Selective increase in corticospinal excitability in the context of tactile exploration

Abstract

In this study, we compared changes in corticomotor excitability under various task conditions engaging the index finger of each hand. Functional demands were varied, from simple execution to demanding sensory exploration. In a first experiment, we contrasted facilitation in the first dorsal interosseus (FDI) by monitoring changes in motor evoked potentials (MEPs) when participants (young adults, n = 18) performed either a simple button pressing (BP) task or a more demanding tactile exploration (TE) task (i.e., discrimination of raised letters). This experiment showed a large effect of task conditions (p < 0.01) on MEP amplitude but no effect of "Hand", while latency measurements were unchanged. In fact, MEPs were on average 40% larger during TE (2410 +/- 1358 microV) than during BP (1670 +/- 1477 microV). The two tasks produced, however, different patterns of electromyographic (EMG) activity, which could have accounted for some of the differences observed. A second experimental session involved a subset of participants (10/18) tested in third task condition: finger movement (FM). The latter task consisted of scanning a smooth surface with the tip of the index finger to reproduce the movements seen with the TE task. The addition of this third condition task confirmed that MEP facilitation seen during TE reflected task-specific influences and not differences in background EMG activity. These results, altogether, provide further insights into the effect of task conditions on corticomotor excitability. Our findings, in particular, stress the importance of behavioural context and tactile exploration in leading to selective increase in corticomotor excitability during finger movements.

Modulation of Corticospinal Excitability Depends on the Pattern of Mechanical Tactile Stimulation

“…Somatosensory input is a widely used intervention in rehabilitation of neurological disorders such as strokes [ 1 , 2 ]. This is because studies suggest that sustained somatosensory inputs such as electrical stimulation [ 3 – 10 ], vibration [ 11 , 12 ], whole-hand water flow [ 13 ], and tactile stimulation [ 14 ] modulate cortical and corticospinal excitability. For example, motor-evoked potential (MEP), which indicates corticospinal excitability, was increased for 15 min following electrical stimulation of ulnar nerve for 2 h [ 3 ].…”

Task-related enhancement in corticomotor excitability during haptic sensing with the contra- or ipsilateral hand in young and senior adults

“…In a recent series of experiments, we have investigated with TMS the neurophysiological correlates of motor cortical activation associated with unimanual performance using various forms of haptic sensing tasks [8-11]. Haptic sensing with the fingers represents a unique class of manipulative actions, engaging motor, somatosensory and associative areas of the cortex while requiring only minimal forces and relatively simple movement patterns [12,13].…”

Effects and after-effects of voluntary intermittent light finger touch on body sway

“…This means that any subsequent trains of touch durations shorter than 5 s, interrupting the no touch periods of 6-s duration, were not considered sufficiently informative in terms of touch feedback utilization and thus did not suggest sustained sensory gain settings. It is also possible that continuous tactile exploration, e.g., 5-s continuous light touch, leads to enhanced cortical excitability [24], and hence its touch effects may last after touch withdrawal during which the enhanced cortical excitability is still maintained. Another mechanism that may account for the after-effects is the constraining effect brought about by the suprapostural touch task.…”