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Abstract:
We investigated the role of the basal ganglia and the
cerebellum in integrating sequential information from multiple
sources. Parkinson's disease (PD) patients, cerebellar patients,
and control participants performed a serial reaction time task in
which the stimuli followed a fixed sequence on two correlated
dimensions. In Experiment 1, a response-relevant spatial sequence
was presented with a contextual temporal sequence. In Experiment 2,
both the response-relevant and contextual dimensions were spatial.
We probed learning of each sequence separately by randomizing the
dimension of interest while maintaining the sequential presentation
of the other dimension. A phase-shift probe was used to examine
whether the sequences were integrated into a common representation.
In Experiment 1, controls learned the spatial and temporal
sequences separately and also integrated the two. Although the PD
patients learned the individual sequences, they did not exhibit
sequence integration. Cerebellar patients did not show reliable
individual or integrated sequence learning. These findings point to
a functional dissociation: The basal ganglia may be essential for
sequence integration; the cerebellum appears essential for sequence
learning, perhaps because of its role in timing. In Experiment 2,
integration was found for the control participants, but again, the
PD patients only showed significant learning for the individual
sequences. Together, the results of both experiments suggest the
basal ganglia are involved in integrating information across
multiple dimensions.
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