Neurostimulation in tactile perception

Neurostimulation techniques are used to study the healthy human central and peripheral nervous system non-invasively by stimulating neural tissue magnetically or electrically. Such approaches have been successfully applied to study the motor system as well as several other brain systems. This chapter will focus on stimulation of the somatosensory system. Typically, neurostimulation is applied to a certain brain area by positioning a coil (e.g., in transcranial magnetic stimulation, TMS) or an electrode (e.g., transcranial electrical stimulation, TES) on the scalp location over the brain area of interest. When primary motor cortex (M1) is stimulated with TMS, motor-evoked potentials (MEPs) and twitches are observed in the targeted muscles of the body. However, unlike over M1, stimulation to somatosensory and other cortices does not produce immediately observable outputs. This introduces problems of localization and other challenges, such as the optimal experimental designs and behavioral tasks, when using neurostimulation to study tactile perception. This chapter will describe and evaluate these approaches. Practical and participant-specific difficulties will be noted. Neurostimulation methods offer relatively cheap and reliable means of modulating somatosensation, yet care is required to ensure that the experimental design is adequate, that the optimal location is stimulated, and that the data are able to answer your theoretical question.