Demonstrating the need for long inter-stimulus intervals when studying the post-movement beta rebound following a simple button press

Voluntary movements reliably elicit event-related synchronization of oscillatory neuronal rhythms in the beta (15-30 Hz) range immediately following movement offset, as measured by magneto/electroencephalography (M/EEG). This response has been termed the post-movement beta rebound (PMBR). While early work on the PMBR advocated for long inter-stimulus intervals (ISIs)--arguing that the PMBR might persist for several seconds--these concerns have since fallen by the wayside, with many recent studies employing very short (< 5 s) ISIs. In this work we interrogated sensor-level MEG time courses in 635 individuals who participated in a cued button- pressing paradigm as part of the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) project. We focussed on a subset of trials in which button presses were separated by at least 15 seconds and, using curve modelling and Bayesian inference, estimated the point at which beta power returned to baseline levels. We show that beta power takes around 4-5 seconds to return to baseline levels following movement. These results have important implications for experimental design. The PMBR is ubiquitously defined relative to a preceding baseline period; we argue that short ISIs preclude true baseline estimation and, in turn, accurate estimation of PMBR magnitude. We recommend that future studies targeting the PMBR use ISIs of at least 7 seconds--5 seconds for beta power to return to baseline, plus a 1-2 second period for proper baseline estimation. Further work is needed to clarify PMBR duration in the context of different sensorimotor paradigms and clinical populations.