Implicit sequence learning in people with Parkinson’s disease

Abstract

Implicit sequence learning involves learning about dependencies in sequences of events without intent to learn or awareness of what has been learned. Sequence learning is related to striatal dopamine levels, striatal activation, and integrity of white matter connections. People with Parkinson’s disease (PD) have degeneration of dopamine-producing neurons, leading to dopamine deficiency and therefore striatal deficits, and they have difficulties with sequencing, including complex language comprehension and postural stability. Most research on implicit sequence learning in PD has used motor-based tasks. However, because PD presents with motor deficits, it is difficult to assess whether learning itself is impaired in these tasks. The present study used an implicit sequence learning task with a reduced motor component, the Triplets Learning Task (TLT). People with PD and age- and education-matched healthy older adults completed three sessions (each consisting of 10 blocks of 50 trials) of the TLT. Results revealed that the PD group was able to learn the sequence, however, when learning was examined using a Half Blocks analysis (Nemeth et al., 2013), which compared learning in the 1st 25/50 trials of all blocks to that in the 2nd 25/50 trials, the PD group showed significantly less learning than Controls in the 2nd Half Blocks, but not in the 1st. Nemeth et al. (2013) hypothesized that the 1st Half Blocks involve recall and reactivation of the sequence learned, thus reflecting hippocampal-dependent learning, while the 2nd Half Blocks involve proceduralized behavior of learned sequences, reflecting striatal-based learning. The present results suggest that the PD group had intact hippocampal-dependent implicit sequence learning, but impaired striatal-dependent learning. Thus, sequencing deficits in PD are likely due to striatal impairments, but other brain systems, such as the hippocampus, may be able to partially compensate for striatal decline to improve performance.

Influence of aerobic exercise training on the neural correlates of motor learning in Parkinson's disease individuals

“…The current study is the first to examine the changes in neural substrate supporting MSL following aerobic exercise training in both healthy controls and PD patients. Our findings thus extend the neuroimaging literature on implicit MSL in PD individuals and HC participants ( Gamble et al, 2014 , Ruitenberg et al, 2015 , Siegert et al, 2006 ), by specifically highlighting the positive effects of AET on the MSL-related activity in the striatum, cerebellum and; all structures that are typically involved in motor learning ( Albouy et al, 2013 , Doyon et al, 2009 , Doyon et al, 2011 ). In fact, our hypothesis regarding changes in MSL specific to striatal changes following AET was confirmed in PD individuals.…”

Physical Activity Is Associated with Reduced Implicit Learning but Enhanced Relational Memory and Executive Functioning in Young Adults

“…Second, while we found no evidence of explicit awareness here, previous studies of the TLT have included a verbal interview in addition to the computer-based recognition task [ 20 , 38 , 43 , 72 ]. Including additional measures of explicit awareness in future studies would help rule out the potential alternative interpretation that some individuals (or groups) rely on explicit strategies more than others.…”

“…However, unlike in prior sequence learning tasks, the probabilistic regularity in the TLT is very subtle and difficult to detect. In fact, explicit awareness has not been detected in this task, even in studies using multiple measures to assess awareness [ 20 , 38 , 43 , 72 ]. Further, giving participants explicit knowledge of the regularity in the ASRT, a task that is highly similar to the TLT in terms of its probabilistic structure, does not enhance their performance [ 61 ].…”

Apathy and noradrenaline

“…An initial test of sequence learning was not affected in Parkinson's disease, though patient retention a week later was [55]. Patients tested on an implicit learning sequence task performed as well as healthy controls in a first block, but not in a second block [56]. Further, no differences were found in an implicit learning task of semantic categorization between healthy controls and Parkinson's disease patients [57,58].…”