Parkinson Disease: Maddox WT

Price A, Filoteo JV, Maddox WT. · Department of Psychology, Elizabethtown College, Elizabethtown, PA 17022, United States. · Neuropsychologia. · Pubmed #19428385 links to  free full text

Abstract: Measures of explicit rule-based category learning are commonly used in neuropsychological evaluation of individuals with Parkinson's disease (PD) and the pattern of PD performance on these measures tends to be highly varied. We review the neuropsychological literature to clarify the manner in which PD affects the component processes of rule-based category learning and work to identify and resolve discrepancies within this literature. In particular, we address the manner in which PD and its common treatments affect the processes of rule generation, maintenance, shifting and selection. We then integrate the neuropsychological research with relevant neuroimaging and computational modeling evidence to clarify the neurobiological impact of PD on each process. Current evidence indicates that neurochemical changes associated with PD primarily disrupt rule shifting, and may disturb feedback-mediated learning processes that guide rule selection. Although surgical and pharmacological therapies remediate this deficit, it appears that the same treatments may contribute to impaired rule generation, maintenance and selection processes. These data emphasize the importance of distinguishing between the impact of PD and its common treatments when considering the neuropsychological profile of the disease.

Maddox WT, Aparicio P, Marchant NL, Ivry RB. · Department of Psychology, University of Texas, Austin 78712, USA. · J Cogn Neurosci. · Pubmed #15904539 No free full text.

Abstract: The basal ganglia and cerebellum have both been implicated in motor skill acquisition. Recent hypotheses concerning cognitive functions of the basal ganglia and cerebellum have emphasized that these subcortical structures may also contribute to nonmotor learning. To explore this issue, patients with Parkinson's disease (PD) and patients with cerebellar lesions (CB) were tested on two category-learning tasks. Identical stimulus displays were used for the two tasks, consisting of a reference line and target line. In the length task, the two categories were defined based on the length of the target line. In the distance task, the two categories were defined by the distance between the target and reference lines. Thus, both categories could be defined by a simple rule in which attention must be restricted to a single relevant dimension. Consistent with previous results, the patients with PD were impaired on both tasks compared with neurologically healthy controls. In contrast, the CB patients performed similar to the control participants. Model-based analyses indicate that the patients with PD were able to select the appropriate categorization rule, but that they adopted suboptimal category boundaries in both conditions and were more variable in the application of the selected rule. These results provide an important neuropsychological dissociation on a non-motor-learning task between the effects of basal ganglia and cerebellar lesions. Moreover, the modeling work suggests that at least part of the Parkinson patients' impairment on these tasks reflect a tendency to exhibit strong response biases.

Filoteo JV, Maddox WT. · Department of Psychology, University of Utah, Salt Lake City 84112, USA. · Neuropsychology. · Pubmed #10353372 No free full text.

Abstract: Parkinson's disease (PD) patients and normal controls (NCs) were administered a series of visual attention tasks. The dimensional integration task required integration of information from 2 stimulus dimensions. The selective attention task required selective attention to 1 stimulus dimension while ignoring the other stimulus dimension. Both integral- and separable-dimension stimuli were examined. A series of quantitative models of attentional processing was applied to each participant's data. The results suggest that (a) PD patients were not impaired in integrating information from 2 stimulus dimensions, (b) PD patients were impaired in selective attention, (c) selective attention deficits in PD patients were not due to perceptual interference, and (d) PD patients were affected by manipulations of stimulus integrality and separability in much the same way as were NCs.

Filoteo JV, Maddox WT, Salmon DP, Song DD. · Department of Psychiatry, University of California, San Diego, CA 92161, USA. · Neuropsychology. · Pubmed #17402818 No free full text.

Abstract: Nondemented patients with Parkinson's disease (PD) are impaired in learning to categorize simple perceptual stimuli when category membership is defined by a nonlinear relationship between stimulus dimensions but not when the relationship is linear (J. V. Filoteo, W. T. Maddox, D. P. Salmon, & D. D. Song, 2005). In the present study, the authors examined whether performance in either of these 2 category learning conditions was predictive of global cognitive decline following a mean of 1.6 years since the time patients were 1st seen. Results indicated that final block accuracy in the nonlinear condition, but not the linear condition, predicted global cognitive decline. Performance on the Wisconsin Card Sorting Test (WCST) did not significantly predict global cognitive decline, although there was a trend for this to be the case. In addition, the association between nonlinear category learning and global cognitive decline was not impacted by patients' performance on the WCST. Results suggest that nonlinear category learning predicts cognitive decline in nondemented patients with PD and that nonlinear category learning and WCST performances may provide independent measures of integrity of the posterior and anterior caudate, respectively.

Filoteo JV, Maddox WT, Ing AD, Song DD. · University of California, San Diego, CA, USA. · Neuropsychologia. · Pubmed #16978666 No free full text.

Abstract: Parkinson's disease (PD) patients and normal controls were tested in three category learning experiments to determine if previously observed rule-based category learning impairments in PD patients were due to deficits in selective attention or working memory. In Experiment 1, optimal categorization required participants to base their decision on a single stimulus dimension and ignore irrelevant variation on another dimension, thus emphasizing selective attention processes. In Experiment 2, optimal categorization required participants to base their decision on both stimulus dimensions using a conjunction of unidimensional decisions. Thus, this task placed less emphasis on selective attention and more on working memory. In Experiment 3, optimal categorization again required participants to base their decision on both stimulus dimensions using a disjunction of two unidimensional decisions in which an additional verbal operation was needed, thereby placing even greater emphasis on working memory. Results indicated that PD patients were impaired in the unidimensional rule-based condition, but not the other two rule-based conditions. These results are consistent with previous studies that demonstrate that PD patients are impaired in learning rule-based categories when selective attention demands are greatest, whereas these patients are normal in learning rule-based tasks when working memory demands are emphasized. Overall, these findings help to delineate the conditions under which PD patients display rule-based category learning deficits.

Filoteo JV, Maddox WT, Ing AD, Zizak V, Song DD. · Department of Psychology, University of California, San Diego, California, USA. · J Int Neuropsychol Soc. · Pubmed #16212677 No free full text.

Abstract: This study examined the impact of irrelevant dimensional variation on rule-based category learning in patients with Parkinson's disease (PD), older controls (OC), and younger controls (YC). Participants were presented with 4-dimensional, binary-valued stimuli and were asked to categorize each into 1 of 2 categories. Category membership was based on the value of a single dimension. Four experimental conditions were administered in which there were zero, 1, 2, or 3 randomly varying irrelevant dimensions. Results indicated that patients with PD were impacted to a greater extent than both the OC and YC participants when the number of randomly varying irrelevant dimensions increased. These results suggest that the degree of working memory and selective attention requirements of a categorization task will impact whether PD patients are impaired in rule-based category learning, and help to clarify recent discrepancies in the literature.

Filoteo JV, Maddox WT, Salmon DP, Song DD. · Department of Psychiatry, University of California, San Diego, CA, USA. · Neuropsychology. · Pubmed #15769205 No free full text.

Abstract: Information-integration category learning was examined in patients with Parkinson's disease (PD) and in healthy control participants in 2 different conditions. In the linear condition, optimal categorization required a nonverbalizable linear integration of information from the 2 stimulus dimensions, whereas in the nonlinear condition, a nonlinear integration of information was required. Each participant completed 600 trials in each condition and was given corrective feedback following each trial. Results indicated that PD patients were not impaired in the linear condition across all trials, whereas the same patients were impaired in the nonlinear condition, but only later in training. The authors conducted model-based analyses to identify participants who used an information-integration approach, and a comparison of the accuracy rates of those individuals further revealed a specific deficit in information-integration category learning in patients with PD. These findings suggest that the striatum may be particularly involved in information-integration category learning when the rule is highly complex.

Maddox WT, Filoteo JV. · Department of Psychology, University of Texas, Austin 78712, USA. · J Int Neuropsychol Soc. · Pubmed #11575593 No free full text.

Abstract: The contribution of the striatum to category learning was examined by having patients with Parkinson's disease (PD) and matched controls solve categorization problems in which the optimal rule was linear or nonlinear using the perceptual categorization task. Traditional accuracy-based analyses, as well as quantitative model-based analyses were performed. Unlike accuracy-based analyses, the model-based analyses allow one to quantify and separate the effects of categorization rule learning from variability in the trial-by-trial application of the participant's rule. When the categorization rule was linear, PD patients showed no accuracy, categorization rule learning, or rule application variability deficits. Categorization accuracy for the PD patients was associated with their performance on a test believed to be sensitive to frontal lobe functioning. In contrast, when the categorization rule was nonlinear, the PD patients showed accuracy, categorization rule learning, and rule application variability deficits. Furthermore, categorization accuracy was not associated with performance on the test of frontal lobe functioning. Implications for neuropsychological theories of categorization learning are discussed.