Distinct alterations in Parkinson's Medication-state and Disease-state Connectivity Running Title: PD altered connectivity
Résumé
Altered brain connectivity has been described in people with Parkinson’s disease and in response
to dopaminergic medications. However, it is unclear whether dopaminergic medications
primarily ‘normalize’ disease related connectivity changes or if they induce unique alterations in
brain connectivity. Further, it is unclear how these disease- and medication- associated changes
in brain connectivity relate differently to specific motor manifestations of disease, such as
bradykinesia/rigidity and tremor. In this study, we applied a novel covariance projection
approach in combination with a bootstrapped permutation test to resting state functional MRI
data from 57 Parkinson’s disease and 20 healthy control participants to determine the
Parkinson’s medication-state and disease-state connectivity changes associated with different
motor manifestations of disease. First, we identified brain connections that best classified
Parkinson’s disease ON versus OFF dopamine and Parkinson’s disease versus healthy controls,
achieving 96.9 ± 5.9% and 72.7 ± 12.4% classification accuracy, respectively. Second, we
investigated the connections that significantly contribute to the classifications. We found that the
connections greater in Parkinson’s disease OFF compared to ON dopamine are primarily
between motor (cerebellum and putamen) and posterior cortical regions, such as the posterior
cingulate cortex. By contrast, connections that are greater in ON compared to OFF dopamine are
between the right and left medial prefrontal cortex. We also identified the connections that are
greater in healthy control compared to Parkinson’s disease and found the most significant
connections are associated with primary motor regions, such as the striatum and the
supplementary motor area. Notably, these are different connections than those identified in
Parkinson’s disease OFF compared to ON. Third, we determined which of the Parkinson’s
medication-state and disease-state connections are associated with the severity of different motor
symptoms. We found two connections correlate with both bradykinesia/rigidity severity and
tremor severity, whereas four connections correlate with only bradykinesia/rigidity severity, and
five connections correlate with only tremor severity. Connections that correlate with only tremor
severity are anchored by the cerebellum and the supplemental motor area, but only those
connections that include the supplemental motor area predict dopaminergic improvement in
tremor. Our results suggest that dopaminergic medications do not simply ‘normalize’ abnormal
brain connectivity associated with Parkinson’s disease, but rather dopamine drives distinct
connectivity changes, only some of which are associated with improved motor symptoms. In
addition, the dissociation between of connections related to severity of bradykinesia/rigidity
versus tremor highlights the distinct abnormalities in brain circuitry underlying these specific
motor symptoms.
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