Assessing cortical involvement in stretch reflex response using subthreshold TMS

In movement control cortical signals are integrated with afferent feedback from reflexes. Disturbed integration is suggested to underlie many movement disorders. Cortical and afferent signals can integrate in the spinal cord and at supraspinal centres, though the exact location and mechanism of integration are unknown yet. The goal of this study is to assess the cortical involvement during the stretch reflex response. Mechanically induced stretches of the muscle flexor carpi radialis where combined with subthreshold transcranial magnetic stimulation (TMS, 97% of active motor threshold) at interstimulus intervals ranging from 35 to 80 ms. Muscle response was measured using high-density electromyography (EMG), providing additional spatial muscle activation patterns. Magnitude of resulting EMG reflex activity, i.e. short (M1, 20-50 ms) and long (M2, 55-100 ms) latency reflex responses were compared to stretch-only trials. Subthreshold TMS was found to significantly increase the stretch evoked EMG response (p < 0.001) when TMS pulses were timed to arrive at the muscle in the time window of the M2 response. Absence of facilitation of the spinally mediated M1 response indicates that integration of cortical and afferent feedback signals in M2 occurs at a supraspinal level. Spatial muscle activation patterns of suprathreshold TMS were consistent over trials, while spatial patterns due to stretch reflexes were less consistent. Spatial patterns of combined trials are therefore not conclusive about the mechanism of integration.

Subject

stretch reflex
transcranial magnetic stimulation
high density electromyography

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http://resolver.tudelft.nl/uuid:65b2ac69-bb10-44e7-bf2f-fbd729e517eb

Embargo date

2014-01-17

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Student theses

Document type

master thesis

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Thesis_Thijs_Perenboom.pdf

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