Exploring EEG Microstates During Motor Movements: A Study on Tip-pinch and Wrist flexion & extension

Abstract

The electroencephalography (EEG) technique measures scalp electrical activity with high temporal resolution; required to map the neuronal global functional brain networks supporting motor movements. The time series of the change in electric potential across electrodes is analysed using frequency (and/or) time domain methods. An alternate approach is to represent a dynamic system with states and transitions between them defined using microstates. These are quasi-stable (60-120 ms) scalp potential configurations that represent spontaneous EEG as a sequence of a small number of scalp potential field maps and provide insight into brain health exhibiting sub-second coherent activations of brain. The present study investigates microstates extracted from EEG signals of motor-tasks. We investigate the extracted microstate parameters (occurrence, duration, coverage and no. of microstate) for Tip-pinch movement (index finger & thumb) and Wrist flexion & extension performed by both hands independently. These movements are selected due to its relevance in benchmarking rehabilitation of paretic arm post-stroke. The data was extracted from 17 electrodes (of a 32 channel EEG system) covering the pre-frontal, frontal, central and motor regions. Twenty-four right-handed and five left-handed healthy male subjects (age = 18-30 years; mean = 24.25 years; SD = 3.96 years) participate in this study. The approach of analysing each dynamic variable (occurrence, duration, coverage, and number of microstate) values during pre-event, event, and post-event conditions with reported resting state microstates highlights the similarities or differences as a function of motor action. We identified new microstate topographies specific to each motor task. The number of microstates for both motor activities is independent of the handedness of the participant (right-handed and left-handed). Task dependent variation in the topography of the microstates is observed, deviating from the standard maps reported for resting state EEG. The tip-pinch movement for event condition demonstrates higher microstate class stability than Wrist flexion & extension, indicative of lower disruption in the processing for the former action. The identification of disruptions or novel topologies for a task indicates the potential to function as a physiological marker, even considering the arguments on microstate’s state change being discrete or continuous. The findings will serve as a template for future studies analysing data from stroke patients.