Mana Higashihara1, Mehdi A J Van den Bos1, Parvathi Menon1, Matthew C Kiernan2, Steve Vucic3. 1. Westmead Clinical School, University of Sydney, Australia. 2. Brain and Mind Center, University of Sydney, Australia. 3. Westmead Clinical School, University of Sydney, Australia. Electronic address: steve.vucic@sydney.edu.au.
Abstract
OBJECTIVE: Recruitment of interneuronal circuits generating later indirect (I) waves seem to be important in short-interval intracortical inhibition (SICI) and facilitation (SICF) development. This study assessed whether individual variations in intracortical inhibition and facilitation could be explained by variation in recruitment of interneuronal networks. METHODS: Cortical excitability was assessed using a figure of eight coil, with motor evoked responses recorded over the contralateral abductor pollicis brevis (APB) muscle. I-wave recruitment was inferred from the measurement of motor evoked potential (MEP) onset latencies, with coil positioned in posterior-to-anterior (early I waves) and anterior-to-posterior (later I waves) directions. RESULTS: Subtle variability in the recruitment of later I-waves (I3) was evident across subjects. Importantly, mean SICI (P < 0.05) was significantly greater in subjects recruiting I3 waves, as were the two SICI peaks at interstimulus intervals of 1 ms (P < 0.05) and 3 ms (P < 0.05). In addition, mean SICF was significantly greater in participants exhibiting an AP-to-LM latency differences of <4 ms (P < 0.01). There was no significant correlation between I-wave recruitment and intracortical facilitation, motor evoked potential amplitude or cortical silent period duration. CONCLUSIONS: Differential recruitment of interneuronal networks appears to underlie the generation and individual variations in intracortical inhibition and facilitation. SIGNIFICANCE: Investigating cortical interneuronal networks in human diseases may yield novel pathophysiological insights.
OBJECTIVE: Recruitment of interneuronal circuits generating later indirect (I) waves seem to be important in short-interval intracortical inhibition (SICI) and facilitation (SICF) development. This study assessed whether individual variations in intracortical inhibition and facilitation could be explained by variation in recruitment of interneuronal networks. METHODS: Cortical excitability was assessed using a figure of eight coil, with motor evoked responses recorded over the contralateral abductor pollicis brevis (APB) muscle. I-wave recruitment was inferred from the measurement of motor evoked potential (MEP) onset latencies, with coil positioned in posterior-to-anterior (early I waves) and anterior-to-posterior (later I waves) directions. RESULTS: Subtle variability in the recruitment of later I-waves (I3) was evident across subjects. Importantly, mean SICI (P < 0.05) was significantly greater in subjects recruiting I3 waves, as were the two SICI peaks at interstimulus intervals of 1 ms (P < 0.05) and 3 ms (P < 0.05). In addition, mean SICF was significantly greater in participants exhibiting an AP-to-LM latency differences of <4 ms (P < 0.01). There was no significant correlation between I-wave recruitment and intracortical facilitation, motor evoked potential amplitude or cortical silent period duration. CONCLUSIONS: Differential recruitment of interneuronal networks appears to underlie the generation and individual variations in intracortical inhibition and facilitation. SIGNIFICANCE: Investigating cortical interneuronal networks in human diseases may yield novel pathophysiological insights.
Authors: Andris Cerins; Daniel Corp; George Opie; Michael Do; Bridgette Speranza; Jason He; Pamela Barhoun; Ian Fuelscher; Peter Enticott; Christian Hyde Journal: Sci Rep Date: 2022-06-15 Impact factor: 4.996