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Abstract Details

Abnormal intracortical facilitatory-inhibitory circuit interactions in patients with Parkinson’s disease
Movement Disorders
P4 - Poster Session 4 (5:30 PM-6:30 PM)
3-009

To determine the interactions between inhibitory and facilitatory intracortical circuits in Parkinson’s disease (PD).

Using transcranial magnetic stimulation (TMS), previous work has established that motor cortical inhibitory and facilitatory circuits are abnormal in patients with PD. Three such circuits are short interval intracortical inhibition (SICI), short interval intracortical facilitation (SICF) and short-latency afferent inhibition (SAI). They assess GABAAergic, glutamatergic and cholinergic function, respectively. Importantly, these circuits interact with each other and their interactions can be tested using a triple-pulse TMS paradigm, which elicits one circuit in the presence of another. However, these interactions have not been studied in PD.
15 right-handed PD patients (aged 64.8±7.9 years) were studied ON and OFF dopaminergic medications. Unified Parkinson’s Disease Rating Scale Part III (UPDRS-III) was used to assess disease severity. 16 right-handed, healthy participants (aged 64.1±6.9 years) served as controls. Surface electromyography measured motor evoked potentials from the first dorsal interosseous muscle generated by TMS of left motor cortex (M1) in controls and of M1 in the more affected hemisphere in PD patients. SICI was tested at an interstimulus interval (ISI) of 2 ms and SICF at an ISI of 1.5 ms. The latency of the median nerve N20 somatosensory evoked potential plus 2 ms was used as the ISI for SAI. 

SICF was increased in PD OFF and PD ON conditions compared to controls. SICI facilitated SICF in controls and PD ON, but not in PD OFF. SICF in the presence of SICI negatively correlated with UPDRS-III scores in OFF and ON medication conditions. SAI showed similar inhibition of SICI in controls, PD OFF and PD ON conditions.

Facilitation of SICF by SICI is impaired in PD and is corrected by dopaminergic medications. Altered interactions between motor cortical circuits contribute to the pathophysiology of PD.
Authors/Disclosures

PRESENTER 		No disclosure on file
No disclosure on file
Kaviraja Udupa, MD, PhD (University Health Network Toronto) No disclosure on file
No disclosure on file
Julianne Baarbé No disclosure on file
Robert E. Chen, MD, MBBChir (Toronto Western Hospital) Dr. Chen has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Abbvie. Dr. Chen has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Merz. Dr. Chen has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Ipsen. Dr. Chen has received personal compensation in the range of $10,000-$49,999 for serving as an Editor, Associate Editor, or Editorial Advisory Board Member for International Federation of Clinical Neurophysiology. Dr. Chen has received personal compensation in the range of $500-$4,999 for serving as an Editor, Associate Editor, or Editorial Advisory Board Member for Movement Disorders. The institution of Dr. Chen has received research support from Canadian Institutes of Health Research. The institution of Dr. Chen has received research support from Natural Science and Engineering Research Council of Canada. Dr. Chen has received research support from Parkinson Foundation. The institution of Dr. Chen has received research support from National Organization for Rare Disease. The institution of Dr. Chen has received research support from Abbvie.