Difference in somatosensory evoked fields elicited by mechanical and electrical stimulations: Elucidation of the human homunculus by a noninvasive method

Abstract

We recently recorded somatosensory evoked fields (SEFs) elicited by compressing the glabrous skin of the finger and decompressing it by using a photosensor trigger. In that study, the equivalent current dipoles (ECDs) for these evoked fields appeared to be physiologically similar to the ECDs of P30m in median nerve stimulation. We sought to determine the relations of evoked fields elicited by mechanically stimulating the glabrous skin of the great toe and those of electrically produced P40m. We studied SEFs elicited by mechanical and electrical stimulations from the median and tibial nerves. The orientations of dipoles from the mechanical stimulations were from anterior-to-posterior, similar to the orientations of dipoles for P30m. The direction of the dipole around the peak of N20m from median nerve electrical stimulation was opposite to these directions. The orientations of dipoles around the peak of P40m by tibial nerve stimulation were transverse, whereas those by the compression and decompression stimulation of the toe were directed from anterior-to-posterior. The concordance of the orientations in ECDs for evoked fields elicited by mechanical and electrical stimulations suggests that the ECDs of P40m are physiologically similar to those of P30m but not to those of N20m. The discrepancy in orientations in ECDs for evoked field elicited by these stimulations in the lower extremity suggests that electrical and compression stimulations elicit evoked fields responding to fast surface rubbing stimuli and/or stimuli to the muscle and joint.

Ipsilateral primary sensorimotor cortical response to mechanical tactile stimuli

“…Our results objectively confirmed the findings of previous studies [6,7], that cortical cSI responses could be evoked not only by compressive stimuli but also by decompressive stimuli in all subjects. However, in our study, dipole strength of decompressive-cSI responses was smaller than that of compressive stimuli, since compression was approximately 4 times as fast as decompression (39.4±0.6cm/s and 10.1±1.2cm/s, respectively).…”

“…One possible explanation is that the SII responses were related to stimulus strength, in terms of faster stimulus being a stronger stimulus and vice versa, since compression were approximately 4 times as strong (fast) as decompression. However, subjectively strong (fast) decompressive stimuli could not evoke SII responses [6,7]. In addition, despite the difference in nature of the stimuli, weak electrical stimuli (at twice the sensory threshold) could evoke SII responses [21].…”

“…Recently, SEFs elicited by compressive and decompressive stimulation of the index finger glabrous skin [6] and of the great toe [7] have been determined. Although different cSI responses were obtained to compressive and decompressive stimuli, an examiner was needed to stimulate the glabrous skin.…”

Vibration Alert to the Brain: Evoked and Induced MEG Responses to High-Frequency Vibrotactile Stimuli on the Index Finger of Dominant and Non-dominant Hand

“…Previous MEG studies have shown that the somatosensory information processing involves activation in primary and secondary somatosensory cortices (Forss et al, 1994;Hari and Forss, 1999;Karhu and Tesche, 1999;Kakigi et al, 2000;Hoechstetter et al, 2001). Most studies, however, used electrical stimulation of peripheral nerves to activate a broad range of cutaneous receptors or tactile stimulation to activate mainly slowly adapting mechanoreceptors (Forss et al, 1994;Rossini et al, 1996;Jousmäki, 2000;Inoue et al, 2005;Hautasaari et al, 2019). Much less is known about brain responses activated by rapidly adapting mechanoreceptors, i.e., Meissner and Pacinian corpuscles.…”

Somatosensory mechanical response and digit somatotopy within cortical areas of the postcentral gyrus in humans: An MEG study

“…We have recently found that human mechanical touch stimuli induce somatosensory cortical responses not only when glabrous skin is compressed but also when it is decompressed in the index finger [Inoue et al, 2005;Shirai et al, 2004]. It is thought that the somatosensory cortical responses were evoked not only by action potentials from skin receptors such as Pacinian corpuscles but also by offset cortical responses (off-responses) when glabrous skin is decompressed [Crevits et al, 1982;Hari et al, 1987;Noda et al, 1998;Pantev et al, 1996;Wakai et al, 2007].…”