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

Abstract

We investigated the effects of different patterns of mechanical tactile stimulation (MS) on corticospinal excitability by measuring the motor-evoked potential (MEP). This was a single-blind study that included nineteen healthy subjects. MS was applied for 20 min to the right index finger. MS intervention was defined as simple, lateral, rubbing, vertical, or random. Simple intervention stimulated the entire finger pad at the same time. Lateral intervention stimulated with moving between left and right on the finger pad. Rubbing intervention stimulated with moving the stimulus probe, fixed by protrusion pins. Vertical intervention stimulated with moving in the forward and backward directions on the finger pad. Random intervention stimulated to finger pad with either row protrudes. MEPs were measured in the first dorsal interosseous muscle to transcranial magnetic stimulation of the left motor cortex before, immediately after, and 5-20 min after intervention. Following simple intervention, MEP amplitudes were significantly smaller than preintervention, indicating depression of corticospinal excitability. Following lateral, rubbing, and vertical intervention, MEP amplitudes were significantly larger than preintervention, indicating facilitation of corticospinal excitability. The modulation of corticospinal excitability depends on MS patterns. These results contribute to knowledge regarding the use of MS as a neurorehabilitation tool to neurological disorder.

Figure 1

The settings of mechanical tactile stimulation. The mechanical tactile stimulator comprised 24 tiny plastic pins driven by piezoelectric actuators. A mechanical tactile stimulation was applied to the tip of the right index finger.

Figure 2

The condition of intervention (black dot: tactile-off, white dot: tactile-on). Five interventions (a–e) were applied for 20 min (stim on/stim off: 1 s/5 s).

Figure 3

Experimental protocol. Motor-evoked potential as a measure of corticospinal excitability was measured before the intervention (preintervention), immediately after intervention (immediately), and 5 (post 5 min), 10 (post 10 min), 15 (post 15 min), and 20 min after the intervention (post 20 min). Transcranial magnetic stimulation was delivered in 15 trials at 0.2 Hz. The interventions performed in a repeated measurement design using a randomized order, with an interval of at least 1 week between each condition.

Figure 4

The motor-evoked potential (MEP) amplitude of each subject and the mean before and after interventions (black line: mean data, gray line: each subject data). (a) The mean MEP amplitudes were significantly smaller immediately 5 min and 10 min after simple intervention than they were preintervention (immediately; P = 0.006, post 5 min; P < 0.001, post 10 min; P = 0.004). (b) The mean MEP amplitudes were significantly larger 5 min and 10 min after lateral complex intervention than they were preintervention (post 5 min; P = 0.016, post 10 min; P = 0.013). (c) The mean MEP amplitudes were significantly larger 5 min and 10 min after rubbing intervention than they were preintervention (post 5 min; P = 0.024, post 10 min; P = 0.004). (d) The mean MEP amplitudes were significantly larger 5 and 10 min after vertical complex intervention than they were preintervention (post 5 min; P = 0.024, post 10 min; P = 0.003). (e) The mean MEP amplitudes were not significantly different between prerandom complex intervention and postintervention. (^∗; P < 0.05, ^∗∗; P < 0.01).