Use-Dependent Hemispheric Balance

Abstract

In the human brain, homologous regions of the primary motor cortices (M1s) are connected through transcallosal fibers. Interhemispheric communication between the two M1s plays a major role in the control of unimanual hand movements, and the strength of this connection seems to be dependent on arm activity. For instance, a lesion in the M1 can induce an increase in the excitability of the intact M1 and an abnormal high inhibitory influence onto the damaged M1. This can be attributable to either the disuse of the affected limb or the overuse of the unaffected one. Here, to directly investigate cortical modifications induced by an abnormal asymmetric use of the two limbs, we studied both the excitability of the two M1s and transcallosal interaction between them in healthy subjects whose right hand was immobilized for 10 h. The left "not-immobilized" arm was completely free to move in one group of participants (G1) and limited in the other one (G2). We found that the non-use reduced the excitability of the left M1 and decreased the inhibitory influence onto the right hemisphere in the two groups. However, an increase in the excitability of right M1 and a deeper inhibitory interaction onto the left hemisphere were evident only in G1. Thus, modifications in the right M1 were not directly produced by the non-use but would depend on the overuse of the "not-immobilized" arm. Our findings suggest that the balance between the two M1s is strongly use dependent.

Short-term immobilization influences use-dependent cortical plasticity and fine motor performance

“…Previous work has reported reduced MEPs following short-term immobilisation (i.e., < 4 days; Facchini et al, 2002, Huber et al, 2006, Avanzino et al, 2011, Ngomo et al, 2012, Avanzino et al, 2014, Rosenkranz et al, 2014, but increased MEPs following long-term immobilisation (i.e., > 10 days; Zanette et al, 1997, Zanette et al, 2004, Roberts et al, 2007, Clark et al, 2008. Within the current study, immobilisation caused a reduction in MEP amplitude without a change in RMT.…”

Selective impairment of sensorimotor representations following short-term upper-limb immobilization

“…In the latter case, short-term limb immobilisation (10-12 hours to 4 days) appears as a novel paradigm to explore the continuous and rapid updates to the sensorimotor representations caused by peripheral factors. Neuronal evidence has indicated that limb non-use induces a decrease in motor cortex excitability contralateral to the immobilised limb (Avanzino, Bassolino, Pozzo, & Bove, 2011;Avanzino, Pelosin, Abbruzzese, Bassolino, Pozzo, & Bove, 2013;Facchini, Romani, Tinazzi, & Aglioti, 2002;Huber, Ghilardi, Massimini, Ferrarelli, Riedner, Peterson, & Tononi, 2006). In parallel, behavioral studies have shown that sensorimotor restriction alters the central functioning of the sensorimotor system and may disrupt motor performance (Bassolino, Bove, Jacono, Fadiga, & Pozzo, 2012;Huber et al, 2006;Moisello, Bove, Huber, Abbruzzese, Battaglia, Tononi, & Ghilardi, 2008) or action simulation (Meugnot, Almecija, & Toussaint, 2014;Meugnot, Agbangla, Almecija, & Toussaint, 2015;Toussaint & Meugnot, 2013) of the restricted and unrestricted limbs.…”

Applications of TMS to Study Brain Connectivity

“…In contrast to motor training, limb immobilization has the opposite effect increasing IHI targeting the immobilized cortex (Avanzino et al 2011(Avanzino et al , 2013. Interestingly, if arm immobilization is coupled with proprioceptive sensory input to the immobilized hand IHI balances remained unchanged (Avanzino et al 2013), suggesting that in part interhemispheric interaction modulations may also be attributable to a reduction of proprioceptive information.…”