be expected to ameliorate such cognitive deficits, yet both medicated and unmedicated patients have been reported to perform more poorly than control subjects on tasks of cognitive flexibility, suggesting that such deficits may also be affected by other disease-related variables. The present study examined whether asymmetric dopamine deficiency (revealed by unilateral symptom onset) is related to the performance of spontaneous and reactive flexibility in PD, and the possible interaction of dopaminergic medication with such asymmetry. Thirty-five PD patients with mild motor symptoms and unilateral onset of PD (left-onset=14; right-onset=21) performed the Alternate Uses (AU) and intradimensional/extradimensional shift (IED) tasks. Interaction between side of onset and medication was observed for the number of errors in the AU task and number of reversal errors in the IED task. Significantly more AU errors were made by medicated patients with left-onset, as compared to all other participants. Conversely, medicated patients with right-onset made the most reversal errors. These results suggest that relatively early in the disease process when dopamine deficit in the less-affected hemisphere is mild, optimal dopaminergic medication (with respect to motor function) may involve over-medication of the less-affected hemisphere. Thus, AU errors may be the consequence of hyperdopaminergic state leading to impaired functioning of the left hemisphere, whereas increased reversal errors in right-onset PD patients receiving dopaminergic medication is related to impaired dopamine function in the right hemisphere.

Multiple dopamine functions at different time courses

Many lesion studies report an amazing variety of deficits in behavioral functions that cannot possibly be encoded in great detail by the relatively small number of midbrain dopamine neurons. Although hoping to unravel a single dopamine function underlying these phenomena, electrophysiological and neurochemical studies still give a confusing, mutually exclusive, and partly contradictory account of dopamine's role in behavior. However, the speed of observed phasic dopamine changes varies several thousand fold, which offers a means to differentiate the behavioral relationships according to their time courses. Thus dopamine is involved in mediating the reactivity of the organism to the environment at different time scales, from fast impulse responses related to reward via slower changes with uncertainty, punishment, and possibly movement to the tonic enabling of postsynaptic motor, cognitive, and motivational systems deficient in Parkinson's disease.

Intra-dimensional/extra-dimensional set-shifting performance in schizophrenia: impact of distractors

BACKGROUND

We sought to determine if a representative group of young chronic patients with schizophrenia would demonstrate selective impairments in set shifting processes of the CANTAB Intra-dimensional/extra-dimensional (IDED) task. We predicted that patients would have prominent difficulties with Compound Discrimination (C_D) (stage of the task in which irrelevant stimuli are introduced) and Extra-Dimensional Shifting (EDS) (stage of the task in which a new stimulus dimension must be attended) on the basis of the results of cortical hypodopaminergic states in subhuman primates (for C_D) and effects of dorsolateral prefrontal cortical lesions on set shifting and prior results in schizophrenia (for EDS).

METHODS

We administered the IDED to 36 patients and 26 healthy controls. Additionally, we administered the Wisconsin Card Sorting Test (WCST), another test of set shifting, and a Continuous Performance Test (CPT) type task of attention to patients with schizophrenia in order to investigate which cognitive components accounted for performance difficulties at different stages of the IDED task.

RESULTS

Patients had selective difficulties on C_D and EDS stages of the task. In schizophrenic patients early stages of the task involving the introduction and establishment of attentional set were correlated to CPT performance, while later set shifting stages were correlated with WCST categories attained.

CONCLUSION

We found evidence that patients with schizophrenia were susceptible to introduction of unreinforced irrelevant stimuli at the C_D stage, such that the previously rewarded target stimuli no longer held hegemony as a representation. This type of processing failure may reflect difficulties in stabilizing a representation and is consistent with effects of prefrontal hypodopaminergia in primates. Secondly, "survivors" of this stage experienced marked difficulties on EDS-stage, suggestive of classic prefrontal failures.

The Human Striatum is Necessary for Responding to Changes in Stimulus Relevance

Various lines of evidence suggest that the striatum is implicated in cognitive flexibility. The neuropsychological evidence has, for the most part, been based on research with patients with Parkinson's disease, which is accompanied by chemical disruption of both the striatum and the prefrontal cortex. The present study examined this issue by testing patients with focal lesions of the striatum on a task measuring two forms of cognitive switching. Patients with striatal, but not frontal lobe lesions, were impaired in switching between concrete sensory stimuli. By contrast, both patient groups were unimpaired when switching between abstract task rules relative to baseline nonswitch trials. These results reveal a dissociation between two distinct forms of cognitive f lexibility, providing converging evidence for a role of the striatum in f lexible control functions associated with the selection of behaviorally relevant stimuli.

Effects of nicotinic therapies on attention and executive functions in chronic low-dose MPTP-treated monkeys

Chronic administration of low doses of the neurotoxin MPTP to nonhuman primates induces cognitive deficits similar to those seen in early Parkinson's disease (PD) patients, without the confounding effect of significant motor impairment. The present study assessed the extent to which specific attentional and central executive deficits in chronic low dose (CLD) MPTP-treated monkeys could be modified by nicotinic therapies. Four adult male rhesus monkeys were trained to perform attention and executive function tasks and were then administered low doses of MPTP (dose range: 0.025-0.1 mg/kg, i.v.) over 98-158 days until stable cognitive deficits appeared. Results showed that both nicotine and the alpha4beta4 subtype-selective nAChR agonist SIB-1553A could improve certain aspects of attentional and central executive functioning in this model of early Parkinsonism. Nicotine failed to improve performance of CLD-MPTP-treated animals on an attention set-shifting task while SIB-1553A significantly improved at least some aspects of performance, suggesting that the compound increased the animals' ability to maintain a previously formed response set and restored cognitive flexibility. Both nicotine and SIB-1553A caused a dose-dependent enhancement of performance on the focused attention (cued reaction time) task, decreasing reaction times on both cued and noncued trials. Nicotine caused a significant reduction in reaction times but did not alter the error profile on an impulse (motor readiness) task. SIB-1553A reduced reaction times but caused an increase in bar release (i.e. impulsivity) errors. These data suggest that nicotinic drugs may have therapeutic potential for treating cognitive dysfunction in PD.

The role of learned irrelevance in attentional set-shifting impairments in Parkinson's disease

In this study, the cognitive and neurochemical factors underlying learned irrelevance, one of the mechanisms thought to be responsible for attentional set-shifting deficits in Parkinson's disease (PD), were investigated. In a visual discrimination learning task, the extent to which a target dimension was irrelevant prior to an extra-dimensional shift was varied. Twenty patients with PD and 22 healthy participants performed the task twice, with patients tested on and off L-dopa. The patients made more errors than control participants in the condition in which the target dimension was completely irrelevant prior to the extradimensional shift, but not when it was partially reinforced. Moreover, L-dopa had no effect on the patients' task performance, despite improving their working memory. These results confirm that learned irrelevance is a significant factor in accounting for attentional set-shifting deficits in patients with PD, although unlike other executive impairments in this group, the phenomenon appears to be unrelated to their central dopaminergic deficit.

Impaired self-initiated task preparation during task switching in Parkinson's disease

Patients with Parkinson's disease (PD) typically show reduced performance in clinical tests involving cognitive control processes, presumably due to reduced availability of dopamine in striatofrontal neuronal circuits. Although task switching paradigms are considered as an ideal experimental measure of cognitive control, previous studies on task switching in PD have yielded ambiguous results, indicating that performance deficits depend on the specific task requirements. Among these, the aspect of self-initiated as opposed to externally triggered task preparation seems to play an important role, as evidenced by recent research. To address this topic, the present study investigated PD patients and age-matched controls (n=16) with a sequential switching task in which the upcoming task was predicted by two different types of cues. Firstly, every task was predicted by an external visual cue of varying utility (long versus short precuing interval). Additionally, the tasks were predictable on the basis of a fixed task sequence (AABB), which placed relatively higher demands on self-initiated task preparation. After considerable practice, the sequence was changed to random. Increased reaction times following sequence removal indicated prior use of the sequence in both groups. However, in contrast to healthy age-matched controls, PD patients did not learn to use the predictable task sequence to a greater extent when the utility of the visual task cue was low due to a short precuing interval. This finding is interpreted as evidence for a specific impairment in self-initiated as opposed to externally triggered task preparation.

Functions of frontostriatal systems in cognition: comparative neuropsychopharmacological studies in rats, monkeys and humans

A comparative and integrated account is provided of the evidence that implicates frontostriatal systems in neurodegenerative and neuropsychiatric disorders. Specifically, we have made detailed comparisons of performance following basal ganglia disease such as Parkinson's disease, with other informative groups, including Alzheimer's disease, schizophrenia and attention deficit/hyperactivity disorder and structural damage to the frontal lobes themselves. We have reviewed several behavioural paradigms including spatial attention and set-shifting, working memory and decision-making tasks in which optimal performance requires the operation of several cognitive processes that can be successfully dissociated with suitable precision in experimental animals. The role of ascending neurotransmitter systems are analysed from the perspective of different interactions with the prefrontal cortex. In particular, the role of dopamine in attentional control and spatial working memory is surveyed with reference to its deleterious as well as facilitatory effects. Parallels are identified in humans receiving dopaminergic medication, and with monkeys and rats with frontal dopamine manipulations. The effects of serotonergic manipulations are also contrasted with frontal lobe deficits observed in both humans and animals. The main findings are that certain tests of frontal lobe function are very sensitive to several neurocognitive and neuropsychiatric disorders. However, the nature of some of these deficits often differs qualitatively from those produced by frontal lobe lesions, and animal models have been useful in defining various candidate neural systems thus enabling us to translate basic laboratory science to the clinic, as well as in the reverse direction.

Understanding Obsessive–Compulsive Disorder: Focus on Decision Making

Current approaches to obsessive-compulsive disorder (OCD) have suggested that neurobiological abnormalities play a crucial role in the etiology and course of this psychiatric illness. In particular, a fronto-subcortical circuit, including the orbitofrontal cortex, basal ganglia and thalamus appears to be involved in the expression of OCD symptoms. Neuropsychological studies have also shown that patients with OCD show deficits in cognitive abilities that are strictly linked to the functioning of the frontal lobe and its related fronto-subcortical structures, such as executive functioning deficits and insufficient cognitive-behavioral flexibility. This article focuses on decision making, an executive ability that plays a crucial role in many real-life situations, whereby individuals choose between pursuing strategies of action that involve only immediate reward and others based on long-term reward. Although the role of decision-making deficits in the evolution of OCD requires further research, the collected findings have significant implications for understanding the clinical and behavioral heterogeneity that characterizes individuals with OCD.

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.

Selective extra-dimensional set shifting deficit in a knock-in mouse model of Huntington's disease

People with early-stage Huntington's disease have been found to have a specific deficit in performing an extra-dimensional shift. To date no evidence of this deficit has been identified in transgenic or knock-in rodent models of the disease. The aim of the present paper then, was to test whether homozygous knock-in mice derived from the Hdh(CAG(150)) mouse line were impaired in any of five 2-choice discrimination tasks (simple, compound, compound reversal, intra-dimensional shift and extra-dimensional shift), and whether these mice were impaired at recalling these tasks on the following day. On the extra-dimensional shift task the Hdh(CAG(150)) homozygous mice required a greater number of trials to reach criteria than mice and the percentage of correct choices within the trials was also significantly reduced compared with the animals. For the recall tasks, a deficit for recalling the compound reversal test was found in the Hdh(CAG(150)) homozygous mice for both number of trials required to reach criteria and percentage of correct choices within the trials. Recall for the intra-dimensional shift task was also impaired in these animals when measured by the percentage of correct choices. Our results demonstrate a pronounced deficit in the Hdh(CAG(150)) mice not only on extra-dimensional shift performance in agreement with human studies, but also on recall tasks for both the compound reversal and the intra-dimensional shift tasks.

Focal putamen lesions impair learning in rule-based, but not information-integration categorization tasks

Previous research on the role of the basal ganglia in category learning has focused on patients with Parkinson's and Huntington's disease, neurodegenerative diseases frequently accompanied by additional cortical pathology. The goal of the present study was to extend this work to patients with basal ganglia lesions due to stroke, asking if similar changes in performance would be observed in patients with more focal pathology. Patients with basal ganglia lesions centered in the putamen (6 left side, 1 right side) were tested on rule-based and information-integration visual categorization tasks. In rule-based tasks, it is assumed that participants can learn the category structures through an explicit reasoning process. In information-integration tasks, optimal performance requires the integration of information from two or more stimulus components, and participants are typically unaware of the category rules. Consistent with previous studies involving patients with degenerative disorders of the basal ganglia, the stroke patients were impaired on the rule-based task, and quantitative, model-based analyses indicate that this deficit was due to the inefficient application of decision strategies. In contrast, the patients were unimpaired on the information-integration task. This pattern of results provides converging evidence supporting a role of the basal ganglia and, in particular, the putamen in rule-based category learning.

Are there reliable neuropsychological deficits in obsessive-compulsive disorder?

The aim of this study was to confirm in a large clinical sample that subjects with obsessive-compulsive disorder (OCD) have deficits on certain tasks of executive functioning, non-verbal memory, and/or motor speed. Our ultimate goal was to evaluate whether these deficits contribute to functional impairment and could be the target of a novel treatment intervention. Therefore, in a sample of convenience, the clinical characteristics and neuropsychological performance of adults with OCD and matched healthy controls were evaluated; neuropsychological tasks of executive functioning, non-verbal memory, and motor speed that have shown strong effects in prior studies were used. Primary analyses compared subjects with current OCD only (current-OCD, n=30), subjects with current OCD plus a comorbid disorder (comorbid-OCD, n=15), subjects with a history of OCD (n=15), and matched healthy controls (n=35). Secondary analyses examined whether clinical characteristics (e.g., OCD severity or medication status) were associated with neuropsychological performance. We found no significant overall differences in neuropsychological performance among the four groups. In pairwise comparisons, current-OCD subjects differed significantly from healthy controls only on the Benton Visual Retention Test. OCD severity had little effect and medication status had no effect on neuropsychological performance. In sum, contrary to our expectations, we found few differences in neuropsychological performance between OCD subjects and healthy controls. Whether there are reliable neuropsychological deficits in OCD that can be easily identified in a clinical sample and that contribute to functional impairment remains unclear and requires further study.

Development of cognitive control and executive functions from 4 to 13 years: evidence from manipulations of memory, inhibition, and task switching

Predictions concerning development, interrelations, and possible independence of working memory, inhibition, and cognitive flexibility were tested in 325 participants (roughly 30 per age from 4 to 13 years and young adults; 50% female). All were tested on the same computerized battery, designed to manipulate memory and inhibition independently and together, in steady state (single-task blocks) and during task-switching, and to be appropriate over the lifespan and for neuroimaging (fMRI). This is one of the first studies, in children or adults, to explore: (a) how memory requirements interact with spatial compatibility and (b) spatial incompatibility effects both with stimulus-specific rules (Simon task) and with higher-level, conceptual rules. Even the youngest children could hold information in mind, inhibit a dominant response, and combine those as long as the inhibition required was steady-state and the rules remained constant. Cognitive flexibility (switching between rules), even with memory demands minimized, showed a longer developmental progression, with 13-year-olds still not at adult levels. Effects elicited only in Mixed blocks with adults were found in young children even in single-task blocks; while young children could exercise inhibition in steady state it exacted a cost not seen in adults, who (unlike young children) seemed to re-set their default response when inhibition of the same tendency was required throughout a block. The costs associated with manipulations of inhibition were greater in young children while the costs associated with increasing memory demands were greater in adults. Effects seen only in RT in adults were seen primarily in accuracy in young children. Adults slowed down on difficult trials to preserve accuracy; but the youngest children were impulsive; their RT remained more constant but at an accuracy cost on difficult trials. Contrary to our predictions of independence between memory and inhibition, when matched for difficulty RT correlations between these were as high as 0.8, although accuracy correlations were less than half that. Spatial incompatibility effects and global and local switch costs were evident in children and adults, differing only in size. Other effects (e.g., asymmetric switch costs and the interaction of switching rules and switching response-sites) differed fundamentally over age.

Language, social, and executive functions in high functioning autism: a continuum of performance

This study examined language and executive functions (EF) in high-functioning school-aged individuals with autism and individually matched controls. Relationships between executive, language, and social functioning were also examined. Participants with autism exhibited difficulty on measures of expressive grammar, figurative language, planning, and spatial working memory. A mixed profile of impaired and enhanced abilities was noted in set-shifting. While controls showed the typical increase in errors when shifting sets from an intra-dimensional to an extra-dimensional stimulus, this pattern was not noted in participants with autism. Relationships between EF, language, and social performance were weak to non-existent. Implications for theories of core deficit in autism and dissociable nature of the language and executive impairments in autism are discussed.

Significant cognitive dysfunction in non-delirious patients identified during and persisting following critical illness

OBJECTIVE

Recent studies have shown significant cognitive problems some months after critical illness. However there has been no research examining cognitive function within the intensive care unit (ICU) in non-delirious patients.

DESIGN AND SETTING

A prospective study in an ICU.

PATIENTS AND PARTICIPANTS

Using the Cambridge Neuropsychological Test Automated Battery (CANTAB), 30 long-stay, tracheal-intubated ICU patients were tested. Prior to testing on ICU the Confusion Assessment Measure (CAM-ICU) was administered and only those patients clearly not delirious and off sedation for several days were tested. The CANTAB tests were repeated a week after ICU discharge on the general ward and then again at 2 months. Sixteen patients completed the follow-up.

RESULTS

While on ICU all 30 patients showed significant problems with strategic thinking and problem solving; 20 patients had some problems with memory. The degree of difficulty with problem solving on ICU was correlated with length of ICU stay (p=0.011), age (p=0.036) and length of hospital stay post ICU (p=0.044). Problems with memory in ICU and on the general ward were correlated with admission APACHE II score (p=0.004 and p=0.005 respectively). At the 2-month follow-up 5 of 16 patients (31%) scored below the 25 percentile for memory and 8 of 16 (50%) below the 25 percentile for problem solving (Slater TA, Jones C, Griffiths RD, Wilson S, Benjamin K (2004) Cognitive impairment during and after intensive care: a pilot study. Intensive Care Med 30 [Suppl 1]:S199).

CONCLUSIONS

Difficulties with problem solving and poor memory remained a significant issue for 2 months after ICU discharge.

Visual search deficits in Parkinson's disease are attenuated by bottom-up target salience and top-down information

Patients with Parkinson's disease (PD), a degenerative disorder primarily affecting the nigrostriatal dopamine system, exhibit deficits in selecting task-relevant stimuli in the presence of irrelevant stimuli, such as in visual search tasks. However, results from previous studies suggest that these deficits may vary as a function of whether selection must rely primarily on the "bottom-up" salience of the target relative to background stimuli, or whether "top-down" information about the identity of the target is available to bias selection. In the present study, moderate-to-severe medicated PD patients and age-matched controls were tested on six visual search tasks that systematically varied the relationship between bottom-up target salience (feature search, noisy feature search, conjunction search) and top-down target knowledge (Target Known versus Target Unknown). Comparison of slope and intercepts of the RT x set size function provided information about the efficiency of search and non-search (e.g., decision, response) components, respectively. Patients exhibited higher intercepts than controls as bottom-up target salience decreased, however these deficits were disproportionately larger under Target Unknown compared to Target Known conditions. Slope differences between PD and controls were limited to the Target Unknown Conjunction condition, where patients exhibited a shallower slope in the target absent condition, indicating that they terminated search earlier. These results suggest that under conditions of high background noise, medicated PD patients were primarily impaired in decision and/or response processes downstream from the target search itself, and that the deficit was attenuated when top-down information was available to guide selection of the target signal.

Executive functions in the heterozygous reeler mouse model of schizophrenia

Deficits in working memory and executive functions are now considered among the most reliable endophenotypes for schizophrenia. To determine whether cognitive deficits exist in mouse models of the disease, the authors trained heterozygous reeler (+/rl) mice on a series of visual discriminations similar to those used to test executive abilities in primates. These mice resemble schizophrenia patients in that both have reduced levels of reelin protein and altered gamma aminobutyric acid neurotransmission in the prefrontal cortex. The +/rl mice showed a selective deficit in reversal learning, with a pattern of errors that suggested impaired visual attention rather than a deficiency in perseveration and inhibitory control. These results show that cognitive dysfunction may serve as a useful biomarker in mouse models of neuropsychiatric disease.

Spontaneous blinking behaviour in persistent vegetative and minimally conscious states: Relationships with evolution and outcome

There is evidence that spontaneous blinking correlates with cognitive functions. This arises from the observation that blinking rate (BR) is modulated by arousal levels, basic cognitive processes (e.g., attention, information processing, memory, etc.) and more complex cognitive functions (e.g., reading, speaking, etc.). The aim of this work was to test the role of BR evaluation in the assessment of cognitive network functioning in awake patients with consciousness deficits. Thirteen patients were recruited for the study, and were assessed by the Glasgow coma scale (GCS) and Glasgow outcome scale (GOS) on admittance and discharge, respectively. A level of cognitive functioning scale (LCFS) score was assigned at every change in awareness or at least every 2 weeks. At the same time as the clinical tests, the BR was observed for a 5-min period. Ten healthy subjects, observed throughout three non-consecutive days, formed the control group. The BR underwent a different temporal behaviour in the two diagnostic categories. In the persistent vegetative state (PVS) group it remained stable throughout time and linked with the clinical conditions of the patients; whereas in the non-persistent vegetative state (NPVS) group it decreased over time as the cognitive conditions improved. Moreover, a strong inverse correlation was found between overall BR values and LCFS scores. We have concluded that the blinking behaviour changes manifested in PVS and NPVS patients reflect different evolution phases of a cholinergic-dopaminergic imbalance, and that a reduced BR characterizes the early stages of consciousness recovery.

Discrimination of multidimensional visual stimuli by mice: intra- and extradimensional shifts

A visual discrimination protocol similar to that used with monkeys was adapted to measure attentional set-shifting in mice. An automated touchscreen procedure with compound visual stimuli was used to train mice to attend to 1 of 2 stimulus dimensions (lines or shapes). On a 2nd problem with new stimuli, the mice were required to attend to the same dimension (intradimensional [ID] shift) or switch to the previously irrelevant dimension (extradimensional [ED] shift). Mice readily learned the initial compound discrimination and following shift problem, but there was no ID-ED difference. The fact that mice can be tested with stimuli and task sequences similar to those used with primates suggests that this method can be used to directly compare higher cognitive functions in diverse species.

Cognitive predictors of dementia in Parkinson's disease: a community-based, 4-year longitudinal study

Although mild cognitive impairment and dementia are common and have important clinical consequences for patients with Parkinson's disease (PD) and their caregivers, it is still unclear whether cognitive symptoms may predict the development of dementia in PD patients. The objective of this study was to determine whether cognitive deficits in nondemented PD patients predicted the development of dementia 4 years later. A total of 76 nondemented PD patients from an epidemiological study of PD in the county of Rogaland, Norway, were assessed at baseline and 4 years later with neurological, psychiatric, and neuropsychological evaluations. Twenty-five (42%) new cases of dementia were diagnosed after 4 years. Time to complete the third card of the Stroop test was the only variable that was independently associated with dementia. The authors concluded that poor performance on a test sensitive to executive dysfunction predicted later development of dementia in PD patients. This finding may have important clinical implications as a marker of subsequent development of dementia.

Selected executive skills in adolescents with recent first episode major depression

BACKGROUND

To investigate whether recent first episode major depression in adolescence is characterised by selected executive difficulties in attentional flexibility, behavioural inhibition and decision-making.

METHODS

Selected executive functions were compared in adolescents with recent (past year) first episode major depression (n = 30) and community controls (n = 49). Three computerised tests within the CANTAB battery were completed by all subjects (the Intra-Dimensional, Extra-Dimensional Set-Shifting task, the Affective Go, No-Go task, and the Decision-Making task).

RESULTS

Compared with controls, recently depressed cases displayed a bias towards negative stimuli with fewer errors on sad words as well as being more accurate in their responses to sad targets on the Affective Go, No-Go task. Cases also made faster decisions in the context of betting more of their available points compared to controls, as indexed by the Decision-Making task. These results were not influenced by age, gender, IQ, recent mood, severity of depression, medication or comorbidity.

CONCLUSIONS

Adolescents with recent first episode major depression show greater attention towards sad stimuli and more impulsive behaviour when making decisions. They were able to switch attentional set to neutral stimuli. This study demonstrates that computerised tests for measuring executive functions can be successfully deployed in adolescents, and suggests that specific patterns of neuropsychological functions may be relatively compromised in first episode major depression. These, together with their underlying neural substrates, deserve further investigation within this age range.

Learning performance on the discrimination-shift task in patients with cortical and subcortical lesions

Patients with brain damage completed reversal and nonreversal shift-learning tasks and we compared their performance with that of normal adults. The overall group differences revealed that many patients could not reach the task criterion regardless of the location of damage and the shift condition of the task. When we compared patients with subcortical and cortical damage, we also found no group differences with regard to the total number of trials required to reach the learning criterion and in terms of their learning processes during shift learning. However, when we compared patients with subcortical and unilateral cortical damage, the results revealed that the learning processes of patients with subcortical damage were normal, whereas the patients with unilateral cortical damage showed lesion-specific effects on shift learning. These findings are discussed in light of previous developmental findings and the proposed role of subcortical structures in learning.

Category learning and multiple memory systems

Categorization is a vitally important skill that people use every day. Early theories of category learning assumed a single learning system, but recent evidence suggests that human category learning may depend on many of the major memory systems that have been hypothesized by memory researchers. As different memory systems flourish under different conditions, an understanding of how categorization uses available memory systems will improve our understanding of a basic human skill, lead to better insights into the cognitive changes that result from a variety of neurological disorders, and suggest improvements in training procedures for complex categorization tasks.

The neuropsychology of normal pressure hydrocephalus (NPH)

Normal pressure hydrocephalus (NPH) accounts for one of the few known forms of reversible dementia. Varied aetiology and clinical presentation contribute to difficulties with early or differential diagnoses, and delayed surgical treatment may be less efficacious. Clinical neuropsychology provides a means of determining a cognitive profile for NPH, assisting in differential diagnosis, tracking the disorder's progression and assessing the efficacy of treatment. This article will review possible applications of clinical neuropsychology and propose a clinical assessment protocol for NPH.

Dopaminergic modulation of cognitive function-implications for L-DOPA treatment in Parkinson's disease

It is well recognised that patients with Parkinson's disease exhibit cognitive deficits, even in the earliest disease stages. Whereas, L-DOPA therapy in early Parkinson's disease is accepted to improve the motor symptoms, the effects on cognitive performance are more complex: both positive and negative effects have been observed. The purpose of the present article is to review the effects of L-DOPA medication in Parkinson's disease on cognitive functions in the broad domains of cognitive flexibility and working memory. The review places the effects in Parkinson's disease within a framework of evidence from studies with healthy human volunteers, rodents and non-human primates as well as computational modeling work. It is suggested that beneficial or detrimental effects of L-DOPA are observed depending on task demands and basal dopamine levels in distinct parts of the striatum. The study of the beneficial and detrimental cognitive effects of L-DOPA in Parkinson's disease has substantial implications for the understanding and treatment development of cognitive abnormalities in Parkinson's disease as well as normal health.

Human Category Learning

Much recent evidence suggests some dramatic differences in the way people learn perceptual categories, depending on exactly how the categories were constructed. Four different kinds of category-learning tasks are currently popular-rule-based tasks, information-integration tasks, prototype distortion tasks, and the weather prediction task. The cognitive, neuropsychological, and neuroimaging results obtained using these four tasks are qualitatively different. Success in rule-based (explicit reasoning) tasks depends on frontal-striatal circuits and requires working memory and executive attention. Success in information-integration tasks requires a form of procedural learning and is sensitive to the nature and timing of feedback. Prototype distortion tasks induce perceptual (visual cortical) learning. A variety of different strategies can lead to success in the weather prediction task. Collectively, results from these four tasks provide strong evidence that human category learning is mediated by multiple, qualitatively distinct systems.

The neurobiology of category learning

Many recent studies have examined the neural basis of category learning. Behavioral neuroscience results suggest that both the prefrontal cortex and the basal ganglia play important category-learning roles; neurons that develop category-specific firing properties are found in both regions, and lesions to both areas cause category-learning deficits. Similar studies indicate that the inferotemporal cortex does not mediate the learning of new categories. The cognitive neuroscience literature on category learning appears contradictory until the results are partitioned according to the type of category-learning task that was used. Three major tasks can be identified: rule based, information-integration, and prototype-distortion. Recent results are consistent with the hypotheses that (a) learning in rule-based tasks requires working memory and executive attention and is mediated by frontal-striatal circuits, (b) learning in information-integration tasks requires procedural memory and is mediated primarily within the basal ganglia, and (c) learning in prototype-distortion tasks depends on multiple memory systems, including the perceptual representation system.

Dopaminergic basis for deficits in working memory but not attentional set-shifting in Parkinson's disease

Although Parkinson's disease is a common neurodegenerative disorder characterised by its motoric symptoms, there is an increasing recognition of accompanying impairments in cognition that have a profound impact on the quality of life of these patients. These deficits predominantly affect executive function and impairments of working memory have been frequently reported. However, the underlying neurochemical and pathological basis for these deficits are not well understood. In this study, 20 patients were tested 'on' and 'off' levodopa (L-dopa) medication on a task that allowed different aspects of working memory function such as maintenance, retrieval and manipulation to be tested within the same general paradigm as well as on an unrelated test of attentional set-shifting, which is known to be sensitive to deficits in early Parkinson's disease. Compared to healthy volunteers, PD patients were impaired at manipulation more than maintenance or retrieval of information within working memory. The patients were also impaired at the attentional set-shifting task. However, whereas L-dopa ameliorated the working memory deficit in manipulation (improving both accuracy and cognitive response time), it had no effect on the attentional set-shifting impairment. These results confirm that working memory deficits in PD are both psychologically specific and related to dopamine depletion. It is anticipated that greater understanding of these mechanisms will lead to future therapeutic improvements.

Lack of inhibition in Parkinson's disease: evidence from a lexical decision task

Persons affected by Parkinson's disease (PD) often show an increased semantic priming effect from target words in lexical decision tasks (hyper-priming) as compared to age-matched controls. In this study, a lexical decision task was used to investigate both semantic priming (Experiment 1) and repetition priming (Experiment 2) from distractor words in PD patients and age-matched controls. With this negative priming procedure, target words in successive trials are never related, and therefore participants always have to switch between unrelated target words. Instead, it is the distractor prime word that is either related or unrelated to the subsequent target, giving the measure of priming. Results showed that PD patients demonstrated a robust effect of positive semantic priming from distractor words. Participants from the control group did not show any semantic priming effect (positive or negative) from distractors. Similarly, PD patients showed positive repetition priming from distractor words, but the control group showed significant repetition negative priming. These results support the view that the hyper-priming effect typically shown by persons with Parkinson's disease is the result of impaired inhibitory processes required to control word activation during reading.

Impaired set-shifting and dissociable effects on tests of spatial working memory following the dopamine D2 receptor antagonist sulpiride in human volunteers

RATIONALE

Dopamine (DA) D(2) receptor antagonists have been shown to produce similar impairments to those seen in Parkinson's disease. These include working memory and set-shifting deficits. Theories of DA function have predicted that distraction or impaired switching may be important determinants of such deficits.

OBJECTIVES

In order to test these hypotheses, we have followed up our previous findings with more refined tests (1) that allow measurement of spatial working memory (SWM) and distraction, (2) that allow separation of executive and mnemonic components of SWM and (3) that allow isolation of set-shifting from learning deficits.

METHODS

Thirty-six young healthy male volunteers were tested on two occasions after oral administration of either 400 mg sulpiride or placebo. All participants performed the delayed response task. Sixteen participants received task-irrelevant distractors during this task, and were also given a self-ordered SWM test. The remaining participants were given delayed response tasks with task-relevant distractors, and tests of attentional and task set-shifting.

RESULTS

Sulpiride impaired performance of the delayed-response task both without distraction and with task-relevant distraction. By contrast, the drug protected against deficits from task-irrelevant distraction seen in the placebo group. Task set-switching was also impaired by sulpiride, with participants being slower to respond on switch trials compared with non-switch trials. There was also a trend for attentional set-shifting to be impaired following sulpiride. In contrast, self-ordered SWM performance was enhanced by sulpiride on the second test session only.

CONCLUSIONS

These results support models of central DA function that postulate a role in switching behaviour, and in certain aspects of working memory.

Endocrine disruption and cognitive function in adolescent female rhesus monkeys

Female rhesus monkeys (n=8/group) received daily oral doses of exogenous estrogen [diethylstilbestrol (DES), 0.5 mg/kg, methoxychlor (MXC), 25 or 50 mg/kg] for 6 months before and after the anticipated age of menarche. Behavior was assessed during and for 9 months after dosing. Visual discrimination performance (simultaneous nonmatch-to-sample with trial-unique stimuli) conducted during dosing demonstrated delayed improvement and poorer performance in the MXC50 group, with some similar effects in the DES group. Visual recognition memory, assessed with delays of < or = 3 s, was not apparently affected. Spatial working memory, assessed after dosing, also showed acquisition deficits and possible working memory difficulties in the MXC50 group. Spontaneous motor activity, monitored at 6-month intervals, was not affected by treatment. Late peak latencies of the auditory brainstem response (ABR) were shorter in the DES group 6 months after treatment, suggesting long-term effects on brain. The study suggests that some aspects of brain function can be modified by exposure to exogenous estrogen during pubertal development. Although DES is a more potent estrogen, the high-dose MXC group was more affected behaviorally. Differential effects of the two agents at the estrogen receptor subtypes (ER alpha and ER beta) may be relevant to the differential behavioral outcomes.

Catechol-o-methyltransferase inhibition improves set-shifting performance and elevates stimulated dopamine release in the rat prefrontal cortex

The Val158Met polymorphism of the human catechol-O-methyltransferase (COMT) gene affects activity of the enzyme and influences performance and efficiency of the prefrontal cortex (PFC); however, although catecholaminergic neurotransmission is implicated, the underlying mechanisms remain elusive because studies of the role of COMT in PFC function are sparse. This study investigated the effect of tolcapone, a brain-penetrant COMT inhibitor, on a rat model of attentional set shifting, which is dependent on catecholamines and the medial PFC (mPFC). Additionally, we investigated the effect of tolcapone on extracellular catecholamines in the mPFC using microdialysis in awake rats. Tolcapone significantly and specifically improved extradimensional (ED) set shifting. Tolcapone did not affect basal extracellular catecholamines, but significantly potentiated the increase in extracellular dopamine (DA) elicited by either local administration of the depolarizing agent potassium chloride or systemic administration of the antipsychotic agent clozapine. Although extracellular norepinephrine (NE) was also elevated by local depolarization and clozapine, the increase was not enhanced by tolcapone. We conclude that COMT activity specifically affects ED set shifting and is a significant modulator of mPFC DA but not NE under conditions of increased catecholaminergic transmission. These data suggest that the links between COMT activity and PFC function can be modeled in rats and may be specifically mediated by DA. The interaction between clozapine and tolcapone may have implications for the treatment of schizophrenia.

Attentional cueing reverses deficits in spatial working memory task performance in chronic low dose MPTP-treated monkeys

Chronic low dose MPTP-treated monkeys develop difficulty in performing spatial working memory tasks. Since these tasks have both attentional and memory components, the extent to which task performance deficits are attentional or memory in nature was examined. Using a modified variable delayed response (VDR) task, employment of an attentional cue prior to stimulus presentation significantly improved task performance, suggesting a strong attentional component to the deficit in spatial working memory task performance. These findings suggest that procedures to enhance attention may be useful in ameliorating some of the "memory" deficits associated with early Parkinson's disease.

Attention and executive function deficits in chronic low-dose MPTP-treated non-human primates

Parkinson's disease (PD) is a complex disorder consisting of motor deficits coupled with dysfunction in cognitive domains that are dependent upon the integrity of the frontal lobes and/or the fronto-striatal axis. Although it is increasingly acknowledged that PD patients have attentional and executive function deficits, it has been difficult to model these in nonhuman primates because of the nature of the cognitive tasks that have been used previously. The present studies were conducted to further define the nature of the cognitive impairment in a nonhuman primate model of early parkinsonism consequent to chronic low dose MPTP exposure and to further validate this model in monkeys trained to perform a battery of attentional and executive function tasks. Following chronic low dose MPTP exposure, monkeys developed deficits in maintenance of a response set as well problems in shifting attentional sets, suggesting decreased mental flexibility. On other tasks inattentiveness, an impaired ability to sustain spatial attention or to focus attention, a deficit in motor readiness and planning, and impaired time estimation were also observed. These results provide direct evidence of attention and executive function deficits in a nonhuman primate model of early parkinsonism. Based on these findings, we suggest that in addition to being useful for studying the cognitive deficits related to early PD and for developing new therapeutics for these problems, this model and these testing procedures may also provide a useful large animal model for studying attention deficit disorder and for developing new therapeutics for that condition as well.

Discriminations, reversals, and extra-dimensional shifts in the Göttingen minipig

Göttingen minipigs were trained on a set-shifting procedure involving discriminations, reversals, and extra-dimensional shifts. The discriminations used were black-white discriminations and right-left discriminations. The initial visual and spatial discrimination seemed equally difficult, and only for the visual modality was reversal found to be more difficult than the initial discrimination. Visual reversal was more difficult than spatial reversal, and a larger number of perseverative sessions were found for visual reversal compared to spatial reversal. The acquisition of the extra-dimensional shift from the visual to the spatial dimension was not inferior to the learning of spatial reversal. Neither was the acquisition of the extra-dimensional shift from the spatial to the visual dimension inferior to the learning of visual reversal. Thus, no evidence was found for attention to stimulus dimensions in discrimination learning of the pigs.

Neurocognitive elements of antisocial behavior: Relevance of an orbitofrontal cortex account

This paper reviews the role of orbitofrontal cortex (OFC) lesions in antisocial behaviors and the adequacy of a strict OFC account of antisocial disorders where there is no evidence of lesion. Neurocognitive accounts of antisocial behaviors are extended beyond the OFC. Several methodological shortcomings specific to this neuroscience approach to antisocial behavior are identified. A developmental approach is advocated to chart the developmental sequences of impaired brain development and of the various comorbid states typically seen in antisocial disorders.

Effects of amisulpride, risperidone and chlorpromazine on auditory and visual latent inhibition, prepulse inhibition, executive function and eye movements in healthy volunteers

In view of the evidence that cognitive deficits in schizophrenia are critically important for long-term outcome, it is essential to establish the effects that the various antipsychotic compounds have on cognition, particularly second-generation drugs. This parallel group, placebo-controlled study aimed to compare the effects in healthy volunteers (n = 128) of acute doses of the atypical antipsychotics amisulpride (300 mg) and risperidone (3 mg) to those of chlorpromazine (100 mg) on tests thought relevant to the schizophrenic process: auditory and visual latent inhibition, prepulse inhibition of the acoustic startle response, executive function and eye movements. The drugs tested were not found to affect auditory latent inhibition, prepulse inhibition or executive functioning as measured by the Cambridge Neuropsychological Test Battery and the FAS test of verbal fluency. However, risperidone disrupted and amisulpride showed a trend to disrupt visual latent inhibition. Although amisulpride did not affect eye movements, both risperidone and chlorpromazine decreased peak saccadic velocity and increased antisaccade error rates, which, in the risperidone group, correlated with drug-induced akathisia. It was concluded that single doses of these drugs appear to have little effect on cognition, but may affect eye movement parameters in accordance with the amount of sedation and akathisia they produce. The effect risperidone had on latent inhibition is likely to relate to its serotonergic properties. Furthermore, as the trend for disrupted visual latent inhibition following amisulpride was similar in nature to that which would be expected with amphetamine, it was concluded that its behaviour in this model is consistent with its preferential presynaptic dopamine antagonistic activity in low dose and its efficacy in the negative symptoms of schizophrenia.

The neuropsychology of ventral prefrontal cortex: Decision-making and reversal learning

Converging evidence from human lesion, animal lesion, and human functional neuroimaging studies implicates overlapping neural circuitry in ventral prefrontal cortex in decision-making and reversal learning. The ascending 5-HT and dopamine neurotransmitter systems have a modulatory role in both processes. There is accumulating evidence that measures of decision-making and reversal learning may be useful as functional markers of ventral prefrontal cortex integrity in psychiatric and neurological disorders. Whilst existing measures of decision-making may have superior sensitivity, reversal learning may offer superior selectivity, particularly within prefrontal cortex. Effective decision-making on existing measures requires the ability to adapt behaviour on the basis of changes in emotional significance, and this may underlie the shared neural circuitry with reversal learning.

Advance preparation of set-switches in Parkinson's disease

Eighteen patients with Parkinson's disease (PD) and 18 healthy control subjects were presented with a switching task where stimuli elicited either one (no-conflict condition) or two (conflict condition) task-relevant stimulus-response mappings. The response stimulus interval (RSI) between trials was varied to allow investigation of the extent to which participants engaged in advanced preparation of task set. In line with previous findings, set-switching deficits of PD patients were only observed in the conflict condition. Prolonging the RSI led to a reduction of switch costs for control subjects in both the conflict and the no-conflict task, whereas this effect was attenuated for PD patients in the conflict condition. This deficit was explained in terms of a reduced ability to maintain cue-action representations active in working memory in high interference conditions, and was related to the possible role of the frontostriatal circuit in maintaining focussed attention.

Diazepam produces disinhibitory cognitive effects in male volunteers

RATIONALE

Diazepam has well known amnestic and sedative effects but effects on fronto-executive function remain largely uninvestigated, especially on neuropsychologically validated tests of risk taking and orbitofrontal cortex function.

OBJECTIVES

We aimed to determine the impact of diazepam on a variety of executive tasks.

METHODS

The effects of 5, 10 and 20 mg of diazepam on a battery of neuropsychological tests were investigated using a randomised, double blind, placebo-controlled design. Seventy-five adult men were recruited. The Rogers et al. (1999b) test of risk-taking was given along with tasks from the CANTAB battery.

RESULTS

Diazepam impaired performance on the Tower of London test of planning, without influencing visual pattern recognition memory. Subjects who had taken diazepam made more risky choices on the risk-taking task. On two speeded reaction time tasks diazepam impaired discrimination sensitivity and increased the bias to respond.

CONCLUSIONS

In contrast to the well-known sedative effects of diazepam, we demonstrate disinhibitory effects on two speeded reaction time tasks. Our results show that diazepam can impair performance on reaction time tasks both by impairing sensitivity and by increasing the bias to respond. Furthermore diazepam impaired performance on tests of planning and risky decision making that depend predominantly on dorsolateral and orbitofrontal regions of the prefrontal cortex, respectively.

Striatal contributions to working memory: a functional magnetic resonance imaging study in humans

Although the role of the frontal cortex in executive performance has been widely accepted, issues regarding the contribution of subcortical structures to these functions remain unresolved. In this study, the neural circuitry underlying selective subcomponents of working memory was investigated using event-related functional magnetic resonance imaging (fMRI). Ten healthy volunteers performed a verbal memory task, which allowed different aspects of working memory function such as maintenance, retrieval and manipulation to be tested within the same general paradigm. During performance of this task as a whole, fMRI revealed increases in signal intensity throughout the frontostriatal network. However, when signal intensity during the manipulation of information within working memory was compared to that during periods requiring only simple maintenance and retrieval, significant changes were observed only in the caudate nuclei, bilaterally. These results suggest an essential and specific role for the caudate nucleus in executive function, which may underlie the cognitive disturbances observed in frontostriatal neurodegenerative disorders such as Parkinson's disease.

Methylphenidate improves working memory and set-shifting in AD/HD: relationships to baseline memory capacity

OBJECTIVE

Catecholamine stimulant drugs are highly efficacious treatments for attention deficit/ hyperactivity disorders (AD/HD). Catecholamine modulation in humans influences performance of numerous cognitive tasks, including tests of attention and working memory (WM). Clear delineation of the effects of methylphenidate upon such cognitive functions in AD/HD would enhance understanding of the effects of drug treatment.

METHOD

Here we present a double-blind, placebo-controlled study of the cognitive effects of an acute dose of methylphenidate (c. .5 mg/kg) in 14 boys aged 10.86 (+/- 1.19) years meeting criteria for DSM-IV AD/HD. Current behaviour was ascertained using Conners' teacher and parent self-report questionnaires and IQ was tested using sub-tests from WISC-III-UK. Tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB) were selected to assess visuo-spatial recognition memory, spatial WM, planning, visual-search and attentional-set shifting.

RESULTS

Methylphenidate improved spatial WM, attentional-set shifting and visual-search task performance. Correlational analyses suggested possible relationships between WM capacity and spatial WM performance improvement. Also, poor performance on the attentional-set shifting task on placebo was associated with increased errors on the spatial WM task on placebo.

CONCLUSIONS

Methylphenidate may selectively improve both underlying cognitive difficulties in tasks dependent on intact fronto-striatal structures, and clinical symptoms of AD/HD. Pre-treatment measures may have some predictive value in determining individual differences in drug response.

Orbital prefrontal cortex mediates reversal learning and not attentional set shifting in the rat

It has been demonstrated previously that lesions to medial prefrontal cortex in rats impair the shifting of attentional set between perceptual features of complex stimuli [J. Neurosci. 20 (2000) 4320], a result that mirrors the deficit found in humans and monkeys [Nature 380 (1996) 69; Behav. Neurosci. 110 (1996) 872; J. Neurosci. 17 (1997) 9285; Neuropsychologia 29 (1991) 993]. These data imply functional homology between rat medial prefrontal cortex and primate prefrontal cortex.In marmoset monkeys, there is a double dissociation between the effects of lesions of lateral prefrontal cortex, which impair shifting of attentional set, and lesions of orbital prefrontal cortex, which result in impairments of reversal of stimulus-reward contingencies, leaving attentional set-shifting capacities intact [Nature 380 (1996) 69; Behav. Neurosci. 110 (1996) 872; J. Neurosci. 17 (1997) 9285]. The present investigation examined whether lesions to rat orbital prefrontal cortex would produce deficits in reversal learning in the absence of deficits in shifting attentional set, as seen in monkeys. Rats were trained to perform an attentional set-shifting task that is formally the same as that used in monkeys and humans. In a single session, rats performed a series of discriminations, including acquisitions and reversals. Damage to orbital prefrontal cortex in the rats did not disrupt the ability to acquire, maintain or shift attentional set. We report here the same selective impairment in reversal learning in rats as seen in primates with orbital prefrontal cortex lesions.

Role of the Basal Ganglia in Category Learning: How Do Patients With Parkinson's Disease Learn?

The purpose of the present study was to gain a deeper understanding of the role of the basal ganglia in learning and memory by examining learning strategies among patients with basal ganglia dysfunction. Using a probabilistic category learning task (the "weather prediction" task) previously shown to be sensitive to basal ganglia function, the authors examined patterns of performance during learning and used mathematical models to capture different learning strategies. Results showed that patients with Parkinson's disease exhibit different patterns of strategy use. Specifically, most controls initially used a simple, but suboptimal, strategy that focused on single-cue-outcome associations; eventually, however, most controls adopted a more complex, optimal learning strategy, integrating single-cue associations to predict outcomes for multiple-cue stimuli. In contrast, the majority of individuals with Parkinson's disease continued to rely on simple single-cue learning strategies throughout the experiment.