Cerebellar brain inhibition in the target and surround muscles during voluntary tonic activation

Abstract

Motor surround inhibition is the neural mechanism that selectively favors the contraction of target muscles and inhibits nearby muscles to prevent unwanted movements. This inhibition was previously reported at the onset of a movement, but not during a tonic contraction. Cerebellar brain inhibition (CBI) is reduced in active muscles during tonic activation; however, it has not been studied in the surround muscles. CBI was evaluated in the first dorsal interosseus (FDI) as the target muscle, and the abductor digiti minimi (ADM), flexor carpi radialis (FCR), and extensor carpi radialis (ECR) as surround muscles during rest and tonic activation of FDI in fourteen subjects. Cerebellar stimulation was performed under MRI-guided neuronavigation targeting lobule VIII of the cerebellar hemisphere. Stimulus intensities for cerebellar stimulation were based on the resting motor cortex threshold (RMT) and adjusted for the depth difference between the cerebellar and motor cortices. We used 90% to 120% of adjusted RMT as the conditioning stimulus intensity during rest. The intensity that generated the best CBI at rest in the FDI was selected for use during tonic activation. During selective tonic activation of FDI, CBI was significantly reduced only for FDI but not for the surround muscles. Unconditioned MEP sizes were increased in all muscles during FDI tonic activation compared to rest, despite background EMG activity increasing only for the FDI. Our study suggests that the cerebellum may play an important role in selective tonic finger movement by reducing its inhibition in the motor cortex only for the relevant agonist muscle.

Impaired Cerebellum to Primary Motor Cortex Associative Plasticity in Parkinson’s Disease and Spinocerebellar Ataxia Type 3

“…With the established paired-coil protocol ( 8 ), we found that the baseline CBI in the healthy elder subjects was less consistent than the young subjects [84.7 ± 14.9% (Figure 3 ) vs. 78.4 ± 3.1% ( 13 )]. CBI has been supposed to play an important role in selective tonic muscle movement, probably through a topographically specific reduction of inhibition in M1 ( 38 ). The fact that CBI showed a less consistence in the elder subjects might reflex a physiological feature of the aging process in humans.…”

Dysmetria and Errors in Predictions: The Role of Internal Forward Model

“…On the other hand, compound movements were impaired and eliminated [96]. A recent study showed that a PC inhibited and disinhibited an activity of a selective muscle, but not in surrounding muscles, allowing execution of movement performed with a small number of muscles [97]. These findings point to an impairment in coordinating multiple degrees of freedom or synergy.…”

Contribution of transcranial magnetic stimulation to assessment of brain connectivity and networks

“…For instance, tonic muscle contraction reduces the amount of CBI (Pinto et al, 2001) only for the activated muscle, but not for the surrounding ones (Panyakaew et al, 2016). This suggests that the CBI measurement and the CB activation during movement are somatotopic specific.…”