Parkinson Disease: Grahn JA

Grahn JA, Parkinson JA, Owen AM. · MRC Cognition and Brain Sciences Unit, Cambridge, UK. · Behav Brain Res. · Pubmed #19059285 No free full text.

Abstract: In recent years, a common approach to understanding how the basal ganglia contribute to learning and memory in humans has been to study the deficits that occur in patients with basal ganglia pathology, such as Parkinson's disease and Huntington's disease. Pharmacological manipulations in patients and in healthy volunteers have also been conducted to investigate the role of dopamine, a neurotransmitter that is crucial for normal striatal functioning. When combined with powerful functional neuroimaging methods such as positron emission tomography and functional magnetic resonance imaging, such studies can provide important new insights into striatal function and dysfunction in humans. In this review, we consider this broad literature in an attempt to define a specific role for the caudate nucleus in learning and memory, and in particular, how this role may differ from that of the putamen. We conclude that the caudate nucleus contributes to learning and memory through the excitation of correct action schemas and the selection of appropriate sub-goals based on an evaluation of action-outcomes; both processes that are fundamental to all tasks involve goal-directed action.

Grahn JA, Brett M. · MRC Cognition and Brain Sciences Unit, Cambridge, UK. · Cortex. · Pubmed #19027895 No free full text.

Abstract: Humans often synchronize movements to the beat, indicating that motor areas may be involved in detecting or generating a beat. The basal ganglia have been shown to be preferentially activated by perception of rhythms with a regular beat (Grahn and Brett, 2007), but their necessity for beat-based rhythm processing has not been proven. Previous research has shown that Parkinson's disease (PD) patients are impaired in timing of isochronous intervals (Harrington et al., 1998a; O'Boyle et al., 1996), but little work has tested more complex rhythms. In healthy volunteers, behavioural performance is better for rhythms with a beat than without a beat (Essens, 1986). We tested PD patients and controls on a rhythm discrimination task to determine if basal ganglia dysfunction results in an impairment of processing rhythms that have a beat. Unlike rhythm reproduction, discrimination has no motor requirements that are problematic for patients. Half the rhythms had a beat-based structure, and half did not. Subjects heard a rhythm twice and then indicated if a third presentation of the rhythm was the same or different. We predicted that PD patients would benefit less from beat structure than controls, resulting in a group by rhythm-type interaction, with reduced relative performance for the beat-based sequences in the PD group. Indeed this was the pattern of the results. In the control group, a significant advantage was observed for discrimination of rhythms with a beat compared to those without a beat. This advantage was greatly reduced in the PD group. Discrimination of beat-based rhythms was significantly impaired in PD patients compared to controls, whereas discrimination of non-beat-based rhythms did not differ significantly. This suggests that the basal ganglia are part of a system involved in detecting or generating an internal beat, and that this system is compromised in patients with Parkinson's disease.