The Relationship Between Cortical Hyperexcitability and Loss of Primary Motor Cortex Excitability in those Predisposed to Aberrant Experiences following Upper Limb Immobilisation : An Exploration

Joshi, Shalmali and Robinson, Abbie and Drinkwater, Amber and O'Hanlon, Brandon and Gaffney, Christopher and Nuttall, Helen E and Braithwaite, J. J. (2024) The Relationship Between Cortical Hyperexcitability and Loss of Primary Motor Cortex Excitability in those Predisposed to Aberrant Experiences following Upper Limb Immobilisation : An Exploration. PsyArXiv.

Abstract

Multi-sensory integration is a core aspect of stable self-awareness however it known that this has a propensity to breakdown leading to aberrant experiences (such as hallucinations, distortions, aberrant body experiences). Limb immobilisation has been associated with decrease in corticomotor efficiency and atypical multi-sensory integration. The present study explored the role of predisposition to aberrant experiences and depersonalisation-like experiences in maintaining corticomotor efficiency by rTMS stimulation. Twelve healthy participants were recruited to participate in a limb immobilisation within-subject paradigm. All participants completed two trait-based measures (relating to aberrant experiences and depersonalisation experiences and a state-based measure (where skin conductance responses were measured to a fake blood-giving procedure) indexing interoceptive vulnerability. Cortical excitability was measured by motor evoked potential (MEP) responses to single-pulse TMS in a stepwise procedure for each day of immobilisation. Participants were then randomised into a treatment group (n = 6) who received six 1.5 seconds 50 Hz repetitive inter-pulse trains at 60s intervals and a sham group (n = 6) per day of immobilisation. The results indicated that although the stimulation paradigm was successful in increasing cortical excitability initially, these effects were not maintained throughout the immobilisation period and MEPs evidenced a continual decrease in amplitude over time. Stratification of the participants based on trait-based and state-based measures did not produce any reliable findings. Taken together, this indicated that the stimulation paradigm in isolation was insufficient in maintaining cortical excitability and that baseline brain states are an important consideration for future alternative therapeutic paradigms. Theoretical and methodological improvements are discussed.