How does the brain respond to unimodal and bimodal sensory demand in movement of the lower extremity?

Numerous electroencephalography (EEG) studies have shown that neurophysiological signals change in response to visual and sensory adaptations in upper extremity tasks. However, this has not been clearly studied in the lower extremity. In this study, we evaluated how sensory loading affects brain activations related to knee movement. Thirty-two channel EEG was recorded while ten subjects performed knee extension in four different conditions: no weight and no visual target (NWNT), weight affixed to the ankle and no visual target (WNT), no weight and a visual target (NWT), and both weight and target (WT). Surface electromyography (EMG) was recorded from the vastus medialis and vastus lateralis muscles to determine onset of the movement. EEG was epoched from -4.5 s before to 1 s after EMG onset. Epochs were averaged to acquire movement-related cortical potentials (MRCPs) of each task condition. MRCP amplitude during the pre-movement period from -2 s to EMG onset was evaluated at electrodes over motor, sensory, frontal, and parietal areas. The amplitude of the pre-movement potentials for the conditions was different across areas of interest. Over the motor area, NWNT had lower amplitude than any other condition and WT had higher amplitude than any other condition. There was no difference between unimodal NWT and WNT conditions. Mesial frontal and parietal areas showed larger MRCP to the bimodal condition than either unimodal or NWNT conditions. The parietal cortex was the only region that showed a difference between unimodal conditions with greater amplitude for NWT condition. Information concerning added sensory demand is processed by the motor cortex in a way that may be indifferent to the type of modality, but is influenced by the quantity of modalities at the level of the knee. Other brain structures such as parietal and premotor cortices respond based on the modality type to help plan appropriate strategies for motor control in response to sensory manipulations. This suggests that additional task demands in motor training may create a rich sensory environment that may be beneficial in promoting optimal neuromotor recovery.