H.J.C. Berger

Memory and learning strategies in patients with Parkinson's disease

Parkinsons disease patients (PD) do not differ from control subjects (CS) when they have to execute a problem solving task in which external cues for solving the problem are given. However, when PD have to solve a problem by means of an internally generated strategy, they show a serious decrease in performance. We hypothesised that this distinction may also apply to the way PD and CS organize recall. In order to test our hypothesis the California Verbal Learning Test (CVLT) was administered to 59 PD and 30 CS. The test consists of five learning trials using a 16-word target list, composed of four items from each of four semantic categories. The fact that the word list was built on this implicit organization was not divulged in advance. The sequence in which the words were read is fixed; each subsequent word belongs to a category being different from the category to which the preceding word belongs. The organization in recall according to the semantic categories is considered to be the result of an unprompted, internally generated strategy. Recall according to the sequence in which the words are read by the experimenter, is viewed as an externally offered strategy. The results prove to be in line with our hypothesis: unlike CS who appeared to rely mainly and increasingly on an internally generated semantic organization, PD showed evidence of gradually adhering more to the externally imposed serial sequence.

Severity of Parkinson's disease is a risk factor for peak-dose dyskinesia.

Fifty four patients with idiopathic Parkinsons disease receiving levodopa therapy were studied. Thirty three of these patients displayed peak-dose dyskinesia. Neither the duration of Parkinsons disease nor the duration of levodopa therapy discriminated between patients with and patients without peak-dose dyskinesia. Consequently, these criteria could not determine whether the first appearance of peak-dose dyskinesia depends on the duration of Parkinsons disease--a factor that is related to the severity of the disease--or on the duration of levodopa therapy. A subgroup of nineteen patients with unilateral or unequivocally asymmetrical peak-dose dyskinesia was examined 12 hours after withdrawal of levodopa. A levodopa testdose provoked unilateral or unilateral preponderant peak-dose dyskinesia which always involved the most severely affected side and which also happened to be the side of onset of the disease. This demonstrates that the severity of Parkinsons disease is the main risk factor for peak-dose dyskinesia.

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.

Bimanual simultaneous motor performance and impaired ability to shift attention in Parkinson's disease.

The ability to share time and to shift attention between bimanual simultaneous motor tasks were studied in 18 patients with Parkinsons disease (PD) and 19 age- and intelligence-matched controls. The task consisted of drawing triangles with the dominant hand and squeezing a rubber bulb with the nondominant hand. Motor performance was measured using the variables: amplitude of squeezing, frequency of squeezing and velocity of drawing triangles. After eliminating variance due to baseline differences in single-handed performance, the bimanual simultaneous performance of PD and controls turned out to be similar to the frequency of squeezing and the velocity of drawing triangles. The amplitude of squeezing, however, differed between the two groups: it was significantly reduced in PD. Arguably the disturbance in the bimanual performance of PD patients was not due to a disorder of time sharing, but to a decreased ability to shift attention from the visually cued task to the non visually cued task. The results agree with current evidence that PD patients are more impaired when they have to rely upon internal control for the regulation of shifting attention than when external cues are available.

Central Coherence and Cognitive Shifting in Relation to Social Improvement in High-Functioning Young Adults with Autism

The objective of this prospective study was to evaluate the possible role of two cognitive styles – weak central coherence and poor cognitive shifting – in predicting social improvement in patients with autistic disorder. Thirty patients, largely similar in age (young adults), intelligence (high-functioning) and living conditions (residential treatment in the same unit) were assessed at two separate time points with a 3-year interval between pretest and posttest. At pretest central coherence, cognitive shifting and several aspects of social functioning – symptom severity, social intelligence and social competence – were measured. At posttest social functioning was reassessed. Unlike central coherence, cognitive shifting was identified as a significant prognostic marker. This differential outcome might be an indication that patients with poor cognitive shifting and patients with weak central coherence have different prognoses with the current, highly structured treatment milieu; it is unknown whether patients with poor cognitive flexibility might benefit more from treatments specifically designed to address this problem.

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 Parkinsons 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 Parkinsons 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.

Haloperidol and cognitive shifting

In this study haloperidol appeared to affect the performance on a selected category of cognitive tasks considered to represent shifting aptitude. A pretest--post-test design was used with two groups of subjects: 17 patients suffering from idiopathic spasmodic torticollis, and 17 controls who were matched for age and intelligence. The results are discussed in relation to previous findings on haloperidol and cognition, shifting disorder in Parkinsons disease and changes in behavioural organization found in animals with an experimentally induced dopaminergic hypoactivity.

MEMORY PERFORMANCE UNDER VARYING CUEING CONDITIONS IN PATIENTS WITH PARKINSON'S DISEASE

The present study is a continuation of a previous study in memory performance which showed that Parkinsons disease (PD) patients increasingly relied on explicit cues which prompt the external strategy of serial clustering, in comparison to control subjects (CS), who profited increasingly from implicit cues which prompt the internal and more effective strategy of semantic clustering. In this study, we investigated whether the recall of PD patients can be affected by adding or removing explicit cues. We manipulated the California Verbal Learning Test in two ways. First, we told the subjects under study in advance from which categories the items to be recalled were derived, thus making the implicit cue to cluster semantically explicit (explicit condition). Next, we permuted the sequence of the items in each trial, thus preventing the subjects from adhering to the serial order, i.e. to explicit cues (permuted condition). We included the data of our previous study (mixed condition) in the analysis of memory and learning performance in the three conditions. Learning of PD patients, as reflected in the semantic ratio, proved to be more affected by the cueing conditions than that of CS. Total performance and the serial ratios did not show a significant interaction between group and cueing condition. The results are discussed in terms of external and internal generation of problem-solving strategies.

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 Parkinsons 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.

Impaired cognitive shifting in parkinsonian patients on anticholinergic therapy

In this study we established that cognitive shifting, an ability that is known to be affected in PD, is more impaired in PD patients, treated with anticholinergics, than in de novo patients. Eleven PD patients on anticholinergic monotherapy were compared with 30 de novo patients. The groups did not differ with respect to age, duration and severity of PD, and depression, nor with respect to general intelligence or attention. We assessed cognitive shifting with three different card-sorting tests. The patients on anticholinergics showed a poorer performance on all card-sorting tests than the de novo patients did. The patients on anticholinergics needed significantly more trials in two card-sorting tests and discovered significantly less categories in total. There was also a significant difference in memory performance, but memory performance did not correlate with any score on the card-sorting tests. This indicates that the performance on card-sorting tests and the memory performance were independent.