Attentional modulation of the somatosensory mu rhythm.

Neural oscillations with a frequency of around 10 Hz are thought to be a ubiquitous phenomenon in sensory cortices, and it has been hypothesized that the level of 10 Hz activity is related to local cortical excitability. During spatial attention, the visual alpha rhythm has been found to be modulated according to the direction of attention. Specifically, the alpha rhythm desynchronizes over visual cortex contralateral to the direction of attention and synchronizes over visual cortex ipsilateral to the direction of attention, and these modulations have been associated with facilitation and inhibition of sensory processing. In the somatosensory domain, the reactivity of a similar rhythm, known as the mu rhythm, during attention tasks is a current topic of inquiry and somatotopic modulation of the mu rhythm by directed attention have been reported. In this paper, we investigate how lateralized spatial attention modulates the ongoing somatosensory mu rhythm, and how such modulation impacts sensory information processing. 128 channel EEG was recorded while subjects performed a somatosensory spatial attention task. In addition to analyses on scalp recorded data, a spatial filtering method was utilized to investigate spatial attention effects in the source space. The direction of spatial attention was found to have a significant somatotopic effect on the ongoing mu rhythm occurring in primary somatosensory cortex. Concurrently, the visual alpha rhythm was significantly elevated above the baseline level during somatosensory attention, demonstrating a cross-modal effect. Lastly, an analysis was performed to investigate the correlation between the level of prestimulus mu activity and subsequent stimulus evoked activity in primary somatosensory cortex.