The purpose of the study was to determine the contribution of γ-aminobutyric acidB receptor-mediated intracortical inhibition, as assessed by the cortical silent period (CSP), to the generation of surround inhibition in the motor system. Eight healthy adults (five women and three men, 29.8 ± 9 years) performed isometric contractions with the abductor digiti minimi (ADM)
muscle in separate conditions with and without an index finger flexion movement. The ADM motor evoked potential amplitude and CSP duration elicited by transcranial magnetic stimulation were compared between a control condition in which the ADM was activated independently and during conditions involving three phases (pre-motor, phasic, and tonic) of the index finger flexion movement. The motor evoked potential amplitude of the ADM was greater during the control see more Lumacaftor concentration condition compared with the phasic condition. Thus, the presence of surround inhibition was confirmed in the present study. Most critically, the CSP duration of the ADM decreased during the phasic stage of finger flexion compared with the control condition, which indicated a reduction of this type of intracortical inhibition
during the phasic condition. These findings indicate that γ-aminobutyric acidB receptor-mediated intracortical inhibition, as measured by the duration of the CSP, does not contribute to the generation of surround inhibition in hand muscles. Surround inhibition (lateral inhibition) is a mechanism in sensory system physiology whereby the activation of a neuron is associated with decreased activity of adjacent neurons, a process that sharpens stimulus localization information
(Blakemore et al., 1970). This appears to be a fundamental neural organization pattern because it operates in every sensory system (Nabet & Pinter, 1991). In the motor system, evidence for processes analogous to surround inhibition was originally based on the abnormal movements exhibited by patients with basal ganglia disorders (Denny-Brown, 1967; Hallett & Khoshbin, 1980). Subsequently, these observations were refined into a model that proposed that the motor command consists of an excitatory component that executes a desired movement and an inhibitory component that suppresses an unwanted IKBKE movement (Mink, 1996). Recent studies have attempted to determine the presence, functional significance, and physiological mechanisms underlying surround inhibition in the motor system using transcranial magnetic stimulation (TMS) (Beck & Hallett, 2011). In these studies, surround inhibition was quantified as the reduction in the motor evoked potential (MEP) obtained from a muscle not involved in a given task. Furthermore, it was shown that surround inhibition was confined to the initiation phase of movement (Beck et al., 2008), modulated by task (Beck et al., 2009b; Shin et al.