Several studies have shown that a light fingertip touch on a stable surface reduces body sway for individuals standing with their eyes closed even when touch forces are too low to offer mechanical support. It has been proposed that this is due to the availability of sway-relevant sensory feedback from the hand compensating for lost vision. Recently, we revealed modulation of cortical sensory transmission of information from the hand depending on the task (e.g. relevant or not relevant to balance control). Of interest in the present study is the potential origin of task-specific modulation of cortically evoked sensory potentials linked to balance control. We aimed to investigate the role of the prefrontal cortex by temporarily suppressing this region and observing differences in cortical events. Continuous è-burst stimulation was applied to either the prefrontal cortex or a control stimulation site before balance testing. During balance testing, individuals stood in tandem on a force plate with their eyes closed while lightly touching a stable surface or a sway-referenced surface with the index finger. Throughout testing, the median nerve was stimulated and electroencephalography was used to measure somatosensory-evoked potentials. As expected, the availability of stable light touch reduced the medial-lateral centre of pressure sway. Importantly, in the present study, there was a loss of task-related P200 modulation at FCZ following stimulation of the prefrontal cortex. The present findings support the hypothesis that the prefrontal cortex may serve to regulate task-related sensory reweighting of haptic information that may be used during the control of standing balance.
Adult Electroencephalography