Post-stimulus beta responses are modulated by task duration

Daisie O Pakenham,Andrew J Quinn,Adam Fry,Susan T Francis,Mark W Woolrich,Matthew J Brookes,Karen J Mullinger

doi:10.1016/j.neuroimage.2019.116288

Abstract

Modulation of beta-band neural oscillations during and following movement is a robust marker of brain function. In particular, the post-movement beta rebound (PMBR), which occurs on movement cessation, has been related to inhibition and connectivity in the healthy brain, and is perturbed in disease. However, to realise the potential of the PMBR as a biomarker, its modulation by task parameters must be characterised and its functional role determined. Here, we used MEG to image brain electrophysiology during and after a grip-force task, with the aim to characterise how task duration, in the form of an isometric contraction, modulates beta responses. Fourteen participants exerted a 30% maximum voluntary grip-force for 2, 5 and 10 s. Our results showed that the amplitude of the PMBR is modulated by task duration, with increasing duration significantly reducing PMBR amplitude and increasing its time-to-peak. No variation in the amplitude of the movement related beta decrease (MRBD) with task duration was observed. To gain insight into what may underlie these trial-averaged results, we used a Hidden Markov Model to identify the individual trial dynamics of a brain network encompassing bilateral sensorimotor areas. The rapidly evolving dynamics of this network demonstrated similar variation with task parameters to the ‘classical’ rebound, and we show that the modulation of the PMBR can be well-described in terms of increased frequency of beta events on a millisecond timescale rather than modulation of beta amplitude during this time period. Our results add to the emerging picture that, in the case of a carefully controlled paradigm, beta modulation can be systematically controlled by task parameters and such control can reveal new information as to the processes that generate the average beta timecourse. These findings will support design of clinically relevant paradigms and analysis pipelines in future use of the PMBR as a marker of neuropathology.

Highlights

Motor tasks typically generate electrophysiological responses in the beta (15–30 Hz) frequency band (Jurkiewicz et al, 2006). Such responses comprise a decrease in amplitude during movement - the movement related beta decrease (MRBD) - followed by an increase in amplitude above baseline on movement cessation - the post-movement beta rebound (PMBR)
Though the PMBR and MRBD are sustained over several seconds in the time frequency spectrograms (TFSs) responses, the Hidden Markov Model (HMM) analysis shows that the average motor beta event underlying these effects are only around 100 ms
We showed from the HMM analyses that the length of each visit to the “rebound” state is greatest in the PMBR period (79Æ7 ms) and least during the MRBD (55Æ6 ms) (Fig. 6Dii)

Summary

Introduction

Motor tasks typically generate electrophysiological responses in the beta (15–30 Hz) frequency band (Jurkiewicz et al, 2006) Such responses comprise a decrease in amplitude during movement - the movement related beta decrease (MRBD) - followed by an increase in amplitude above baseline on movement cessation - the post-movement beta rebound (PMBR). During movement itself, the MRBD has been shown to be relatively unaffected by parameters such as force output, rate of force development (Fry et al, 2016), or speed of force development (Stancak and Pfurtscheller, 1995, 1996) This has led to a hypothesis that the MRBD relates to movement planning and execution, but not to measurable changes in peripheral output

Methods

Results

Discussion

Conclusion