Behavioural and neurophysiological markers reveal differential sensitivity to homeostatic interactions between centrally and peripherally applied passive stimulation

Abstract

Repetitive transcranial magnetic stimulation (rTMS) is an effective tool for inducing functional plastic changes in the brain. rTMS can also potentiate the effects of other interventions such as tactile coactivation, a form of repetitive stimulation, when both are applied simultaneously. In this study, we investigated the interaction of these techniques in affecting tactile acuity and cortical excitability, measured with somatosensory evoked potentials after paired median nerve stimulation. We first applied a session of 5-Hz rTMS, followed by a session of tactile repetitive stimulation, consisting of intermittent high-frequency tactile stimulation (iHFS) to a group of 15 healthy volunteers ("rTMS + iHFS" group). In a second group ("rTMS w/o iHFS"), rTMS was applied without iHFS, with a third assessment performed after a similar wait period. In the rTMS w/o iHFS group, the 5-Hz rTMS induced an increase in cortical excitability that continued to build for at least 25 min after stimulation, with the effect on excitability after the wait period being inversely correlated to the baseline state. In the rTMS + iHFS group, the second intervention prevented the continued increase in excitability after rTMS. In contrast to the effect on cortical excitability, rTMS produced an improvement in tactile acuity that remained stable until the last assessment, independent of the presence or absence of iHFS. Our results show that these methods can interact homeostatically when used consecutively, and suggest that different measures of cortical plasticity are differentially susceptible to homeostatic interactions.

Effects of age and expertise on tactile learning in humans

“…Our results show that this previous experience of plastic changes causes experts to have stronger intervention‐related improvement than non‐experts. This is in line with the concept of meta‐plasticity (Gatica Tossi et al ., ).…”

“…It seems that tactile expertise as a result of the frequent stimulation of the fingertips makes learning more effective and raises the upper performance limit, as experts were found to learn more than non‐experts. This can be referred to as meta‐plasticity, as a higher‐order form of plasticity, where previous experiences that had led to plastic changes influence subsequent plasticity in response to new experiences (Gatica Tossi et al ., ). Thus, meta‐plasticity increases the general preparedness to learn (Morrison, ; Hulme et al ., ).…”

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

“…Mechanical tactile stimulation (MS) is a somatosensory input tool and was reported to alter neurophysiological and sensory skills [ 17 – 25 ]. A MS of 1 Hz for 3 h lowered the two-point discrimination threshold and shifted the localization of the N20 dipole of the index finger [ 19 , 20 ].…”

Metaplasticity in human primary somatosensory cortex: effects on physiology and tactile perception

“…Of specific interest was the comparison of a single protocol of cTBS to iTBS to investigate their similarities and differences and dual protocols of cTBS and iTBS to investigate their metaplasticity effects. Our data indicate that cTBS and iTBS have similar effects such that measures of intracortical inhibition and touch perception are altered without changes to the first SEP, bearing strong similarity to the effects that follow intermittent high-frequency tactile stimulation, 5 Hz repetitive TMS (rTMS), or their consecutive combination (Gatica Tossi et al 2013b). Additionally, consecutive identical TBS protocols evoke metaplasticity in measures of tactile perception only, suggesting that metaplasticity operates via changes in intracortical inhibition rather than changes in excitatory mechanisms within SI.…”