Dissociation of Habit-Learning in Parkinson's and Cerebellar Disease

Abstract

Damage to the medial-temporal region is known to result in declarative (explicit) memory deficits but nondeclarative (implicit) memory is largely unaffected by such lesions. Earlier studies have shown that some forms of implicit learning depend on cerebellar circuits but remain preserved following affections of the basal ganglia circuits. It is unknown which forms of implicit learning persist in patients with cerebellar pathology but are affected after basal ganglia lesions. Therefore, we determined if a test sensitive for habit-learning (probabilistic classification task) resulted in normal values for patients with cerebellar disease but resulted in affected results in patients with Parkinson's disease (PD). To this end, 23 patients with PD, 16 patients with familial or idiopathic cerebellar degeneration (CD), and 20 controls were tested for habit-learning. There was no impairment of patients with CD for the early learning period but there was abnormal learning in the PD group. For a later learning period, the patients with the PD showed improved performance. We conclude that the probabilistic learning task is an implicit, nonmotor learning task which is sensitive for basal ganglia pathology but remains unaffected in the case of cerebellar pathology. Such a test may be of special interest for the detection and possible neurobehavioral treatment of cognitive and motor deficits.

The effects of category overlap on information-integration and rule-based category learning

“…Even so, participants can achieve almost optimal accuracy with an explicit strategy in which they simply respond on the basis of the presence or absence of the most informative card (i.e., approximately 73% correct). Because the weatherprediction task is probabilistic, and optimal accuracy requires information integration, it has often been assumed that learning in the task is mediated by a single system that recruits some implicit, incremental process (Knowlton et al, 1996;Weickert et al, 2002;Witt, Nuhsman, & Deuschl, 2002). However, our results suggest that explicit strategies should be common in the weather-prediction task, because a simple explicit strategy is nearly optimal.…”

Models of probabilistic category learning in Parkinson’s disease: Strategy use and the effects of L-dopa

“…Research with the WPT has provided mixed results. Some studies showed that, compared to healthy controls, PD patients were impaired at early learning (Knowlton et al, 1996;Witt et al, 2002), but to a lesser extent (Knowlton et al, 1996) or not (Witt et al, 2002) in later learning. Other studies found impaired performance throughout the task (Shohamy et al, 2004b,a;Wilkinson et al, 2008).…”

“…One impetus for the claim of such dissociable learning systems was the finding that amnesic patients showed no (early) impairment in the WPT, whilst unable to recall recall certain aspects of the testing episode (Eldridge et al, 2002;Knowlton et al, 1994Knowlton et al, , 1996. Impaired WPT performance was not accompanied by this lack of declarative memory in PD patients (Knowlton et al, 1996;Sage et al, 2003;Witt et al, 2002). The double dissociation between learning performance and explicit recall has been taken as evidence for the existence of multiple memory systems (Ashby et al, 1998;Ashby and Maddox, 2005;Gabrieli, 1998;Knowlton et al, 1994Knowlton et al, , 1996Poldrack and Rodriguez, 2004;Shohamy et al, 2008).…”

“…This suggests that PD patients have particular problems in learning from feedback to their responses, which can be related to disrupted reward prediction errors. Neuroimaging studies with healthy individuals have shown increased activity in the striatum and decreased activity in the medial temporal lobes during the normal (feedback based) WPT (Poldrack et al, 2001;Witt et al, 2002). PD patients on the other hand show increased activation in the medial temporal lobes throughout the task, as well as lower activity in the dorsal striatum than controls (Witt et al, 2002).…”

“…Neuroimaging studies with healthy individuals have shown increased activity in the striatum and decreased activity in the medial temporal lobes during the normal (feedback based) WPT (Poldrack et al, 2001;Witt et al, 2002). PD patients on the other hand show increased activation in the medial temporal lobes throughout the task, as well as lower activity in the dorsal striatum than controls (Witt et al, 2002). The emerging picture is thus that, due to a disrupted striatal habit learning system, PD patients rely on a qualitatively different learning process, one that is explicit (declarative) rather than implicit (procedural).…”