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

A specific shifting deficit in Parkinson's disease: a reversal shift of consistent stimulus-response mappings

Two experiments were designed to investigate effects of cueing upon aptitude for shifting by patients with Parkinson's disease. Subjects executed in alternation two different components of a task set over successive items in a list. We compared the costs of shifting when the stimulus ensemble remained constant from trial to trial ("uniform" lists), with the case in which a change of stimulus ensemble cued each shift of task ("mixed" lists). Shift costs with mixed lists were significantly smaller than those with uniform lists (Exp. 1, ns = 12). This suggests that patients with Parkinson's disease can benefit from cues about the stimulus ensemble in performing tasks. Patients' shifting performance was different from that of controls only in a reversal-shift condition of the previously consistent stimulus-response mappings (Exp. 2, ns = 12). This result suggests that patients with Parkinson's disease suffer from a specific but not a general deficit in ability to shift.

Reaction time deficits and Parkinson's disease

Controversy surrounds the existence and nature of reaction time deficits in Parkinson's disease. Three areas of research are reviewed: the use of precues to speed movement (motor preprogramming), the effects of medication on reaction time, and simple reaction times. No evidence is found for a motor preprogramming deficit, and the presence of a parkinsonian reaction time deficit after medication withdrawal is found to be dependent upon experimental design and the withdrawal method used. Parkinson's disease is found to cause a consistent deficit in simple reaction time. A quantitative analysis of past studies reveals that a parkinsonian reaction time deficit is more likely to be present in tasks that controls can perform with a fast reaction time. This relationship between deficit and control group reaction time applies to choice, but not simple, reaction time tasks. Many studies compare patient and control choice reaction times across experimental conditions that cause control reaction time to vary. The authors of these studies should consider whether their results can be explained in terms of the simple relationship between patient reaction time deficit and control reaction time before drawing more complex conclusions from their data.

Test/re-test reliability of the CANTAB and ISPOCD neuropsychological batteries: theoretical and practical issues. Cambridge Neuropsychological Test Automated Battery. International Study of Post-Operative Cognitive Dysfunction

Neuropsychological test batteries are repeatedly administered to evaluate changes over time or the effects of clinical interventions. Relationships between scores on different tests within batteries are also examined to test models for associations between functional deficits. These comparisons may be misleading unless Test/Re-test reliability for individual tests is satisfactory. Interpretations of repeated measurements also depend on the extent to which improvement with practice varies between tasks and between more and less able individuals. Test/Re-test correlations and practice effects for two neuropsychological test batteries (CANTAB, ISPOCD) and from laboratory tasks commonly used in cognitive assessments of older people were obtained from large groups of healthy elderly. Tests in neuropsychological batteries varied markedly in test/re-test reliability which, in some cases, fell below levels considered methodologically acceptable. Putative measures of 'frontal' or 'executive' function, in which performance may be markedly improved by abrupt discovery of an appropriate strategy, were especially likely to show low reliability. Most tests showed significant practice effects, and on some these are substantial enough to compromise comparisons on repeated testing. On a minority of tests practice effects were counter-intuitive, in that less able showed significantly more gains than more able individuals.

Neural Systems Underlying Arousal and Attention: Implications for Drug Abusea

The monoaminergic and cholinergic systems are implicated in different forms of behavioral arousal that can be dissected in terms of their forebrain targets and the nature of the behavioral processes they modulate in distinct regions. Thus, evidence in rats with selective neurochemical manipulations tested behaviorally using an analog of an attentional task developed for human subjects indicates that the coeruleo-cortical noradrenergic system is implicated in divided and selective attention, the basal forebrain cholinergic system in stimulus detection, the mesostriatal and mesolimbic dopaminergic systems in response speed and vigor, and the mesencephalic serotoninergic or 5-HT systems in response inhibition. Our recent studies have focused on fractionating, in the same task, the differential contributions of the dorsal and median raphé 5-HT systems as well as elucidating the functions of the mesocortical dopaminergic system, each of which may be relevant to understanding the behavioral and cognitive sequelae of cocaine administration in human subjects as well as in experimental animals.

Cognitive deficits in obsessive-compulsive disorder on tests of frontal-striatal function

BACKGROUND

Although neuropsychological and neuroimaging studies of obsessive-compulsive disorder (OCD) have implicated the frontal cortex and subcortical structures in the pathophysiology of the disorder, few studies have examined cognitive function in patients with OCD on tasks validated in the assessment of frontal lobe and subcortical dysfunction.

METHODS

The accuracy and latency of executive and visual memory function was assessed in 23 nondepressed OCD patients and 23 normal healthy controls matched for age, sex, education, and estimated IQ.

RESULTS

The patients with OCD performed within the normal range on tasks of short-term memory capacity, delay dependent visual memory, pattern recognition, attentional shifting, and planning ability; however, specific cognitive deficits related to spatial working memory, spatial recognition, and motor initiation and execution were observed in the patient group. These deficits were not correlated with aspects of the patients' intellectual functioning or comorbid psychological symptoms, suggesting that the impairments were related to the specific clinical features of OCD.

CONCLUSIONS

Patients with OCD showed specific cognitive deficits on tasks of executive and visual memory function. The pattern of impaired performance in these patients was qualitatively similar to the performance of patients with frontal lobe excisions and subcortical pathology on the same test battery, suggesting that the underlying pathophysiology of the disorder could best be conceptualized as reflecting dysfunction of frontal-striatal systems.

Toward a functional analysis of the basal ganglia

Parkinson patients were tested in two paradigms to test the hypothesis that the basal ganglia are involved in the shifting of attentional set. Set shifting means a respecification of the conditions that regulate responding, a process sometimes referred to as an executive process. In one paradigm, upon the appearance of each stimulus, subjects were instructed to respond either to its color or to its shape. In a second paradigm, subjects learned to produce short sequences of three keypresses in response to two arbitrary stimuli. Reaction times were compared for the cases where set either remained the same or changed for two successive stimuli. Parkinson patients were slow to change set compared to controls. Parkinson patients were also less able to filter the competing but irrelevant set than were control subjects. The switching deficit appears to be dopamine based; the magnitude of the shifting deficit was related to the degree to which 1-dopa-based medication ameliorated patients' motor symptoms. Moreover, temporary withholding of medication, a so-called off manipulation, increased the time to switch. Using the framework of equilibrium point theory of movement, we discuss how a set switching deficit may also underlie clinical motor disturbances seen in Parkinson's disease.

The functional emergence of prefrontally-guided working memory systems in four- to eight-year-old children

The neural processes that underlie the functional emergence of human cognitive functions, particularly those associated with the prefrontal cortex (PFC), are of growing interest to developmental psychologists and neuroscientists. Specifically, working memory functions have been correlated with PFC activity in nonhuman primates and adult humans but have not been extensively studied in children. We examined the developmental emergence of functions involved in working memory through the use of the Cambridge Neuropsychological Test Automated Battery (CANTAB), a computerized battery of nonverbal visually-presented neuropsychological tests designed to dissociate frontal from temporal lobe behavioral functions. Participants were normal children, aged 4-8 (n = 181) and a small group of young adults (n = 24) who completed measures of Spatial Memory Span, Spatial Working Memory, the Tower of London planning task, Visual Pattern and Spatial Recognition tasks, and a Set-Shifting task. Findings indicate a general age-related progression in ability levels on frontal lobe tasks, with 4-year-olds performing worse than 5- to 7-year-olds on all measures. Eight-year-olds are superior to younger children in their ability to solve complex problems but have not yet reached adult levels of performance on the most difficult items of the Tower of London and Spatial Working Memory tasks. We conclude that the development of working memory functions proceeds dimensionally, starting with refinement of basic perceptual and sensorimotor functions and culminating with the physiological maturation of widespread neural networks that integrate complex processing demands inherent to working memory tasks.

Concurrent monitoring of EEG and performance in the common marmoset: a methodological approach

A model has been developed in a nonhuman primate, the common marmoset (Callithrix jacchus), which should enable the study of long term effects of compounds with potentially psychoactive properties. The technique facilitates concurrent monitoring of both behavioral and electrophysiological parameters while animals remain in their home cages. Subjects were trained to perform tests from a neuropsychological test battery (The Cambridge Neuropsychological Test Automated Battery, CANTAB) in which they learned to discriminate between pairs of stimuli presented on a touch sensitive computer screen. Single channel cortical electroencephalography (EEG) by radiotelemetry was simultaneously recorded while behavioral testing took place.

Neuropsychological prediction of dementia in Parkinson's disease

OBJECTIVE

To identify neuropsychological characteristics predictive of later dementia in Parkinson's disease.

METHODS

A comprehensive neuropsychological test battery was administered to a cohort of 89 initially non-demented patients with Parkinson's disease consecutively enrolled at a specialised Parkinson's disease clinic. They were reassessed after a mean of 3.5 years for the diagnosis of dementia. The Cox proportional hazards model was used to identify baseline characteristics predictive of dementia.

RESULTS

Only four of the baseline clinical characteristics of Parkinson's disease and neuropsychological variables remained independently linked to subsequent development of dementia: the age of onset of Parkinson's disease (>60 years; relative risk (RR) 4.1, 95% confidence interval (95% CI) 1.8-24.0, p<0.03), the picture completion subtest of the Wechsler adult intelligence scale (score<10; RR 4.9, 95% CI 1.0-24.1, p<0.02), the interference section of the Stroop test (score<21; RR 3.8, p=0.08), and a verbal fluency task (score<9; RR 2.7, 95% CI 0.8-9.1, p=0.09). Depressive symptoms and the severity of motor impairment were not predictive of dementia.

CONCLUSION

These features are different from the neuropsychological characteristics predictive of Alzheimer's dementia in healthy elderly people (mainly memory and language performance). They are in keeping with the well known specificity of the impairments in Parkinson's disease for visuospatial abilities and difficulties in inhibiting irrelevant stimuli. It is postulated that the composite nature of the picture completion subtest, involving several cognitive abilities impaired in Parkinson's disease, explains its sensitivity.

Object-based and location-based shifting of attention in Parkinson's disease

Research into Parkinson's disease has made much use of the precuing paradigm developed by Posner to examine patients' ability to shift visuospatial attention. The majority of studies indicate that patients with Parkinson's disease have significantly reduced shift costs when compared with normal controls. This reduction in costs is ascribed to abnormal maintenance of attention resulting from Parkinson's disease. We know that visual attention is not directed to spatial locations alone but that it may also be directed to object representations. To date, however, it has not been clear whether the reduced shift costs apparent in Parkinson's disease patients are evident only on spatial locations or on both spatial locations and object representations. Therefore, in the current study we have adopted a new technique with a view to studying both location-based and object-based attentional components within the same paradigm. Our results with 17 patients with Parkinson's disease suggest, at least in the early stages, patients do not show deficits in maintenance of attention to the miscued source of stimulation as reflected in their normal magnitude of cuing effect related to shifting between locations and between objects. 14 normal persons were control subjects.

Cognitive planning in humans: neuropsychological, neuroanatomical and neuropharmacological perspectives

In recent years, considerable progress has been made in understanding the cognitive and neuroanatomical basis of high-level planning behaviour through a combination of neuropsychological, neuropharmacological and functional neuroimaging approaches. In this article, early evidence suggesting a relationship between planning impairments and damage to the frontal lobe is reviewed and several contemporary studies of planning behaviour in patients with circumscribed frontal lobe excisions are described in detail. These neuropsychological investigations, together with recent functional neuroimaging studies of normal control subjects, have identified a specific area within the mid-dorsolateral frontal cortex of humans which appears to be critically involved in the cognitive processes that mediate efficient planning. The functions of this region, both in cognitive planning and in related functions such as working memory, are then discussed in the context of a general theoretical framework for understanding the functional organization of "executive" processes within the human lateral frontal cortex. In the final sections, the relationship between the planning deficits observed after intrinsic frontal lobe damage and those exhibited by patients with neuropathology of primarily sub-cortical origin, such as Parkinson's disease, is discussed. A central model for much of this work has been the concept of cortico-striatal circuitry which emphasizes the relationship between the neocortex and the striatum. The combined evidence from comparative studies in patients and from functional neuroimaging studies on Parkinson's disease suggests that altered cortico-striatal interactions may disrupt normal planning function at a number of levels, possibly consequent upon intrinsic striatal pathology on the one hand and the partial loss of (frontal) cortical input to the basal ganglia on the other.

Stimulus dimension shifts in patients with schizophrenia, with and without paranoid hallucinatory symptoms, or obsessive compulsive disorder: strategies, blocking and monoamine status

Reversal, and intra-dimensional (ID) and extra-dimensional (ED) nonreversal discrimination shifts were studied to see if learned inattention to the irrelevant dimension differentially influenced the efficacy of learning and stimulus choice strategy. Performance was compared with conditioned blocking (CB) and monoamine metabolic status between healthy controls, patients with obsessive compulsive disorder (OCD) or schizophrenia with (PH) or without (NP) active paranoid hallucinatory symptoms. PH and NP patients improved learning with practice, but showed an impaired shift on each task. OCD patients were impaired only on the ED-shift. The NP patient's impairment was nonspecific and, unlike PH and controls, it related to reversal performance. All subjects acquired an attentional set for colour reflected in the length of stimulus-response sequences. Analysis of paired-stimulus choice-strategies showed that while all patients showed fewer correct win-stay choices, only PH patients perseverated with lose-stay choices. Learning about the added stimulus in the CB task related to ID-shift efficiency in NP patients. Increases of dopamine activity related to delayed learning but more switches of stimulus choice in the shift-tasks. Increases of serotonin activity correlated with faster learning in controls, OCD and PH patients. In NP patients the opposite held for dopamine and serotonin activity. Thus the two learned inattention tasks have different if related requirements and correlates: the data are consistent with the use of automatic exogenous attention strategies by NP patients, of inefficient controlled attention by PH patients and the automatization of endogenous processes in controls.

Hallucinosis in idiopathic Parkinson's disease

BACKGROUND

Hallucinosis is a complication of the treatment of idiopathic Parkinson's disease commonly thought to afflict older, chronically medicated, cognitively impaired patients. However, patients with idiopathic Parkinson's disease of short duration experiencing hallucinosis on relatively low doses of dopaminergic medication have been found. The aim, therefore, was to investigate the homogeneity of a population of patients with idiopathic Parkinson's disease and hallucinosis.

METHODS

The clinical, demographic, and cognitive correlates of hallucinosis were investigated in a sample of 129 patients with idiopathic Parkinson's disease.

RESULTS

There were two subgroups of patients with idiopathic Parkinson's disease experiencing hallucinosis. In patients with a disease duration of five years or less, hallucinosis was associated with rapid progression of the motor component of the disease but not cognitive impairment. In patients with idiopathic Parkinson's disease of longer than five years duration, hallucinosis was associated with postural instability, global cognitive impairment, and lack of depressive affect. In all patients with idiopathic Parkinson's disease, hallucinosis was more prevalent when they were treated with a direct acting dopamine receptor agonist. Hallucinosis was not associated with age at onset of idiopathic Parkinson's disease or dosage of dopaminergic medication.

CONCLUSION

Hallucinosis in idiopathic Parkinson's disease is heterogeneous, falling into two groups. The difference in the pathophysiological basis of hallucinosis in these two groups of patients is discussed.

Deductive and inductive reasoning in Parkinson's disease patients and normal controls: review and experimental evidence

In the present study, fifty-four subjects were tested; twenty-seven with idiopathic Parkinson's disease and twenty-seven normal controls matched in age, education, verbal ability, level of depression, sex and socio-economic status. The subjects were tested on eight tasks. Five of the tasks were the classic deductive reasoning syllogisms, modus ponens, modus tollendo tollens, affirming the consequent, denying the antecedent and three-term series problems phrased in a factual context (brief scripts). Three of the tasks were inductive reasoning, including logical inferences, metaphors and similes. All tasks were presented to subjects in a multiple choice format. The results, overall, have shown nonsignificant differences between the two groups in deductive and inductive reasoning, an ability traditionally associated with frontal lobes involvement. Of the comparisons performed between subgroups of the patients and normal controls concerning disease duration, disease onset and predominant involvement of the left and/or right hemisphere, significant differences were found between patients with earlier disease onset and normal controls and between bilaterally affected patients and normal controls, demonstrating an additive effect of lateralization to reasoning ability.

Spatial and non-spatial working memory at different stages of Parkinson's disease

Groups of patients with Parkinson's disease, either medicated or unmedicated, were compared with a matched group of normal control subjects on a computerized battery of tests designed to assess spatial, verbal and visual working memory. In the spatial working memory task, subjects were required to search systematically through a number of boxes to find 'tokens' whilst avoiding those boxes in which tokens had previously been found. In the visual and verbal conditions, the subjects were required to search in exactly the same manner, but through a number of abstract designs or surnames, respectively, avoiding designs or names in which a token had previously been found. Medicated Parkinson's disease patients with severe clinical symptoms were impaired on all three tests of working memory. In contrast, medicated patients with mild clinical symptoms were impaired on the test of spatial working memory, but not on the verbal or visual working memory tasks. Non-medicated patients with mild clinical symptoms were unimpaired on all three tasks. These data are compared with the results of a previous study comparing groups of neurosurgical patients with frontal, temporal or amygdalo-hippocampectomy excisions on the same three tests of working memory. Taken together, the findings suggest that working memory deficits in Parkinson's disease emerge, and subsequently progress, according to a defined sequence, the evolution of which may be linked to the likely spatiotemporal progression of dopamine depletion within the striatum, in relation to the terminal distribution of its cortical afferents.

Sensory and cognitive functions of the basal ganglia

Recent studies have found that the basal ganglia are involved in diverse behavioral activities and suggest that they have executive functions. Highlights from the past year include anatomical and clinical studies that have used sophisticated, novel methods to confirm a role for the basal ganglia in somatosensory discrimination, visual perception, spatial working memory and habit learning.

Uncomplicated carotid endarterectomy is not associated with neuropsychological impairment

Whether neuropsychological changes follow carotid artery surgery is unclear, in part because of complications by multiple perioperative variables. Therefore, we carried out a detailed analysis of patients who underwent carotid artery surgery in which we attempted to control for the most important variables by excluding patients with a preoperative stroke and by adopting a standard operative technique without use of intraoperative carotid shunts. Thirty inpatients with symptomatic carotid artery disease admitted for carotid endarterectomy were assessed with a comprehensive battery of neuropsychological tests administered immediately before and after (48-72 h) surgery. No carotid bypass shunt was inserted during the operation. The battery included dementia and depression screening tests, standardised neuropsychological measures including Verbal Fluency and the National Adult Reading Test, and a battery of contemporary computerised tasks designed to measure different aspects of memory and attention from the Cambridge Neuropsychological Test Automated Battery (CANTAB). No significant difference was found in the cognitive scores postoperatively as compared with the patients' preoperative scores or compared with scores of a control group matched by age and intelligence.

Memory for spatial location in 'de novo' parkinsonian patients

A deficit in memory for spatial location was recently reported in typical non-demented parkinsonian patients ('standard'). Is this deficit related to dopamine depletion? Such an association would reinforce the suggestion that striato-frontal neuronal circuits are implicated in memory for item-specific spatial coordinates. To answer this question, we compared the performance of 10 recently diagnosed and not yet treated parkinsonian patients ('de novo'), in which the neurobiochemical deficit is considered to involve mainly the nigrostriatal dopaminergic system, to that of 14 controls matched for age, global cognitive efficiency and mood, on a visuospatial learning test. The task required little motor or constructive functions and was designed to allow control of encoding and comparison of free recall, cued recall and recognition. Compared to controls, 'de novo' patients displayed a lower performance in memory for visuospatial location of pictures, contrasting with relative preservation of verbal memory, perceptive visuospatial and executive functions. These results confirm the sensitivity of visuospatial memory even at an early stage of Parkinson's disease and suggest the implication of the nigrostriatal dopaminergic system, and associated striato-frontal neuronal circuits, in executive processes needed for spatial location learning.

Specific cognitive deficits in tests sensitive to frontal lobe dysfunction in obsessive-compulsive disorder

Forty patients with obsessive-compulsive disorder (OCD) were compared to matched healthy controls on neuropsychological tests which are sensitive to frontal lobe dysfunction. On a computerized version of the Tower of London test of planning, the patients were no different from healthy controls in the accuracy of their solutions. However, when they made a mistake, they spent more time than the controls in generating alternative solutions or checking that the next move would be correct. The results suggest that OCD patients have a selective deficit in generating alternative strategies when they make a mistake. In a separate attentional set-shifting task, OCD patients were impaired in a simple discrimination learning task and showed a continuous cumulative increase in the number who failed at each stage of the task, including the crucial extradimensional set shifting stage. This suggests that OCD patients show deficits in both acquiring and maintaining cognitive sets. The cognitive deficits in OCD may be summarized as: (i) being easily distracted by other competing stimuli; (ii) excessive monitoring and checking of the response to ensure a mistake does not occur; and (iii) when a mistake does occur, being more rigid at setting aside the main goal and planning the necessary subgoals. Both studies support the evidence of fronto-striatal dysfunction in OCD and the results are discussed in terms of an impaired Supervisory Attentional System.

Dissociating executive functions of the prefrontal cortex

An analysis is provided of three distinct paradigms that have been used to study executive functions of the prefrontal cortex involving planning, self-ordered memory or attentional set-shifting. Psychological and anatomical dissociations are sought from the perspective of studies of patients with frontal lobe lesions, functional neuroimaging, psychometric studies in normal volunteers and experimental studies in non-human primates. Particular attention is paid to attempts to dissociate mnemonic from other executive capacities. Thus, patients with frontal damage are shown to have deficits in their (1) use of strategies to improve performance in a spatial working memory task and (2) capacity to make an extra-dimensional shift due to a high-order failure of inhibition in an attentional set-shifting paradigm. These results are discussed in terms of anatomical and neuropharmacological dissociations of different aspects of executive function within the prefrontal cortex shown in monkeys.

Neuropsychological impairments in unipolar depression: the influence of perceived failure on subsequent performance

The CANTAB battery of neuropsychological tests was used to compare the performance of 28 patients with unipolar depression with that of 22 age and IQ matched controls. The patients were impaired on almost all tests studied with deficits in pattern and spatial recognition memory, matching to sample, spatial span, spatial working memory and planning. Most of the patients showed at least some impairment and deficits were seen across cognitive domains. An important finding was the detrimental effect of failure on subsequent performance; having solved one problem incorrectly, patients were far more likely than controls to fail the subsequent problem. Superimposed on the general deficits, there were also specific deficits in executive tasks characteristic of frontostriatal dysfunction and deficits in mnemonic tasks characteristic of temporal lobe dysfunction. This combination of a specific form of motivational deficit, resulting in oversensitivity to negative feedback, and superimposed specific neuropsychological deficits were correlated with severity of depression. The most significant correlations were seen between mnemonic deficits and clinical rating scores. Comparisons of the deficits seen in the depressed patients in this study with other patient groups assessed with the CANTAB neuropsychological battery, showed that one of the hypotheses of the neuropsychological deficits in depression, that of "frontosubcortical' or "frontostriatal' dysfunction, was not supported. These findings are discussed in relation to the likely neural substrates of depression.

CANTAB battery: proposed utility in neurotoxicology

The CANTAB battery was developed for the assessment of cognitive deficits in humans with neurodegenerative diseases or brain damage. It consists of a series of interrelated computerized tests of memory, attention, and executive function, administered via a touch sensitive screen. It allows a decomposition of complex tasks commonly used in clinical assessment into their cognitive components and enables the extrapolation of findings from the animal literature. Tests include versions of the Wisconsin Card-Sorting Test and the Tower and London and also the Delayed Matching-to-Sample test, widely used in monkeys for visual recognition memory. The tests are constructed in such a way that they may be given to animals (monkeys) with minimal change. The nonverbal nature of the CANTAB tests makes them largely language independent and culture free. CANTAB has been standardized on a large, predominantly elderly, population and validated in neurosurgical patients as well as in patients with basal ganglia disorders, Alzheimer's disease, depression, and schizophrenia. In addition, CANTAB has been used to evaluate: a) the therapeutic effects of dopaminergic and cholinergic medication in neurodegenerative disease; b) cognition in 5-11-year-old normal, learning-disabled, and autistic children; c) deficits in patients with HIV infection; and d) early, asymptomatic Huntington's disease. The latter illustrate its usefulness in early identification of progressive disorders. It is suggested that the battery should have particular utility across a wide range of age and intelligence in longitudinal assessment after exposure to toxicants, and allow meaningful comparison with experimental studies of toxic effects in other species.

Executive functions and disease characteristics in Parkinson's disease

In the present study, we investigated the association of two executive functions with disease characteristics in Parkinson's disease (PD), especially with severity of motor symptoms. We operationalized two executive functions, viz. fluency and cognitive shifting, each in a number of tests with heterogeneous materials, but with an identical format. We calculated the correlations between test performance and disease characteristics, including the factor scores of the Unified Parkinson's Disease Rating Scale (UPDRS). The results of this study show that only cognitive shifting was consistently associated with the severity of motor symptoms in PD, in particular with rigidity. None of the fluency tests had a significant association with severity of motor symptoms. The present study indicates that PD, as reflected by the severity of motor symptoms, is not associated with a general decrease in executive function. In spite of the fact that both are executive functions and both require generation of items, fluency and cognitive shifting are differentially related to PD.

Delayed response tasks in basal ganglia lesions in man: further evidence for a striato-frontal cooperation in behavioural adaptation

To determine the respective contribution of the subcortical structures and the prefrontal cortex in behavioural adaptation, we applied the delayed response paradigm, considered as a functional marker of the dorsolateral region of the prefrontal cortex, to patients with striatal dysfunction: Parkinson's disease (n = 27), progressive supranuclear palsy (n = 20); to patients with prefrontal lesions (n = 10) and to normal control subjects (n = 24). The performance of each group was compared in four experiments: a delayed response task in which the correct answer was previously indicated by an explicit cue (externally guided task); delayed alternation and non-alternation tasks coupled with a delayed reversal task in which the patient had to discover the rule by himself in the absence of explicit cues (internally driven tasks). All groups of patients showed a short-term spatial representational memory deficit in the externally guided situation. Patients with striatal dysfunction showed difficulties in re-engaging attention on a new programme and in maintaining it. However, they did not express the spontaneous tendency to alternate nor the severe difficulties in disengaging from a previous pattern of response demonstrated by patients with prefrontal lesions. These results validate the concept of a striato-frontal functional system in humans and suggest the existence of two different levels of behavioural organization: elaboration of new programmes of behaviour in association with inhibition of previously established ones, that might be under frontal lobe control: maintenance of the new programme until the action has been accomplished and automatization for a routine utilization, that might be under control of the striatum.

Measurement of cognitive function: relating rodent performance with human minds

Rodents are the most commonly employed animals to model human cognitive dysfunction, but many of the behavioural paradigms employed for evaluation of rodent cognitive abilities measure functions rather different from those generally assessed in humans. This may be one reason for the failure of these models to allow valid predictions about drug effects in demented patients. One solution to this may be the use of a more comparative approach. Careful experimental designs indicate that comparative attentional as well as mnemonic processes can be assessed in rat and human subjects. This could be an essential step towards the successful development of drugs with therapeutic potential in cognitive disorders.

Precued shifting of attention between cognitive sets in Parkinson patients

The precueing paradigm developed by Posner has been used to examine visuospatial shifting of attention. In the current study, we modified such a paradigm so that it could be studied in nonvisuospatial domains and its component processes of disengagement, movement, and engagement could be analyzed in a similar fashion to the visuospatial domains. 14 patients with Parkinson's disease and 14 normal controls matched for age, sex, handedness, and years of education served as subjects. The speed of shifting attention was measured using the cost and benefit analysis. Analyses showed an over-all slowness in reaction time of patients with Parkinson's disease compared to the control group but without a concomitant slowness to engage, shift, and disengage their attention.

Cognitive performance in tests sensitive to frontal lobe dysfunction in the elderly depressed

The paper reports the profile of impairment across a variety of cognitive functions with special emphasis on tests sensitive to frontal lobe dysfunction, in 24 elderly depressed patients during and on recovery from mood disorder, compared with 15 age- and sex-matched controls. Traditional neuropsychological tests and a recently developed battery of computerized tests (CANTAB) were used. Impairments were found in the depressed group compared to controls and to themselves on recovery across all domains examined. The depressed group showed deficits on visuospatial recognition memory, attentional shifting at the extra-dimensional shift stage and in measures of both processing and motor speed without impaired accuracy in a visual search task. Impairments were also found on a planning task with disproportionately increased numbers of moves needed for more difficult problems and evidence of both slowed motor response and increased processing time once the task was commenced. Performance on recovery improved across all tasks. Comparisons were made with the performance of patients suffering from dementia of the Alzheimer type (DAT) and Parkinson's disease on similar tests. Response latencies in test performance were found to correlate with the number of episodes of depression suffered and with ventricular size on CT scan, as measured by computerized planimetry. On recovery, residual depression scores correlated with latency of test performance and with ventricular brain ratio. The results, thus, show that depression in the elderly is associated with a significant degree of deficit on tests sensitive to frontostriatal dysfunction. Some of the deficits appear specific to depression and some do not remit following clinical recovery. However, these impairments have to be interpreted in the context of a broad profile of cognitive deficit.

Nonverbal visual attention, but not recognition memory of learning, processes are impaired in motor neurone disease

Pathology outside the motor system is being increasingly recognised in motor neurone disease (MND) and up to 3% of patients may have overt dementia of frontal lobe type; it is not clear whether milder cognitive disturbance is a more frequent feature of the disease. Standard neuropsychological testing can be difficult in MND and we therefore used the microcomputer-controlled Cambridge Neuropsychological Test Automated Battery (CANTAB), which allows accurate assessment in the presence of motor and bulbar dysfunction. The results of subtests evaluating nonverbal visual attention, recognition memory and learning from a large (n = 50) group of patients with MND compared to normal (n = 27) and neurological disease (n = 23) control groups are presented in this report. The MND group showed significant impairment in a focal attention (visual search) task, but no deficits in memory or learning. Inspection of the visual search data showed that up to a quarter of the MND patients scored two or more standard deviations below the mean control score. It is suggested that this reflects pathology in fronto-striatal circuitry.

The alpha(2) antagonist idazoxan remediates certain attentional and executive dysfunction in patients with dementia of frontal type

Abstract The mixed alpha(1)/alpha(2) adrenoceptor agonist clonidine has been shown by us previously to impair certain attentional and executive functions in healthy volunteers. The present investigation examines the effects of the alpha(2) adrenoceptor antagonist idazoxan (IDZ) on cognitive function in patients with dementia of frontal type (DFT). Using a placebo-controlled ABBA design, three DFT patients were given two doses of IDZ and tested on a range of computerised tests of attention, memory and executive function. Idazoxan was found to produce dose-dependent improvements in performance, particularly on tests of planning, sustained attention, verbal fluency and episodic memory. In contrast, IDZ produced deficits in performance on a test of spatial working memory. These results suggest that IDZ may be useful as a putative cognitive enhancer, particularly in patients showing a specific pattern of frontal lobe dysfunction.

Card sorting performance in Parkinson's Disease: a comparison between acquisition and shifting performance

In the present study we tested the hypothesis that learned irrelevance underlies the frequently observed poor performance of Parkinson's disease (PD) patients on card sorting tests. If learned irrelevance accounts for the poor performance of PD patients on card sorting tests, PD patients and control subjects (CS) will not differ in the acquisition phase, during which basic concept formation is assessed, but they will differ in the subsequent shifting phases. We presented three distinct card sorting tests with an identical format to 51 PD patients and 24 normal controls. The groups did not differ with respect to intelligence, memory, or attention. PD patients showed a slightly better performance in the acquisition phase. In the first shifting phase, the performance of PD patients was significantly poorer than that of control subjects after correction for basic concept formation. In the second shifting phase this difference disappeared. We conclude that learned irrelevance does not account for the poor performance of PD patients in card sorting tests. The results are discussed in terms of self-generation of problem solving strategies.

Neuropsychological deficits in tests of executive function in asymptomatic and symptomatic HIV-1 seropositive men

There has been much debate about the exact nature and time of onset of the cognitive impairments associated with infection by the human immunodeficiency virus type 1 (HIV-1). Studies to date have not reached consistent conclusions. The present study comprised 22 asymptomatic and 18 symptomatic HIV-1 seropositive men, whose only risk factor for contraction of the virus was sexual intercourse, and 18 seronegative controls matched for age and IQ. Subjects were given computerized neuropsychological tests from the CANTAB battery, which assessed visuospatial memory, attention and executive function. Both the asymptomatic and the symptomatic HIV-1 seropositive subjects showed a selective pattern of deficits relative to the controls. In addition, the seropositive subjects were subtly but significantly impaired on tests of executive function but unimpaired on certain tests of visual memory. This finding supports an hypothesis that frontostriatal dysfunction occurs in HIV-1 infected individuals prior even to the expression of clinical symptoms.

Concept generation: validation of a test of executive functioning in a normal aging population

A new test, Concept Generation, was designed to fractionate the processes that underlie sorting performance in an efficient paper-and-pencil format. The test was administered to 60 subjects, aged 18-79. Results indicated age-related deficits for self-initiated concept formation, shifting set, output monitoring, and perseverative tendencies. When cuing was introduced to increase structure, age group differences were attenuated or eliminated. Within the older group, subgroups were identified based upon the nature of their repetitions. The hypothesis that sorting behavior is mediated by executive functions led to correlational analyses between Concept Generation scores and other measures of executive functioning. The pattern of correlations supported the construct validity of the Concept Generation test. In addition to providing preliminary evidence for the usefulness of Concept Generation in executive functioning assessment, the results replicated and extended previous work on executive functioning in older individuals.

Cognitive deficits precede motor deficits in a slowly progressing model of parkinsonism in the monkey

Five adult Macaca fascicularis monkeys were trained to perform tests of cognitive and motor functioning that included a complex visual pattern discrimination task, an object retrieval task, a test of task persistence, and a timed motor task. Once stable baseline performance was achieved, monkeys were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at doses of 0.05 to 0.075 mg/kg, 2 to 3 times per week for a total of 24 weeks. Animals were assessed weekly for performance on the previously learned tasks. All monkeys developed performance deficits in a predictable pattern with behavioural and cognitive deficits (i.e. deficits in task persistence and the cognitive component of object retrieval) appearing in advance of measurable motor deficits. Deficits in visual pattern discrimination never appeared. These results show that specific cognitive dysfunction pre-dates motor dysfunction in a chronic, slowly progressing parkinson model in monkeys and support the contention that cognitive deficits in Parkinson's disease may precede the motor signs of the disorder and may not be caused by them.

Clonidine and diazepam have differential effects on tests of attention and learning

The noradrenergic system has repeatedly been implicated in the mediation of attentional processes. Using a double-blind, placebo-controlled design, the present investigation examines the effects of two doses (1.5 micrograms/kg and 2.5 micrograms/kg) of the alpha 2 adrenoceptor agonist clonidine (CLO) on performance of various computerised tests of attention and learning in healthy, young volunteers. These are compared to the effects produced by two doses (5 mg and 10 mg) of diazepam (DZP) on largely the same set of neuropsychological tests in a comparable set of subjects. Both doses of CLO were found to impair performance of the RVIP test of sustained attention, while the higher dose alone improved visuo-spatial learning. Conversely, the higher dose of DZP produced profound deficits on visuo-spatial learning, and impaired attentional set-shifting. This study suggests a role for the alpha 2 adrenoceptor in selective attention, and for the benzodiazepine receptor in specific cognitive processes mediated by discrete cortical regions.

Neuropsychological evidence for frontostriatal dysfunction in schizophrenia

Schizophrenics and controls were compared on a computerized test of attentional set-shifting which provides a componential analysis of the Wisconsin Card Sort Test and has previously been shown to be sensitive to frontal lobe dysfunction and Parkinson's disease. The main test was of extra-dimensional shifting where subjects are required to shift response to an alternative perceptual dimension. In one condition, termed 'perseveration', subjects are required to shift to a novel dimension and ignore the previously relevant one. In the other condition, termed 'learned irrelevance', subjects are required to shift to the previously irrelevant dimension and ignore a novel one. Chronic medicated schizophrenics (N = 32) show a highly significant impairment on the perseveration but not the learned irrelevance condition, as compared to normal age and IQ matched controls (N = 24). This was true even of a subgroup of patients with preserved IQ. The impairments in attentional set-shifting failed to correlate with patients' scores on the Mini-Mental State Examination (mean; S.D. 26.8; 1.8) or with scores on a test of recognition memory. These results provide evidence for a specific deficit in a set-shifting test of executive function and support a hypothesis of frontostriatal dysfunction in schizophrenia.

Comparison of executive and visuospatial memory function in Huntington's disease and dementia of Alzheimer type matched for degree of dementia

Groups of patients with Hungington's disease and probable dementia of Alzheimer type (DAT) matched for level of dementia on the basis of mini mental state examination scores were compared in several tests of visual memory and tests sensitive to frontal lobe dysfunction. Whereas recall of patients with DAT tended to be worse on the Kendrick object learning test, the two groups were equivalent on tests of sensorimotor ability and delayed matching to sample performance. By contrast, the patients with Huntington's disease were significantly worse on tests of pattern and spatial recognition, simultaneous matching to sample, visuospatial paired associates, and on three tests sensitive to frontal lobe dysfunction--namely, the Tower of London test of planning, spatial working memory, and a visual discrimination learning and reversal paradigm. The impairments in these tests, however, did not always qualitatively resemble those seen in patients with frontal lobe damage and may be more characteristic of primary neostriatal deficit. In the visual discrimination paradigm the patients with Hungtington's disease were significantly worse than the patients with DAT at the simple reversal stage, where they displayed significant preservation to the previously rewarded alternative. The results are consistent with the hypothesis that patients with Huntington's disease exhibit deficits in tests sensitive to frontostriatal dysfunction and that this form of intellectual deterioration is qualitatively distinct from that seen in Alzheimer's disease.

The effect of task complexity on reaction times in memory scanning and visual discrimination in Parkinson's disease

Within the context of the bradyphrenia debate, two experiments designed to measure the cognitive speed of Parkinson patients (PD) were conducted with 58 subjects. The experiments took the form of a high-speed memory scanning task using memory sets consisting of one-six words or one-six abstract figures. In a visual discrimination task, two simultaneously presented abstract images had to be compared, the complexity of the images being varied through four stages. Motor response was constant, reaction time was the dependent variable. PD differed from matched controls in the level (significant only in scanning) but in neither experiment in the slope of reaction time curves. Interaction group x complexity (MANOVA) was not significant. Correlations between disease parameters and a 'complexity effect' measure were low throughout. However, the link to general intelligence was significant. The findings contradict the conventional bradyphrenia hypothesis.

Improving the Clinical Recognition of Very Mild Dementia Using Multiple Levels of Assessment

Neuropsychological test batteries alone are often unable to differentiate very mild dementia from both normal aging and mild dementia of the Alzheimer type (DAT). The authors hypothesized that some of the difficulties of neuropsychological tests in the identification of very mild dementia could be overcome by the inclusion of additional levels of assessment (activities of daily living, psychopathology, and subjective complaints). Three groups (very mild dementia, mild-to-moderate DAT, and healthy control subjects) of community-dwelling older persons were assessed on cognitive and noncognitive variables. Results indicated that noncognitive variables improved prediction of group assignment. For accurate identification of all patients with very mild dementia, in addition to neuropsychological variables, subjective complaints of impaired orientation and disturbances of apperception were necessary and sufficient.

Visuo-spatial short-term recognition memory and learning after temporal lobe excisions, frontal lobe excisions or amygdalo-hippocampectomy in man

Three groups of neurosurgical patients with temporal lobe excisions, frontal lobe excisions or unilateral amygdalo-hippocampectomy were assessed on a computerized battery of tasks designed to investigate visuo-spatial short-term recognition memory and learning. A double dissociation is reported between deficits of pattern recognition memory and spatial recognition memory which were observed in the two posterior groups and frontal lobe patients, respectively. In addition, both the temporal lobe and amygdalo-hippocampectomy patients were also impaired on a delayed matching-to-sample paradigm whilst frontal lobe patients performed at an equivalent level to controls. Finally, whilst the impaired performance of the three groups was indistinguishable on a test of paired-associate learning, quite different patterns of deficit were observed on a test of spatial working memory. These results are discussed with reference to recent suggestions that visual recognition memory is mediated by a neural system which includes, as major components, the inferotemporal cortex, the medial temporal lobe structures and particular sectors of the frontal lobe, and are compared to previous findings from patients with idiopathic Parkinson's disease and dementia of the Alzheimer type.

Parkinsonian patients without dementia or depression do not suffer from bradyphrenia as indexed by performance in mental rotation tasks with and without advance information

A predominant symptom of Parkinson's disease is akinesia and bradykinesia, slowing in the initiation and execution of voluntary movement. There has long been speculation as to whether cognitive processes undergo similar processes, but findings may be confounded by the frequent co-occurrence of dementia and/or depression. Mental rotation provides an internal or cognitive analogue of real movement, and enables us to determine the speed of such mental processes independent of any concurrent motor slowing in response initiation and execution. Medicated patients with Parkinson's disease who were free of dementia and depression were found to be able to mentally rotate alphanumeric or figural stimuli, with and without advance information as to the view (front or back) of a stick figure shortly to be shown, as rapidly as normal healthy controls. We conclude that cognitive processes involved in mental rotation are not necessarily slowed in Parkinson's disease.

Auditory selective attention is impaired in Parkinson's disease--event-related evidence from EEG potentials

Selective attention refers to the ability to focus on one channel of information in the presence of distracting other channels. For the visual modality, results on impairments of selective attention have been conflicting in patients with idiopathic Parkinson's disease (PD). Independent of possible interferences from visual or movement disturbances selective attention can be measured as the so-called 'processing negativity' (PN) using auditory evoked potentials. Therefore, auditory selective attention with the PN was measured in 14 patients with PD and 16 control subjects. Subjects had to attend to tones presented to one ear (i.e. to press a button to occasionally presented longer tones) and ignore tones presented to the other ear. Tones were presented at a rate of 1/s ('slow') or 2/s ('fast'). PN was measured as the difference of the potentials evoked by attended minus ignored standard tones. PN was significantly smaller in the PD patients than in the controls with slow presentation. There was no difference between both groups with fast presentation. PN remained unchanged when patients had a 12-h withdrawal of their usual anti-Parkinsonian drug therapy. PD patients and controls did not differ in their P3 component evoked in the usual 'oddball' task nor in the mismatch negativity evoked by the occasionally longer tones in the PN task. The results provide evidence for an impairment of auditory selective attention that is specific for patients with PD (i.e. independent of the P3 component).

The pedunculopontine tegmental nucleus: a role in cognitive processes?

The cholinergic pedunculopontine tegmental nucleus, located in the brainstem and part of the reticular formation, has been traditionally linked to motor function, arousal and sleep. Its anatomical connections, however, raise the possibility that the pedunculopontine tegmental nucleus is also involved in other aspects of behaviour such as motivation, attention and mnemonic processes. This is of obvious importance, since the pedunculopontine tegmental nucleus undergoes degeneration in human neurodegenerative disorders also characterized by attentional and/or mnemonic deficits. Moreover, recent behavioural animal work suggests that cognitive processes may be represented in the pedunculopontine tegmental nucleus. The difficulty that faces research in this area, however is the possible influence of cognition by other processes, such as arousal state, motivation and motor function. Nevertheless, by reviewing the literature, the pedunculopontine tegmental nucleus seems to be involved in attentional and possibly also in learning processes. These processes could be mediated by influencing cortical function via the thalamus, basal forebrain and basal ganglia. The involvement of the pedunculopontine tegmental nucleus in mechanisms of memory, however, seems to be rather unlikely.

Lexical decision in Parkinson disease: lack of evidence for generalized bradyphrenia

Twenty-two nondemented patients with idiopathic Parkinson disease (PD) and 22 controls completed a lexical decision task for which the expected relationship between primes and targets was manipulated. Both reaction times and movement times were measured. PD subjects were as effective as controls in utilizing the priming cues to reduce their reaction times compared with a neutral condition. This facilitation occurred even at the shortest stimulus onset asynchrony employed (300 ms), and was observed in a condition requiring a shift of attention, suggesting that PD patients experience no general cognitive slowing and no difficulty efficiently shifting attention to a specified semantic category. The degree of facilitation was significantly greater in the PD group in several comparisons, indicating hyperpriming. Finally, expectancy primes facilitated movement times in the PD group only. Although the results do not support the existence of generalized bradyphrenia in nondemented Parkinson disease, the hyperpriming effect and correlational analyses involving vocabulary scores and choice reaction time do raise the possibility of a subtle semantic processing deficit or an impairment of strategic decision-making in PD.

Impaired problem solving in Parkinson's disease: impact of a set-shifting deficit

Parkinson's disease (PD) is associated with specific cognitive deficits in the absence of dementia, including the inability to suppress previously learned responses in a changed context. Our goal was to determine whether this set-shifting deficit is sufficient to account for impaired performance on a problem-solving task, or, instead, whether it is necessary to postulate deficits in one or more other cognitive capacities, such as logical deduction. Deductive reasoning and other conceptual abilities were assessed in 15 nondemented subjects with PD who had never been medicated, 15 nondemented subjects with PD who were currently receiving medication, and 15 healthy elderly control subjects. On a deductive reasoning task, Poisoned Food Problems, the PD groups made more errors than the control group. The PD groups' error pattern was characterized by intrusions of information from previous problems. By contrast, the PD groups made appropriate assessments of redundant and irrelevant information that appeared in these problems, and performed normally on other tests of concept formation and problem solving that did not require set shifting, indicating that the capacities for logical deduction and concept formation were intact. The set-shifting deficit, conceptualized as a difficulty in suppressing a prepotent response, appears to be a primary cognitive impairment in PD and presumably arises from dysfunction of the nigrostriatal-dorsolateral prefrontal cortex complex loop.

Evidence for executive dysfunction in autism

A group of young people with autism (ranging in ability from high functioning to moderately learning disabled), and ability-matched control groups of (i) non-autistic individuals with moderate learning disabilities, and (ii) normally developing children, were presented with two tests of executive function: the Intra-dimensional/Extra-dimensional set-shifting task and the Tower of London planning task. These tests were graded in difficulty and included internal control measures. On each task, the autistic group was differentially impaired with respect to both control groups. Moreover, this impairment was specific to the stages of each task which placed greatest demands upon executive control. This evidence for executive dysfunction in autism is discussed in the context of Norman and Shallice's (Centre for Human Information Processing Technical Report 99, 1980) "Supervisory Attentional System" model of frontal function.

Cognitive deficits in progressive supranuclear palsy, Parkinson's disease, and multiple system atrophy in tests sensitive to frontal lobe dysfunction

Groups of patients with idiopathic Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy or Steele-Richardson-Olszewski syndrome, matched for overall clinical disability, were compared using three computerised cognitive tests previously shown to be sensitive to frontal lobe dysfunction. On a test of planning based on the Tower of London task, all three groups were impaired, but in different ways. The groups with palsy and Parkinson's disease were slower in the measure of initial thinking time, whereas the group with multiple system atrophy was only slower in a measure of thinking time subsequent to the first move, resembling patients with frontal lobe damage. On a test of spatial working memory, each group showed deficits relative to their matched control groups, but the three groups differed in their strategy for dealing with this task. On a test of attentional set shifting, each group was again impaired, mainly at the extradimensional shifting stage, but the group with Steele-Richardson-Olszewski syndrome exhibited the greatest deficit. The results are compared with previous findings in patients with Alzheimer's disease or frontal lobe damage. It is concluded that these basal ganglia disorders share a distinctive pattern of cognitive deficits on tests of frontal lobe dysfunction, but there are differences in the exact nature of the impairments, in comparison not only with frontal lobe damage but also with one another.