Determining the number of stimuli required to reliably assess corticomotor excitability and primary motor cortical representations using transcranial magnetic stimulation (TMS): A protocol for a systematic review and meta-analysis

Abstract

Background: Transcranial magnetic stimulation (TMS) is a technique that can be used to assess corticospinal plasticity. Current TMS practices involve the administration of multiple stimuli over target areas of the participant's scalp. However, these procedures require 1 to 2 h per assessment. Decreasing the number of stimuli delivered during TMS assessments would improve time efficiency and decrease participant demand. Thus, the aim of this review is to determine the number of TMS stimuli required to reliably measure (1) corticomotor excitability to a target muscle at a single cranial site and (2) the topography of the primary motor cortical representation for a target muscle across multiple cranial sites (termed 'mapping'). Methods/design: A systematic review and meta-analysis will be conducted. Electronic databases will be searched using pre-determined search terms to identify relevant studies and evaluate the studies for inclusion and risks of bias. Two independent reviewers will extract the data. Any disagreements will be resolved by a third reviewer. Studies employing single-pulse TMS to measure (1) corticomotor excitability at a single cranial site or (2) the topographic cortical organisation of a target muscle across a number of cranial sites, published before May 2015, will be included if they meet the eligibility criteria. Outcomes will include motor-evoked potential amplitude, map volume, number of active map sites, location of the map centre of gravity, and distance between the centres of gravity of the target muscle and one or more neighbouring muscles. Discussion: To our knowledge, this review will be the first to systematically explore the number of TMS stimuli required to reliably measure both corticomotor excitability and the topography of primary motor cortical representations. This research has the capacity to improve the efficiency of TMS, decrease participant demand, and facilitate the use of TMS as an outcome measurement tool in clinical populations. Systematic review registration: PROSPERO CRD42015024579.