Associative plasticity in the human motor cortex is enhanced by concurrently targeting separate muscle representations with excitatory and inhibitory protocols

Abstract

Paired associative stimulation (PAS) induces changes in the excitability of human sensorimotor cortex that outlast the procedure. PAS typically involves repeatedly pairing stimulation of a peripheral nerve that innervates an intrinsic hand muscle with transcranial magnetic stimulation over the representation of that muscle in the primary motor cortex. Depending on the timing of the stimuli (interstimulus interval of 25 or 10 ms), PAS leads to either an increase (PAS25) or a decrease (PAS10) in excitability. Both protocols, however, have been associated with an increase in excitability of nearby muscle representations not specifically targeted by PAS. Based on these spillover effects, we hypothesized that an additive, excitability-enhancing effect of PAS25 applied to one muscle representation may be produced by simultaneously applying PAS25 or PAS10 to a nearby representation. In different experiments prototypical PAS25 targeting the left thumb representation [abductor pollicis brevis (APB)] was combined with either PAS25 or PAS10 applied to the left little finger representation [abductor digiti minimi (ADM)] or, in a control experiment, with PAS10 also targeting the APB. In an additional control experiment PAS10 targeted both representations. The plasticity effects were quantified by measuring the amplitude of motor evoked potentials (MEPs) recorded before and after PAS. As expected, prototypical PAS25 was associated with an increase in MEP amplitude in the APB muscle. This effect was enhanced when PAS also targeted the ADM representation but only when a different interstimulus timing (PAS10) was used. These results suggest that PAS-induced plasticity is modified by concurrently targeting separate motor cortical representations with excitatory and inhibitory protocols.

Does sonification of action simulation training impact corticospinal excitability and audiomotor plasticity?

“…While plasticity arising from motor learning is long-lasting (Dayan and Cohen 2011), the spacing between our two protocols may have affected the level of attention during aPAS. This view is supported by evidence that participants' level and focus of attention affect the outcome of PAS (Kamke et al 2012(Kamke et al , 2016Stefan et al 2004). That is, it is possible that participants may have been unable to sustain high level of attention to the protocol, or worst may have been in a state of drowsiness.…”

Stimulus uncertainty enhances long-term potentiation-like plasticity in human motor cortex

“…This stimulus was followed 25 ms later by a TMS pulse to the cortical representation targeted by the peripheral stimulation in the right motor cortex. The left hand/right motor cortex was chosen because it allowed us to directly compare the results of the present study with previous PAS experiments conducted in our laboratory (Kamke, Hall, et al, 2012;Kamke, Nydam, Sale, & Mattingley, 2016;Kamke et al, 2014), and because it has been shown previously that there are no hemispheric differences in PAS-effectiveness (Ridding & Flavel, 2006). The TMS intensity was adjusted to evoke an MEP of ~0.5-1mV in peak-to-peak amplitude (test intensity).…”