Memory and learning strategies in patients with Parkinson's disease

Comparison of core and process scores on the California Verbal Learning Test-3 for Parkinson's disease and essential tremor patients

INTRODUCTION

Parkinson's disease (PD) and essential tremor (ET) are two disorders known to lead to executive dysfunction, presumably through distinct pathways to the frontal lobes via the striatum or cerebellum, respectively. Memory functioning in PD and ET patients has been previously suggested to be adversely impacted by executive dysfunction. The aims of this exploratory study were to compare memory performance between and within groups on the California Verbal Learning Test - 3 (CVLT-3) through the analysis of core and process scores and to understand the relationship of these scores with measures of executive functioning.

METHOD

Seventy PD and 54 ET patients completed comprehensive neuropsychological testing. Independent sample t-tests or Mann-Whitney tests were used to compare between group core and process scores on the CVLT-3. Within-subjects analyses were conducted via Wilcoxon Signed Rank Test due to nonparametric data. Spearman's correlations were conducted to explore the relationship between memory process scores and measures of executive functioning.

RESULTS

The ET and PD samples were similar with regard to age, education, gender, and general cognitive functioning. PD patients made more repetition errors (U = 2391.50, p = .01) than ET patients and Normal Memory PD patients made more repetition errors than Low Memory PD patients (U= 711.00, p= .00). Correlational analyses revealed repetition errors were negatively associated with tests of inhibition, set shifting, and working memory (rs = -.293, -.232). ET patients demonstrated a preference for a serial cluster learning strategy (T = 861.00, p = .005), similar to PD patients (T= 1633.00, p = <.001).

CONCLUSIONS

The study revealed presence of higher repetition errors in the PD sample that was demonstrated to have a negative relationship with measures of executive functioning. Implications for investigating process ("qualitative") scores in memory performance to determine extent of executive involvement are discussed.

Verbal Learning Impairment in Parkinson's Disease: Role of the Frontostriatal System in Working and Strategic Memory

INTRODUCTION

Learning is a long-term memory process, influenced by working memory control processes, including recognition of semantic properties of items by which subjects generate a semantic structure of engrams. The aim of the study was to investigate the verbal learning strategies of individuals with Parkinson's disease (PD).

METHODS

Thirty individuals with idiopathic PD and healthy control (HC) subjects were tested with a multi-trial word list learning, under two conditions: without cue and then with an explicit cue suggesting the categories in the list, respectively.

RESULTS

In comparison to HC subjects, individuals with PD recalled fewer words and achieved a reduced number of categorical clusters; the strategical cue did not improve their performance.

CONCLUSION

This suggests, besides a difficulty in identifying the correct learning strategy, a deficit in working memory, which undermines the strategy implementation.

Profile of cognitive impairment in late-stage Parkinson's disease

INTRODUCTION

The profile of cognitive impairment associated with the late stages of Parkinson's disease (LSPD) is rarely reported. Its characterization is necessary to better understand the cognitive changes that occur as the disease progresses and to better contribute to its management.

METHODS

In this cross-sectional study, we characterized the cognitive profile of LSPD patients using the comprehensive assessment methodology proposed by the International Parkinson and Movement Disorders Society Task Force. The association of clinical and demographic variables with dementia diagnosis was also investigated using binary logistic regression analysis.

RESULTS

Eighty-four LSPD patients were included (age 75.4 ± 6.9; disease duration 16.9 ± 7.5). Fifty-four (64.3%) were classified as demented and presented a global impairment cognitive profile. In the nondemented group (N = 30), 25 (83.3%) LSPD patients met the diagnostic criteria for mild cognitive impairment, mostly with multiple domain impairment (96.0%) and a heterogeneous profile. Memory was the most frequent and severely impaired cognitive domain in both groups. Disease disability, orientation, complex order comprehension, verbal learning, and visuoconstructive abilities were significantly associated with dementia diagnosis (p < .05).

CONCLUSIONS

Cognitive impairment in multiple domains was common in LSPD patients. The most frequent and prominent deficits were in the memory domain, with a strong interference from attention impairment. Disease disability, orientation, complex order comprehension, verbal learning, and visuoconstructive abilities proved to be important determinants for dementia diagnosis.

Role of dopamine and clinical heterogeneity in cognitive dysfunction in Parkinson's disease

Parkinson's disease (PD) is commonly treated with dopaminergic medication, which enhances some, while impairing other cognitive functions. It can even contribute to impulse control disorder and addiction. We describe the history of research supporting the dopamine overdose hypothesis, which accounts for the large within-patient variability in dopaminergic medication effects across different tasks by referring to the spatially non-uniform pattern of dopamine depletion in dorsal versus ventral striatum. However, there is tremendous variability in dopaminergic medication effects not just within patients across distinct tasks, but also across different patients. In the second part of this chapter we review recent studies addressing the large individual variability in the negative side effects of dopaminergic medication on functions that implicate dopamine, such as value-based learning and choice. These studies begin to unravel the mechanisms of dopamine overdosing, thus revising the strict version of the overdose hypothesis. For example, the work shows that the canonical boosting of reward-versus punishment-based choice by medication is greater in patients with depression and a non-tremor phenotype, which both implicate, among other pathology, more rather than less severe dysregulation of the mesolimbic dopamine system. Future longitudinal cohort studies are needed to identify how to optimally combine different clinical, personality, cognitive, neural, genetic and molecular predictors of detrimental medication effects in order to account for as much of the relevant variability as possible. This will provide a useful tool for precision neurology, allowing individual and contextual tailoring of (the dose of) dopaminergic medication in order to maximize its cognitive benefits, yet minimize its side effects.

Feasibility and Acceptability of Computerised Cognitive Training of Everyday Cognition in Parkinson's Disease

Objectives

We piloted a computerised cognitive training battery in a group of participants with Parkinson's disease without dementia to investigate the relevance of the training to daily life and the feasibility and the acceptability of the tasks. Previous studies of CT have had limited success in the benefits of training, extending to improvements in everyday function. By taking a pragmatic approach and targeting training to the cognitive skills affected by Parkinson's disease (planning, attention, and recollection), whilst using tasks that emulated real-life scenarios, we sought to understand whether participants perceived the training to be effective and to identify the elements of the training that elicited beneficial effects.

Methods

Four participants completed a cognitive training session comprising three distinct tasks 5 days a week over two weeks. Participants completed baseline questionnaires examining health-related quality of life, everyday cognition, and apathy before the training period, after the last session, and two weeks after the last session. An interview was held after participants had completed the training.

Results

The findings indicated that participants felt the training was acceptable, enhanced their awareness, and encouraged them to monitor their thinking abilities. The group interview indicated that the training was feasible; participants felt the tasks had potential to improve everyday performance, but more supporting information should be provided to facilitate this transfer. Responses to the questionnaires reflected these findings, indicating improvement for some participants' cognition and quality of life. Objective measures supported the subjective reports; there were improvements in some but not all domains. Performance on the planning and recollection tasks improved over the training period, and the evidence for improvement on the attention task was mixed.

Conclusion

This study has found that pragmatic computer-based training with real-life outcomes is both feasible and acceptable and should be evaluated more extensively using controlled methods.

Improving Prospective Memory in Persons With Parkinson Disease: A Randomized Controlled Trial

BACKGROUND

Prospective memory (PM) is essential for productive and independent living and necessary for compliance with prescribed health behaviors. Parkinson disease (PD) can cause PM deficits that are associated with activity limitations and reduced quality of life. Forming implementation intentions (IIs) is an encoding strategy that may improve PM in this population.

OBJECTIVE

To determine the effect of IIs on PM performance in PD.

METHODS

This was a laboratory-based randomized controlled trial. Participants with mild to moderate PD without dementia (n = 62) performed a computerized PM test (Virtual Week) under standard instructions. One week later they were randomly allocated to perform it again while using either IIs or a rehearsal (RR) encoding strategy.

RESULTS

PM performance was better with the use of both strategies relative to standard instructions. This effect was larger for tasks with event-based compared with time-based cues. In addition, IIs resulted in a larger effect than RR for the nonrepeated tasks.

CONCLUSIONS

Strategies that support full encoding of PM cues and actions can improve PM performance among people with PD, particularly for tasks with cues that are readily available in the environment. IIs may be more effective than RR for nonrepeated tasks, but this finding warrants verification. Future work should address transfer of strategy use from the laboratory to everyday life. Targeted strategies to manage PM impairment could improve function and quality of life and significantly affect clinical care for people with PD.

Memory Similarities Between Essential Tremor and Parkinson's Disease: A Final Common Pathway?

OBJECTIVE

A growing body of literature supports the view that essential tremor (ET) involves alteration of cerebellar-thalamo-cortical networks which can result in working memory and executive deficits. In this study, we tested the hypothesis that individuals with ET would exhibit worse performance on memory tasks requiring more intrinsic organization and structuring (i.e., word lists) relative to those with fewer 'executive' demands (i.e., stories), similar to that previously observed in individuals with Parkinson's disease (PD).

METHOD

Participants included a convenience sample of 68 ET patients and 68 idiopathic PD patients, retrospectively matched based on age, education, and sex. All patients underwent routine neuropsychological evaluation assessing recent memory, auditory attention/working memory, language, and executive function. Memory measures included the Hopkins Verbal Learning Test-R and WMS-III Logical Memory.

RESULTS

Both ET and PD patients performed significantly worse on word list than story memory recall tasks. The magnitude of the difference between these two memory tasks was similar for ET and PD patients. In both patient groups, performance on measures of executive function and auditory attention/working memory was not distinctly correlated with word list vs. story recall.

CONCLUSIONS

These findings suggest that frontal-executive dysfunction in both ET and PD may negatively influence performance on memory tests that are not inherently organized. Although the pathophysiology of these two 'movement disorders' are quite distinct, both have downstream effects on thalamo-frontal circuitry which may provide a common pathway for a similar memory phenotype. Findings are discussed in terms of neuroimaging evidence, conceptual models, and best practice.

Prospective memory in Parkinson disease during a virtual week: effects of both prospective and retrospective demands

OBJECTIVE

This study investigated the effect of Parkinson's disease (PD) on event-based prospective memory tasks with varying demand on (1) the amount of strategic attentional monitoring required for intention retrieval (prospective component), and (2) the retrospective memory processes required to remember the contents of the intention or the entire constellation of prospective memory tasks.

METHOD

Twenty-four older adults with PD and 28 healthy older adults performed the computerized Virtual Week task, a multi-intention prospective memory paradigm that simulates everyday prospective memory tasks. The Virtual Week included regular (low retrospective memory demand) and irregular (high retrospective memory demand) prospective memory tasks with cues that were focal (low strategic monitoring demand) or less focal (high strategic monitoring demand) to the ongoing activity.

RESULTS

For the regular prospective memory tasks, PD participants were impaired when the prospective memory cues were less focal. For the irregular prospective memory tasks, PD participants were impaired regardless of prospective memory cue type. PD participants also had impaired retrospective memory for irregular tasks, which was associated with worse prospective memory for these tasks during the Virtual Week.

CONCLUSIONS

When retrospective memory demands are minimized, prospective memory in PD can be supported by cues that reduce the executive control demands of intention retrieval. However, PD-related deficits in self-initiated encoding or planning processes have strong negative effects on the performance of prospective memory tasks, with increased retrospective memory demand.

Autobiographical memory in Parkinson's disease: a retrieval deficit

This study examined the effects of providing cues to facilitate autobiographical memory retrieval in Parkinson's disease. Previous findings have shown that individuals with Parkinson's disease retrieve fewer specific autobiographical memories than older adult controls. These findings are clinically significant since the quality of autobiographical memory is linked to identity and sense of self. In the current study, 16 older adults with Parkinson's disease without dementia and 16 matched older adult controls were given 3 min in which to recall autobiographical memories associated with five different time periods and to give each memory a short title. Participants were later asked to retrieve the memories in three phases: firstly in a free recall phase; secondly in response to general cues (time periods) and finally in response to specific cues (the short titles previously given). The number of memories and the quality of the memory (general or specific) was recorded in each condition. Compared with matched older adult controls, the Parkinson's disease group was impaired in retrieving the memories that they had previously given in the free recall phase and in response to general cues. The performance of the group with Parkinson's disease was only equivalent to the older adults when they retrieved memories in response to self-generated cues. The findings are discussed in relation to theories of autobiographical memory and the neuropsychology of Parkinson's disease.

Association between subcortical volumes and verbal memory in unmedicated depressed patients and healthy controls

Research has shown poor performance on verbal memory tasks in patients with major depressive disorder relative to healthy controls, as well as structural abnormalities in the subcortical structures that form the limbic-cortical-striatal-pallidal-thalamic circuitry. Few studies, however, have attempted to link the impairments in learning and memory in depression with these structural abnormalities, and of those which have done so, most have included patients medicated with psychotropic agents likely to influence cognitive performance. This study thus examines the relationship between subcortical structural abnormalities and verbal memory using the California Verbal Learning Test (CVLT) in unmedicated depressed patients. A T1 weighted magnetic resonance imaging scan and the CVLT were obtained on 45 subjects with major depressive disorder and 44 healthy controls. Using the FMRIB's Integrated Registration and Segmentation Tool (FIRST) volumes of selected subcortical structures were segmented and correlated with CVLT performance. Depressed participants showed significantly smaller right thalamus and right hippocampus volumes than healthy controls. Depressed participants also showed impaired performance on global verbal learning ability, and appeared to depend upon an inferior memory strategy (serial clustering). Measures of serial clustering were correlated significantly with right hippocampal volumes in depressed participants. Our findings indicate that depressed participants and healthy controls differ in the memory strategies they employ, and that while depressed participants had a smaller hippocampal volume, there was a positive correlation between volume and use of an inferior memory strategy. This suggests that larger hippocampal volume is related to better memory recall in depression, but specifically with regard to utilizing an inferior memory strategy.

Altered implicit category learning in anorexia nervosa

OBJECTIVE

Recent research has identified specific cognitive deficits in patients with anorexia nervosa (AN), including impairment in executive functioning and attention. Another such cognitive process, implicit category learning has been less studied in AN. This study examined whether implicit category learning is impaired in AN.

METHOD

Twenty-one women diagnosed with AN and 19 control women (CW) were administered an implicit category learning task in which they were asked to categorize simple perceptual stimuli (Gabor patches) into one of two categories. Category membership was based on a linear integration (i.e., an implicit task) of two stimulus dimensions (orientation and spatial frequency of the stimulus).

RESULTS

AN individuals were less accurate on implicit category learning relative to age-matched CW. Model-based analyses indicated that, even when AN individuals used the appropriate (i.e., implicit) strategy they were still impaired relative to CW who also used the same strategy. In addition, task performance in AN patients was worse the higher they were in self-reported novelty seeking and the lower they were in sensitivity to punishment.

CONCLUSIONS

These results indicate that AN patients have implicit category learning deficits, and given this type of learning is thought to be mediated by striatal dopamine pathways, AN patients may have deficits in these neural systems. The finding of significant correlations with novelty seeking and sensitivity to punishment suggests that feedback sensitivity is related to implicit learning in AN.

A differential deficit in time- versus event-based prospective memory in Parkinson's disease

OBJECTIVE

The aim of the current study was to clarify the nature and extent of impairment in time- versus event-based prospective memory in Parkinson's disease (PD). Prospective memory is thought to involve cognitive processes that are mediated by prefrontal systems and are executive in nature. Given that individuals with PD frequently show executive dysfunction, it is important to determine whether these individuals may have deficits in prospective memory that could impact daily functions, such as taking medications. Although it has been reported that individuals with PD evidence impairment in prospective memory, it is still unclear whether they show a greater deficit for time- versus event-based cues.

METHOD

Fifty-four individuals with PD and 34 demographically similar healthy adults were administered a standardized measure of prospective memory that allows for a direct comparison of time-based and event-based cues. In addition, participants were administered a series of standardized measures of retrospective memory and executive functions.

RESULTS

Individuals with PD demonstrated impaired prospective memory performance compared to the healthy adults, with a greater impairment demonstrated for the time-based tasks. Time-based prospective memory performance was moderately correlated with measures of executive functioning, but only the Stroop Neuropsychological Screening Test emerged as a unique predictor in a linear regression.

CONCLUSIONS

Findings are interpreted within the context of McDaniel and Einstein's (2000) multiprocess theory to suggest that individuals with PD experience particular difficulty executing a future intention when the cue to execute the prescribed intention requires higher levels of executive control.

Strategy instruction in Parkinson's disease: influence on cognitive performance

OBJECTIVES

Though strategic deficits are extensively investigated in Parkinson's disease (PD), little is known about the effects of instruction for PD patients. Thus, we compared the ability to internally generate a cognitive strategy with the ability to use a strategy after elaborate strategy instruction.

METHODS

Patients with PD (n=14) and matched healthy controls (n=22) were administered a Numerosity Judgement task in which they had to determine different numerosities of blocks presented in a square grid. In more complex task configurations, healthy participants tend to use a subtraction strategy. Participants in our study were confronted with a counting condition (A), a strategy initiation condition without instruction (B), and a strategy elaboration and strategy training condition (C).

RESULTS

Patients and controls were comparable with respect to basic cognitive measures. PD patients and controls performed equivalently within the counting condition (A), but patients needed significantly more trials to initiate the subtraction strategy. With the exception of 1 PD patient, all patients were able to internally initiate the strategy (condition B). In condition C, both groups increased reaction times, but patients were significantly slower than controls. Moreover, only patients significantly increased error rates after strategy instruction.

CONCLUSION

As long as sufficient time is provided for solving the task, results do not show a general deficit in the ability to internally generate a cognitive strategy in PD. Failures in strategy utilization strongly depend on cognitive load (working memory, executive functions). This bears important implications for the neuropsychological rehabilitation of PD patients.

Overgeneral autobiographical memory in Parkinson's disease

Autobiographical memory (AM) concerns the ability to remember past events from one's own life and consists of autobiographical knowledge (personal facts) and autobiographical incidents (personal events). The novelty of this research was to assess both personal factual and personal event AM in Parkinson's disease (PD) for specified lifetime periods. An autobiographical fluency task was used in which participants were asked to recall personal events and personal facts from five separate lifetime periods. Previous findings as well the brain regions affected in PD lead to the hypothesis that Parkinson's patients would recall less autobiographical memories especially for the most recent lifetime periods. Sixteen non-demented and non-depressed Parkinson's patients and sixteen age-education-matched controls participated. The results showed a temporal gradient for the recall of personal events in Parkinson's patients as they recalled fewer events for recent time periods. The PD group also had more difficulties in recalling autobiographical events rather than an autobiographical knowledge. The difficulty in recalling autobiographical events was characterized by overgenerality, with PD patients failing to generate specific episodic memories.

Retrieval processes in adults with ADHD: a RAVLT study

Attention-deficit hyperactivity disorder (ADHD) is associated with memory deficiencies. In the current study we compared different aspects of verbal memory using standard and constructed measures of the Rey auditory verbal learning test (RAVLT). Performance on learning and recognition measures of RAVLT was similar in both ADHD and control groups. In contrast, adults with ADHD committed more double recalls and intrusion errors, indicating inaccurate recall processes. These findings suggest that memory problems in adults with ADHD may be caused by deficient executive processes that support retrieval from memory.

HIV-associated prospective memory impairment increases risk of dependence in everyday functioning

HIV infection is associated with impairments in prospective memory (ProM), an aspect of episodic memory that refers to the ability to execute a future intention, such as remembering to take a medication at a specific time. The current study sought to examine the relationship between HIV-associated ProM impairment and the successful management of instrumental activities of daily living (IADLs). In a cohort of 66 HIV-infected individuals, ProM accounted for a significant proportion of variance in self-reported IADL dependence, over and above that which was explained by retrospective memory and by current affective distress. Analysis of component cognitive processes revealed that the relationship between HIV-associated ProM deficits and IADL dependence was driven by impaired cue detection and by deficits in self-initiated intention retrieval. Results were not better explained by demographic factors, HIV disease severity, psychiatric comorbidity, or substance use. Collectively, these data support the potential incremental ecological validity of ProM as a predictor of dependence in IADLs among persons living with HIV infection.

Spatial deficits in a mouse model of Parkinson disease

RATIONALE

Accumulating evidence in humans demonstrated that visuo-spatial deficits are the most consistently reported cognitive abnormalities in Parkinson disease (PD). These deficits have been generally attributed to cortical dopamine degeneration. However, more recent evidence suggests that dopamine loss in the striatum is responsible for the visuo-spatial abnormalities in PD. Studies based on animal models of PD did not specifically address this question.

OBJECTIVES

Thus, the first goal of this study was to analyze the role of dopamine within the dorsal striatum in spatial memory. We tested bilateral 6-OHDA striatal lesioned CD1 mice in an object-place association spatial task. Furthermore, to see whether the effects were selective for spatial information, we measured how the 6-OHDA-lesioned animals responded to a non-spatial change and learned in the one-trial inhibitory avoidance task.

RESULTS

The results demonstrated that bilateral (approximately 75%) dopamine depletion of the striatum impaired spatial change discrimination. On the contrary, no effect of the lesion was observed on non-spatial novelty detection or on passive avoidance learning.

CONCLUSIONS

These results confirm that dopamine depletion is accompanied by cognitive deficits and demonstrate that striatal dopamine dysfunction is sufficient to induce spatial information processing deficits.

Striatal dopamine transporters correlate with simple reaction time in elderly subjects

The decline in motor performance that accompanies advanced age has unclear neurobiological substrates but may relate, in part, to degeneration of the nigrostriatal dopamine system. This research tested the hypothesis that striatal dopamine transporter (DAT) availability in healthy elderly individuals was related to measures of motor performance. Thirty-six healthy volunteers (18 male, 18 female) who ranged in age from 68 to 88 (75.4+/-4.9 years) received a neuropsychological evaluation that included two primary motor measures (tested with dominant hand): (1) simple reaction time (SRT); and (2) finger tapping (FT). Subjects underwent SPECT scanning with [(123)I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ([(123)I]beta-CIT) for measurement of striatal DAT availability. A ratio of specific to nondisplaceable brain uptake (i.e., radical V3 =[striatal-occipital]/occipital), a measure proportional to the binding potential (B(max)/K(D)), was derived. SRT was significantly correlated with striatal DAT availability with or without controlling for the contribution of age. However, contrary to hypothesis, FT was not correlated with striatal DAT availability. Comparison measures, including episodic memory and general intelligence, were also unrelated to striatal DAT availability. These results demonstrate that a loss of nigrostriatal dopaminergic function likely contributes to slowing of reaction speed with advancing age.

Explicit category learning in Parkinson's disease: deficits related to impaired rule generation and selection processes

The present study examined the source of explicit category learning deficits previously noted in patients with Parkinson's disease (PD). Task stimuli consisted of 4 binary-valued cues that together determined category assignment, although some cues were more important for the categorization decision. Participants verbalized the hypotheses being tested to provide several measures of the hypothesis testing. Analyses of these verbal protocols indicated that PD patients were impaired on rule generation and selection but not rule shifting. Patients had particular difficulty noting the relative importance of the cues. Specific aspects of performance were differently correlated with neuropsychological measures of working memory and hypothesis testing ability. Together, the results suggest that the cognitive processes required for explicit category learning are mediated by partially distinct neural mechanisms.

Metamemory experiments in neurological populations: a review

Metamemory refers to knowledge about one's memory capabilities and strategies that can aid memory, as well as the processes involved in memory self-monitoring. Although metamemory has been studied in cognitive psychology for several decades, there have been fewer studies investigating the neuropsychology of metamemory. In recent years, a growing number of studies of neurological patient groups have been conducted in order to investigate the neural correlates of metamemory. In this review, we examine the neuropsychological evidence that the frontal lobes are critically involved in monitoring and control processes, which are the central components of metamemory. The following conclusions are drawn from this literature: (1) There is a strong correlation between indices of frontal lobe function or structural integrity and metamemory accuracy (2) The combination of frontal lobe dysfunction and poor memory severely impairs metamemorial processes (3) Metamemory tasks vary in subject performance levels, and quite likely, in the underlying processes these different tasks measure, and (4) Metamemory, as measured by experimental tasks, may dissociate from basic memory retrieval processes and from global judgments of memory.

Impaired recruitment of the dorsolateral prefrontal cortex and hippocampus during encoding in bipolar disorder

BACKGROUND

The aim of the present study was to examine the functional neuroanatomy of episodic memory impairment in euthymic subjects with bipolar I disorder. There is evidence that individuals with bipolar disorder have cognitive impairments not only during mood episodes but also when they are euthymic. The most consistently reported cognitive difficulty in euthymic subjects with bipolar disorder is impairment in verbal episodic memory (i.e., the ability to learn new verbal information).

METHODS

The current study examined verbal learning in eight euthymic, remitted subjects with bipolar I disorder (BP-I; seven nonmedicated) and eight control subjects matched for age, gender, education, and intelligence. Subjects underwent (15)O-CO(2) positron emission tomography scanning while completing a verbal learning paradigm that consisted of encoding (learning) several lists of words.

RESULTS

The BP-I subjects had more difficulties learning the lists of words compared with the control subjects. Compared with control subjects, BP-I subjects exhibited blunted regional cerebral blood flow (rCBF) increases in the left dorsolateral prefrontal cortex (Brodmann's area 9/46) during encoding.

CONCLUSIONS

Consistent with previous studies, subjects with BP-I were impaired in learning new verbal information. This was associated with rCBF abnormalities in brain regions involved in learning and episodic memory.

Short-term verbal memory deficits in patients with obsessive-compulsive disorder

Recent neuropsychological studies have found deficits in the verbal memory of patients with obsessive-compulsive disorder. Difficulties in using organizational strategies were presumed to be the cause. Preceding studies did not look closely at their ability of feature detection of stimuli. Efficiency in feature detection is crucial to use the attributes or feature of stimuli as a clue in memory tasks. We examined verbal memory deficit and the ability of feature detection in Japanese patients with obsessive-compulsive disorder. We administered Iddon et al.'s verbal strategy task to 16 patients with obsessive-compulsive disorder and 16 healthy controls. The feature of Iddon et al.'s task was to include a phase that showed subjects the semantic structure of the task and timed each subject's analysis of the organization. Patients with obsessive-compulsive disorder were slower to classify stimuli words into semantic categories than were healthy controls. They recalled and recognized significantly fewer words than did healthy controls. In recall tasks, they used less organizational strategy than did healthy controls. Patients with obsessive-compulsive disorder were slower to analyze features of stimuli words than were healthy controls. This slowness possibly contributes to impaired memory performances that patients showed during the encoding process, since the efficient use of organizational strategies in limited time is difficult for them.

Recognition memory in Parkinson's disease with and without dementia: evidence inconsistent with the retrieval deficit hypothesis

Parkinson's disease (PD) has been associated with a pattern of performance on memory tests in which free recall is impaired but recognition and cued recall are intact, indicating problems with memory retrieval. Recent findings suggest that PD patients exhibit deficits in recognition as well as free recall, however. The current study set out to provide clear evidence that recognition and cued recall are not intact in PD. Ninety-nine idiopathic PD patients were administered the California Verbal Learning Test and their performance was compared to a well-matched normative sample. A profile analysis revealed that nondemented patients exhibited deficits on measures of cued recall and delayed recognition that were similar in magnitude to that of free recall. This was also the case for the cued recall deficits exhibited by demented patients; however, in this group recognition was worse than free recall. In both groups poor recognition appeared due to an elevated number of false positive errors. These results are inconsistent with the retrieval deficit hypothesis but support the notion that PD memory problems are secondary to prefrontal dysfunction.

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.

Spontaneous and directed application of verbal learning strategies in bipolar disorder and obsessive-compulsive disorder

OBJECTIVES

Individuals with bipolar disorder exhibit neuropsychological impairments when they are euthymic (neither depressed nor manic). One of the most consistently reported cognitive problems in euthymic individuals with bipolar disorder is impairment in verbal episodic memory. Recent findings suggest that episodic memory difficulties in these individuals are attributable to difficulties using organizational strategies during encoding. The purpose of the present study was (i) to investigate whether difficulties using organizational strategies in bipolar disorder are due to a failure in spontaneously initiating verbal organization strategies or are due to difficulties implementing such strategies, and (ii) to compare the characteristics of verbal organizational impairment in bipolar disorder with those observed in individuals with obsessive-compulsive disorder (OCD).

METHODS

Study participants were 20 individuals with bipolar I disorder (BP-I), 20 individuals with OCD, and 20 healthy control participants matched for age, gender, and education. Participants completed a verbal encoding paradigm that involved spontaneous and directed use of verbal organization strategies during encoding of word lists.

RESULTS

Compared with control subjects, both BP-I and OCD participants showed impaired verbal organization in the spontaneous encoding condition. In the directed encoding condition, OCD patients organized the word lists as well as control participants whereas BP-I participants exhibited lower verbal organization than both control and OCD participants. OCD and BP-I participants' free recall performance did not differ from that of control participants in the spontaneous encoding condition. In the directed encoding condition, BP-I participants recalled fewer words than OCD or control participants.

CONCLUSIONS

Episodic memory difficulties in OCD are associated with difficulties spontaneously initiating verbal organization strategies during encoding whereas the ability to implement verbal organization when instructed to do so is preserved. BP-I participants, on the other hand, exhibit difficulties in both spontaneously initiating verbal organization strategies and in the ability to implement such strategies when instructed to do so.

Memory perception and strategy use in Parkinson's disease

Although there is growing support for the existence of memory deficits within Parkinson's disease (PD), little has been done to evaluate the extent to which PD patients demonstrate differences in their use of metacognitive strategies. In the present study, 79 PD patients (46 men and 33 women) and 49 age-matched healthy participants (19 men and 30 women) were compared on a metamemory questionnaire. PD patients reported significantly less strategy-use than age-matched controls, particularly with regards to external memory strategies (such as making lists). This suggests that auxiliary treatments such as memory strategy training might be effective in this population.

Deficient Strategic Control of Verbal Encoding and Retrieval in Individuals With Methamphetamine Dependence

Methamphetamine (MA) dependence is associated with deficits in episodic verbal memory, but the cognitive mechanisms underlying such impairments are not known. The authors evaluated a component process model of episodic verbal memory in 87 persons with MA dependence (MA+) and 71 demographically similar non-MA-using controls (MA-). Compared with MA- controls, MA+ participants demonstrated deficient overall learning, free recall, and utilization of semantic clustering, as well as higher rates of repetitions and intrusions. No between-groups differences were evident on measures of serial clustering, retention, or recognition discrimination. Taken together, these findings indicate that MA dependence is associated with deficient strategic (i.e., executive) control of verbal encoding and retrieval, which is consistent with the sequelae of MA-related prefronto-striatal circuit neurotoxicity.

Impaired intentional content learning but spared incidental retention of contextual information in non-demented patients with Parkinson's disease

We investigated the incidental and intentional learning performance of 29 patients with idiopathic Parkinson's disease (PD) and 20 healthy volunteers. Measures of incidental and intentional memory were assessed with a spoken verbal recall task followed by a temporal word order task, a picture recall task followed by a spatial picture location task, and a written word recall task followed by a judgement of word frequency task. A multivariate analysis of variance and appropriate post hoc tests revealed significant differences for all intentional learning variables. In all cases, PD patients performed worse than normal controls. No group differences were found for the incidental retention of contextual information. The results indicate that PD patients have a selective problem of intentional learning, whereas incidental learning of contextual information remains intact. Elaborate processing, attentional and organizing strategies in the systematic encoding, and recollection of information have been attributed to dorsolateral prefrontal activation. Preferential dysfunction of dorsolateral prefrontal cortex-associated memory processes is consistent with the previously reported uneven patterns of dopamine loss in the striatum of patients with idiopathic PD showing most severe dopamine depletion in the portion of the caudate nucleus that is anatomically connected to the dorsolateral frontal cortex.

Bilateral nigral 6-hydroxydopamine lesions increase the amount of extracellular dopamine in the nucleus accumbens

The goal of the present study was to provide neurochemical evidence for a shift in the functional balance between the nigrostriatal and mesolimbic pathway in favour of the mesolimbic pathway by investigating the effects of a partial, nigral, bilateral 6-hydroxydopamine lesion on basal and novelty-induced extracellular dopamine release in the accumbens of Low responder rats to novelty (LR). Low responders were chosen because the above-mentioned shift was seen in LR rats, but not in rats that have a high response to novelty (HR). About 1 microg/microl of 6-hydroxydopamine was injected bilaterally into the substantia nigra pars compacta and a guide cannula was placed into the right accumbens. Changes in extracellular dopamine in response to novelty, a new cage, were measured using a microdialysis probe inserted into the accumbens. The lesion size was determined by quantification of tyrosine hydroxylase immunoreactivity of the substantia nigra and the ventral tegmental area. This revealed that the lesion partly destroyed the dopaminergic cells of the nigrostriatal pathway, thereby relatively sparing the dopaminergic cells of the mesolimbic pathway. The lesion significantly increased the amount of extracellular dopamine in the accumbens during both basal and novelty conditions. We suggest that the experimentally induced neuronal death in the substantia nigra pars compacta with subsequent removal of lateral inhibition of adjacent neurons underlies the observed changes in the amount of extracellular dopamine in the accumbens.

The contribution of the study of neurodegenerative disorders to the understanding of human memory

Memory impairment is one of the most common complaints affecting patients with neurodegenerative disorders, and its investigation has provided insights into the function and properties of human memory. The study of Alzheimer's disease has indicated the importance of mesial temporal structures and the hippocampus in episodic memory. In progressive supranuclear palsy, frontotemporal dementias, Parkinson's disease and Huntington's disease fronto-striatal networks are involved in working memory and higher level cognition. The study of semantic dementia, where there is lobar atrophy of the temporal lobe, has shown that the temporal neocortex has an important function in semantic memory. The investigation of human memory in neurodegenerative disorders suggests that the interaction of networks subserving episodic memory, semantic memory, and working memory contributes to higher level cognition and results in the fundamental homeostatic processes of recall and learning.

Interaction between the Human Hippocampus and the Caudate Nucleus during Route Recognition

Navigation through familiar environments can rely upon distinct neural representations that are related to different memory systems with either the hippocampus or the caudate nucleus at their core. However, it is a fundamental question whether and how these systems interact during route recognition. To address this issue, we combined a functional neuroimaging approach with a naturally occurring, well-controlled human model of caudate nucleus dysfunction (i.e., preclinical and early-stage Huntington's disease). Our results reveal a noncompetitive interaction so that the hippocampus compensates for gradual caudate nucleus dysfunction with a gradual activity increase, maintaining normal behavior. Furthermore, we revealed an interaction between medial temporal and caudate activity in healthy subjects, which was adaptively modified in Huntington patients to allow compensatory hippocampal processing. Thus, the two memory systems contribute in a noncompetitive, cooperative manner to route recognition, which enables the hippocampus to compensate seamlessly for the functional degradation of the caudate nucleus.

Striatal dopamine and learning strategy-an (123)I-FP-CIT SPECT study

Patients with Parkinson's disease (PD) have difficulty in processing learning tasks that lack external guidelines and, consequently, necessitate the subjects to generate their own problem-solving strategy. While the contribution of striatal dopaminergic deficiency to PD-specific motor symptoms is well established, its role in the PD-characteristic deviant learning style remains unclear. The aim of this study was to assess the relation between striatal dopamine activity as revealed by single photon emission computed tomography (SPECT) with (123)I-FP-CIT, a ligand for the dopamine transporter (DaT), and type of learning strategy, as identified by the California Verbal Learning Task (CVLT) in 19 patients with probable PD. The results showed a robust inverse correlation between striatal dopamine DaT binding and the externally guided, serial learning strategy: the lower the DaT in caudate nucleus as well as in putamen, the more the patient group appeared to rely on externally structured learning. Additionally, a significant positive correlation was found between caudatal DaT activity and the internally generated, semantic learning strategy. Unlike these strategic learning characteristics, IQ equivalent and recall total score appeared to vary independently from striatal DaT availability.

CONCLUSION

our findings provide direct evidence that striatal dopaminergic activity is specifically involved in the regulation of strategic learning processes.

Episodic memory impairment in bipolar disorder and obsessive-compulsive disorder: the role of memory strategies

BACKGROUND

There is evidence that individuals with bipolar disorder exhibit neuropsychological impairments not only during mood episodes but also when they are euthymic. One of the most consistently reported cognitive problems in euthymic individuals with bipolar disorder is an impairment in verbal episodic memory. Verbal learning and memory depend on individuals' ability to organize verbal information appropriately during learning. The purpose of the present study was (i) to determine whether episodic memory impairment in euthymic individuals with bipolar disorder is mediated by impairments in organization of verbal information during learning and (ii) to compare the characteristics of memory impairment in bipolar disorder with that previously found in obsessive-compulsive disorder (OCD).

METHODS

Study participants were 30 individuals with DSM-IV bipolar I disorder (BP-I), 30 individuals with DSM-IV OCD and 30 normal control participants matched for age, gender and education. Participants completed the California Verbal Learning Test (CVLT), a well-established measure of verbal learning and memory that enables assessment of verbal organization strategies during learning.

RESULTS

Compared with control subjects, both BP-I and OCD participants showed impaired performance in long-delayed free recall and verbal organization strategies during learning. BP-I participants showed greater long-delay free recall difficulties but not greater verbal organization difficulties during learning than OCD participants. For OCD participants, the long-delay recall impairment was mediated by difficulties using verbal organizational strategies during learning. In contrast, the group difference in long-delayed free recall between BP-I and control participants remained significant even when semantic clustering was introduced as a mediator. This indicated that BP-I participants' long-delayed free recall difficulties were mediated to a lesser extent by difficulties using verbal organizational strategies than for OCD participants.

CONCLUSIONS

Verbal episodic memory problems in individuals with bipolar I disorder and OCD are mediated to different degrees by difficulties using semantic clustering encoding strategies compared with control participants.

Semantic Organization and Verbal Memory Efficiency in Patients With Schizophrenia

The role of semantic organization in verbal memory efficiency in schizophrenia was investigated. Patients and healthy controls were administered a free-recall task involving 1 nonsemantically organizable list, 1 list organizable in semantic categories with typical instances, and 1 list organizable in semantic categories with atypical instances. Reduced semantic organization was observed in patients. Regression analyses showed that the semantic clustering score in the atypical organizable list made a significant contribution to recall performance in patients. When semantic clustering was controlled, the effect of diagnosis on free recall was significant. These results suggest that depth of semantic organization is a crucial factor of verbal memory performance in schizophrenia. However, semantic organizational deficit does not account for the whole recall impairment.

Verbal learning and memory in schizophrenic and Parkinson's disease patients

The purpose of this study was to investigate the neurofunctional substrate of verbal learning and memory impairments in schizophrenic patients. In this pilot study, our aim was to compare the memory disturbance of schizophrenic patients to the subcortico-frontal memory profile of Parkinson's disease (PD) patients. The California Verbal Learning Test, a verbal episodic memory test, was administered to 60 subjects, 20 patients with schizophrenia, 20 patients with PD and 20 healthy control subjects. All subjects were aged between 50 and 70 years and all patients were in a stable phase. Like the Parkinson patients, the schizophrenic patients showed a major deficit of retrieval characterized by deficit of recalls but contrarily to PD patients, schizophrenic patients' encoding scores were altered. These impairments in episodic memory could suggest a dysfunction of the subcortico-frontal circuits in schizophrenic patients. However, they demonstrated an additional encoding deficit associated with probable frontal in situ alteration.

Memory and executive function impairment predict dementia in Parkinson's disease

We analyzed the association of neuropsychological test impairment at baseline with the development of dementia in idiopathic Parkinson's disease (PD) patients. A cohort of nondemented PD patients from northern Manhattan, NY was followed annually with neurological and neuropsychological evaluations. The neuropsychological battery included tests of verbal and nonverbal memory, orientation, visuospatial ability, language, and abstract reasoning. The association of baseline neuropsychological tests scores with incident dementia was analyzed using Cox proportional hazards models. The analysis controlled for age, gender, education, duration of PD, and the total Unified Parkinson's Disease Rating Scale motor score at baseline. Forty-five out of 164 patients (27%) became demented during a mean follow-up of 3.7 +/- 2.3 years. Four neuropsychological test scores were significantly associated with incident dementia in the Cox model: total immediate recall (RR: 0.92, 95% CI: 0.87-0.97, P = 0.001) and delayed recall (RR: 0.73, 95% CI: 0.59-0.91, P = 0.005) of the Selective Reminding Test (SRT), letter fluency (RR: 0.87, 95% CI: 0.77-0.99, P = 0.03), and Identities and Oddities of the Mattis Dementia Rating Scale (RR: 0.85, 95% CI: 0.73-0.98, P = 0.03). When the analysis was performed excluding patients with a clinical dementia rating of 0.5 (questionable dementia) at baseline evaluation, total immediate recall and delayed recall were still predictive of dementia in PD. Our results indicate that impairment in verbal memory and executive function are associated with the development of dementia in patients with PD.

Perseveration in schizophrenia: failure to generate a plan and relationship with the psychomotor poverty subsyndrome

Although perseveration in the Wisconsin Card Sorting Test (WCST) has been studied extensively in schizophrenia, the underlying cognitive dysfunctions are not yet clear. In schizophrenia, perseveration has been found to relate to frontal and striatal abnormalities. Therefore, both a failure to generate a plan as seen in patients with frontal abnormalities, or a failure to execute a plan as observed in Parkinson patients, who suffer primarily from striatal abnormalities, could explain perseveration in schizophrenia. The aim of the present study was to distinguish between these two cognitive dysfunctions, which are described by Frith in his routes-to-action model. The main difference between these dysfunctions is the ability to use external guidance. In the present study, 39 schizophrenic patients and 36 healthy controls were assessed with the California Verbal Learning Test (CVLT) and the WCST, in which use of external guidance can be measured, and with the Positive and Negative Syndrome Scale (PANSS) to determine the relationship with symptomatology. The results showed that half of the schizophrenic patients showed perseveration, which could be explained by a failure to generate a plan and was related to the psychomotor poverty subsyndrome. No evidence was found for a failure to execute a plan. Type of antipsychotic medication used (atypical vs. typical) proved not relevant. The results are discussed in the light of evidence for involvement of the dorsolateral prefrontal cortex in perseveration in schizophrenia.

Spatial behaviour is driven by proximal cues even in mildly impaired Parkinson's disease

This investigation addresses the question whether patients with mild to moderate Parkinson's disease (PD) show spatial deficits in real-life settings. Therefore, a "search through"-locomotor task incorporating basic features of both the radial arm maze and the Morris water maze paradigms was used. The participants had to find and remember five out of twenty hidden locations within a completely controlled environment. Different spatial memory errors and inter-response intervals were recorded automatically. Fourteen patients with idiopathic PD and fourteen healthy controls matched for age, sex, handedness, and education were investigated. Patients and controls were widely comparable with respect to intelligence, verbal memory, and executive functions. Results show that performance deteriorated in about half of the patients if the starting position was moved by 90 degrees and the proximal cues were deleted simultaneously. This deficit was systematically related to specific measures of attention. Moreover, patients were less able to update their locomotor strategies towards a more effective strategy. Results are discussed with respect to the patient's inability to generate rules which can be flexibly used in changing environments, especially if proximal cues are removed. It is concluded that deficits in spatial behaviour can be elicited even in near-to-real-life situations if appropriate testing procedures are used.

Neuropsychological deficits in essential tremor: an expression of cerebello-thalamo-cortical pathophysiology?

Few studies have been published regarding the neuropsychological characteristics of patients with essential tremor (ET), but preliminary findings suggest that mild attentional and executive dysfunction accompany the disorder. A consecutive series of 101 patients with ET referred for thalamotomy and/or thalamic deep brain stimulation candidacy work-up also underwent neuropsychological evaluation. Average neuropsychological test scores were calculated, along with the proportions of subjects whose scores fell within or more than one SD above or below the mean (using demographically corrected normative data). Significantly lower than average (T-score of 50) scores were evident on measures of complex auditory attention, visual attention and response inhibition, recall of a word list, verbal fluency, and visual confrontation naming. A significantly greater proportion of patients (ranging from about 34 to 60%) than might be expected on the basis of a normal distribution obtained scores more than one SD below the normative mean on select measures of attention, verbal fluency, immediate word list recall, semantic encoding, and facial matching. Consistent with prior research, notable, albeit clinically subtle, deficits in attention and select executive functions are evident in patients with ET. Although not specific to ET or cerebellar dysfunction, the observed pattern of cognitive deficits is consistent with cerebello-thalamo-cortical circuit dysfunction.

Differential effects of a small, unilateral, 6-hydroxydopamine-induced nigral lesion on behavior in high and low responders to novelty

The goal of this study was to develop an animal model that evaluates striatal-specific behavior after partial, unilateral destruction of nigrostriatal neurons. 6-OHDA (1 microg) was injected intranigrally (day 0) to reduce dopaminergic innervation of the dorsal striatum (DS); 6-OHDA (5 microg) was injected to reduce innervation of DS and nucleus accumbens (ACC). We analyzed changes in (a) behavior regulated by dopamine (DA) release in the DS (hindpaw preference from day 5 to day 19, every other day) and the ACC (novelty-induced locomotion on day 16) and (b) apomorphine-induced rotation (on day 21). We used two types of rat that show differences in structure and function of the dopaminergic neurons, namely high (HR) and low (LR) responders to novelty. 6-OHDA (1 microg) significantly decreased TH immunoreactivity (TH-ir) in the DS and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. Only in LRs was the significant increase of novelty-induced locomotion accompanied by a significant increase in TH-ir density in the ACC: this suggests a lesion-induced shift in nigrostriatal/mesolimbic balance toward a dominance of the mesolimbic system. The higher 6-OHDA dose significantly decreased TH-ir in the DS and the ACC and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. However, this increase occurred significantly earlier in LRs than in HRs. Apomorphine elicited contralateral rotations solely in LRs, and not in HRs, indicating development of supersensitive dopamine receptors in the DS of LRs, but not HRs. The data show that LRs are more susceptible to 6-OHDA than HRs. The relevance of the present data for Parkinson's disease is discussed.

Is the HM story only a "remote memory"? Some facts about hippocampus and memory in humans

In this review, we argue that a number of current data support the notion that the hippocampal formations play an important role in episodic memory in humans. We will focus on data gathered from three topics within this field: (1) the neuropsychological study of memory in degenerative diseases, which provides striking dissociations of processes, as a function of the location of cerebral lesions and of their functional consequences; (2) the description of patients' memory difficulties after unilateral medial temporal lobectomy. Given the visuo-verbal dissociation, we may anticipate that the study of the effects of such lesions may help in the understanding of the role of the hippocampus in memory, in terms of: (i) the stage of memory processing where the hippocampus is really involved (encoding, consolidation and/or retrieval); (ii) the specificity of the impairments as a function of the nature (verbal vs. visuo-spatial) of the to-be-remembered material; (3) recent evidence from imaging studies: (i) the morphological approach, which provides interesting information with the study of correlations between the volumes of diverse cerebral regions-particularly the volume of the hippocampus-and episodic memory performance and other cognitive measures; (ii) metabolic studies, using PET scan, which were first designed for correlational analyses between performance in episodic memory tasks and glucose utilization at rest in diverse regions of interest, such as the hippocampal formations; (iii) activation studies with PET and functional MRI, which are actually more straightforward, since they allow correlations between the metabolism in regions of interest and performance on line (e.g. during encoding or retrieval of information). In our view, inasmuch as such different approaches-degenerative diseases, lesions or imagery-provide convergent information, they give renewed weight to the notion according to which the hippocampal formations are critically concerned in episodic memory processes.

Basal ganglia dysfunction, working memory, and sentence comprehension in patients with Parkinson's disease

To investigate the role of the basal ganglia in working memory and sentence comprehension, 14 patients with Parkinson's disease (PD) were administered experimental measures of semantic and phonological working memory, and a measure of sentence comprehension, while receiving dopaminergic medications and after a period of withdrawal from these medications. An age- and education- matched control group (N=14) received the same measures. Comparison with control subjects revealed deficits in patients with PD in sentence processing regardless of medication status, but no deficits in working memory. In contrast to previous studies, withdrawal of dopaminergic medications had no significant impact on task- related working memory functions or on sentence comprehension. Results suggest that basal ganglia dysfunction does not solely account for sentence comprehension deficits seen in PD.

Cognitive styles in high-functioning adolescents with autistic disorder

This study addressed the operationalization, the identification, and the prevalence of weak central coherence and poor cognitive shifting in 35 high-functioning adolescents with autism. Central coherence and cognitive shifting were represented by two factors in a factor analysis, each reflecting a constituent aspect of the domain in question. With regard to central coherence, these aspects were the ability of piecemeal processing and the ability to process meaning. The aspects related to cognitive shifting concerned internally and externally controlled shifting. Weak central coherence and poor cognitive shifting did not appear to be related to measures of symptom severity, social understanding, and social competence. Both these cognitive styles did not appear to be universal to autism. In our sample, weak central coherence and poor cognitive shifting were found to be significantly more common than in normative control subjects.

Strategic processing and episodic memory impairment in obsessive compulsive disorder

There is evidence that nonverbal memory problems in obsessive compulsive disorder (OCD) are mediated by impaired strategic processing. Although many studies have found verbal memory to be normal in OCD, these studies did not use tests designed to stress organizational strategies. This study examined verbal and nonverbal memory performance in 33 OCD patients and 30 normal control participants with the Rey-Osterrieth Complex Figure Test and the California Verbal Learning Test. OCD patients were impaired on verbal and nonverbal measures of organizational strategy and free recall. Multiple regression modeling indicated that free recall problems in OCD were mediated by impaired organizational strategies used during learning trials. Therefore, verbal and nonverbal episodic memory deficits in OCD are affected by impaired strategic processing. Results are consistent with neurobiological models proposing frontal-striatal system dysfunction in OCD.

Organizational strategies mediate nonverbal memory impairment in obsessive-compulsive disorder

BACKGROUND

Previous neuropsychological studies of obsessive-compulsive disorder (OCD) have indicated impaired executive functioning and nonverbal memory. The extent to which impaired executive functioning impacts nonverbal memory has not been established. The current study investigated the mediating effects of organizational strategies used when copying a figure on subsequent nonverbal memory for that figure.

METHODS

We examined neuropsychological performance in 20 unmedicated subjects with OCD and 20 matched normal control subjects. Subjects were administered the Rey-Osterrieth Complex Figure Test (RCFT) and neuropsychological tests assessing various aspects of executive function.

RESULTS

OCD subjects differed significantly from healthy control subjects in the organizational strategies used to copy the RCFT figure, and they recalled significantly less information on both immediate and delayed testing. Multiple regression analyses indicated that group differences in immediate percent recall were significantly mediated by copy organizational strategies. Further exploratory analyses indicated that organizational problems in OCD may be related to difficulties shifting mental and/or spatial set.

CONCLUSIONS

Immediate nonverbal memory problems in OCD subjects were mediated by impaired organizational strategies used during the initial copy of the RCFT figure. Thus, the primary deficit was one affecting executive function, which then had a secondary effect on immediate memory. These findings are consistent with current theories proposing frontal-striatal system dysfunction in OCD.