Impaired sequential and partially compensated probabilistic skill learning in Parkinson's disease

What neurological diseases tell us about procedural perceptual-motor learning? A systematic review of the literature

INTRODUCTION

Procedural perceptual-motor learning of sequences (PPMLS) provides perceptual-motor skills in many activities of daily living. Based on behavioral and neuroimaging results, theoretical models of PPMLS postulate that the cortico-striatal loop, the cortico-cerebellar loop and the hippocampus are specifically involved in the early stage of PPMLS while the cortico-striatal loop would be specifically involved in the late stage of PPMLS. Hence, current models predict that the early stage of PPMLS should be impaired in Parkinson's disease (PD: lesion of the cortico-striatal loop), in cerebellar disease (CD: lesion of the cortico-cerebellar loop) and in Alzheimer's disease (AD: lesion of the hippocampus), whereas the late stage of PPMLS should be specifically impaired in PD.

OBJECTIVE

The aim of the study is (1) to draw a complete picture of experimental results on PPMLS in PD, CD and AD (2) to understand heterogeneity of results as regard to participant and task characteristics.

METHOD

This review is based on the guideline proposed by the PRISMA statement.

RESULTS

Our review reveals (1) that the experimental results clarify the theoretical models and (2) that the impairment of PPMLS depends on both the personal characteristics of the participants and the characteristics of the task to-be-learnt rather than on the disease itself.

CONCLUSION

Our results highlight that these characteristics should be more carefully considered to understand the heterogeneity of results across studies on PPMLS and the effects of rehabilitation programs.

Phasic Dopamine Changes and Hebbian Mechanisms during Probabilistic Reversal Learning in Striatal Circuits: A Computational Study

Cognitive flexibility is essential to modify our behavior in a non-stationary environment and is often explored by reversal learning tasks. The basal ganglia (BG) dopaminergic system, under a top-down control of the pre-frontal cortex, is known to be involved in flexible action selection through reinforcement learning. However, how adaptive dopamine changes regulate this process and learning mechanisms for training the striatal synapses remain open questions. The current study uses a neurocomputational model of the BG, based on dopamine-dependent direct (Go) and indirect (NoGo) pathways, to investigate reinforcement learning in a probabilistic environment through a task that associates different stimuli to different actions. Here, we investigated: the efficacy of several versions of the Hebb rule, based on covariance between pre- and post-synaptic neurons, as well as the required control in phasic dopamine changes crucial to achieving a proper reversal learning. Furthermore, an original mechanism for modulating the phasic dopamine changes is proposed, assuming that the expected reward probability is coded by the activity of the winner Go neuron before a reward/punishment takes place. Simulations show that this original formulation for an automatic phasic dopamine control allows the achievement of a good flexible reversal even in difficult conditions. The current outcomes may contribute to understanding the mechanisms for active control of dopamine changes during flexible behavior. In perspective, it may be applied in neuropsychiatric or neurological disorders, such as Parkinson’s or schizophrenia, in which reinforcement learning is impaired.

Cognition and motor learning in a Parkinson's disease cohort: importance of recall in episodic memory

Impaired motor learning in individuals with Parkinson's disease is often attributed to deficits in executive function, which serves as an important cognitive process supporting motor learning. However, less is known about the role of other cognitive domains and its association with motor learning in Parkinson's disease. The objective of this study was to investigate the associations between motor learning and multiple domains of cognitive performance in individuals with Parkinson's disease. Twenty-nine participants with Parkinson's disease received comprehensive neuropsychological testing, followed by practice of a bimanual finger sequence task. A retention test of the finger sequence task was completed 24 h later. Hierarchical linear regressions were used to examine the associations between motor learning (acquisition rate and retention) and cognitive performance in five specific cognitive domains, while controlling for age, sex, and years of Parkinson's disease diagnosis. We found that a higher acquisition rate was associated with better episodic memory, specifically better recall in visual episodic memory, in individuals with Parkinson's disease. No significant associations were observed between retention and cognitive performance in any domains. The association between motor acquisition and episodic memory indicates an increased dependency on episodic memory as a potential compensatory cognitive strategy used by individuals with Parkinson's disease during motor learning.