Is the Brain's Inertia for Motor Movements Different for Acceleration and Deceleration?

Bhim M Adhikari,Kristen M Quinn,Mukesh Dhamala

doi:10.1371/journal.pone.0078055

Abstract

The brain's ability to synchronize movements with external cues is used daily, yet neuroscience is far from a full understanding of the brain mechanisms that facilitate and set behavioral limits on these sequential performances. This functional magnetic resonance imaging (fMRI) study was designed to help understand the neural basis of behavioral performance differences on a synchronizing movement task during increasing (acceleration) and decreasing (deceleration) metronome rates. In the MRI scanner, subjects were instructed to tap their right index finger on a response box in synchrony to visual cues presented on a display screen. The tapping rate varied either continuously or in discrete steps ranging from 0.5 Hz to 3 Hz. Subjects were able to synchronize better during continuously accelerating rhythms than in continuously or discretely decelerating rhythms. The fMRI data revealed that the precuneus was activated more during continuous deceleration than during acceleration with the hysteresis effect significant at rhythm rates above 1 Hz. From the behavioral data, two performance measures, tapping rate and synchrony index, were derived to further analyze the relative brain activity during acceleration and deceleration of rhythms. Tapping rate was associated with a greater brain activity during deceleration in the cerebellum, superior temporal gyrus and parahippocampal gyrus. Synchrony index was associated with a greater activity during the continuous acceleration phase than during the continuous deceleration or discrete acceleration phases in a distributed network of regions including the prefrontal cortex and precuneus. These results indicate that the brain's inertia for movement is different for acceleration and deceleration, which may have implications in understanding the origin of our perceptual and behavioral limits.

Highlights

Rhythm is an essential part of our daily lives as almost all common activities require an element of timing
By using the average synchrony index as defined above, we found that there was a significantly higher synchrony index for increasing rates of rhythms than for decreasing rhythms in continuous sinusoidal variation for all subjects [Fig. 3 (A) and 3 (C)]
These behavioral results are consistent with what subjects reported in their post-task response: that deceleration was more difficult than acceleration in the continuous case and that the discrete case was more difficult than the continuous case

Summary

Introduction

Rhythm is an essential part of our daily lives as almost all common activities require an element of timing. The coordination of rhythmic movement with an external rhythm is called sensorimotor synchronization (SMS) [1]. This study aims to shed light on how the brain achieves its precise timing, is it more difficult to achieve SMS with accelerating or decelerating rhythms, and what neuronal features set the behavioral limits on the speed and accuracy of SMS. Answers to these questions will have implications for understanding the origin of the brain’s cognitive ‘inertia’, and for rehabilitation efforts in movement disorders including Parkinson’s disease, Huntington’s disease and traumatic brain injury

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