Touch automatically upregulates motor readiness in humans

Abstract

van Ede F, Winner T, Maris E. Touch automatically upregulates motor readiness in humans. J Neurophysiol 114: 3121-3130, 2015. First published September 23, 2015 doi:10.1152/jn.00504.2015.-Goal-directed movements require effective integration of tactile input with ongoing movement. Here we investigated the functional consequences of such integration in healthy humans by probing the influence of spatially congruent and incongruent tactile stimuli on performance in a speeded button-press task. In addition, using magnetoencephalography (MEG), we evaluated whether the modulation of somato-motor beta (13-30 Hz) oscillations following tactile inputwhich has been shown to propagate to motor areas-could underlie this influence. We demonstrate that congruent tactile stimuli, despite being irrelevant to the motor task, lead to both faster and more accurate responses. We further show that this automatic upregulation of lateralized motor readiness 1) is specific to tactile input, 2) is independent of the spatial separation of the hands in peripersonal space, and 3) lasts (and remains facilitatory) for up to a second after the tactile input. This pattern of behavioral results is in line with recent physiological investigations showing that somatosensory and motor areas directly influence each other's processing capacity through joint changes in brain state. At the same time, however, the tactile-induced modulation of beta oscillations (one particular index of such a somatomotor state change) could not account for the observed movement facilitation, because it had a different time course. tactile stimuli; movement; sensorimotor integration; beta oscillations; automatic facilitation GOAL-DIRECTED MOVEMENTS require effective interactions between the brain's somatosensory and motor areas. Recent physiological studies have suggested that such interactions are facilitated by the direct influence of somatosensory areas on motor areas, and vice versa. For example, stimulation of rodent primary motor cortex (M1) influences the physiological state of the primary somatosensory cortex (S1) through a direct pathway from M1 to S1, and this improves sensory processing (Lee et al. 2013;Zagha et al. 2013). Likewise, sensory responses and state changes in S1 propagate to M1 (Ferezou et al. 2007) as well as the spinal cord (van Ede and Maris 2013) and may even contribute to motor control directly (Coulter and Jones 1977;Matyas et al. 2010). To date, however, the behavioral consequences of such tactile-induced state changes of the motor system have remained largely unexplored. Moreover, most previous inferences on the integration between touch and movement (including the involvement of somato-motor state changes) have been based on animal (i.e., rodent) models. In the present work, we therefore aimed at characterizing the influence of touch on movement in healthy humans. In particular, we investigated the influence of external tactile stimuli on motor readiness: the ability to respond quickly to an arbitrary response signal (imperative cue).Our...

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