Despite selleck compound the determination of the impairment of some of these pathways in FHD, none of these studies were able to establish the specific cortical pathway underlying the generation of surround inhibition in healthy subjects. For example, intracortical and intercortical circuits including short intracortical inhibition (Sohn & Hallett, 2004a; Beck et al., 2008), long intracortical inhibition (LICI) (Sohn & Hallett, 2004b), intracortical facilitation (Sohn & Hallett, 2004b), interhemispheric inhibition (Beck et al., 2009c), dorsal pre-motor inhibition (Beck et al., 2009a), and ventral pre-motor inhibition (Houdayer et al., 2012) were not responsible for surround inhibition. Similarly, short afferent

inhibition (Richardson et al., 2008), long-latency afferent inhibition (Pirio Richardson et al., 2009), and cerebellar inhibition (Kassavetis et al., 2011) were also not involved. Collectively, these results are surprising given the functional

importance and number of the cortical pathways examined in these studies. The CSP is another index of intracortical inhibition that has been used extensively to study GABAB-mediated inhibition processes during voluntary contractions. In the present study, it was hypothesised that the mechanisms underlying the CSP could participate in the generation of surround inhibition. This expectation was based on several inter-related lines of evidence. First, GABAergic neurons are the most numerous and important class of inhibitory interneurons in the motor cortex (Jones, 1993; Keller, 1993). Selleck DAPT Second, the CSP duration of agonist muscles has been shown to be abnormal in FHD (Ikoma et al., 1996; Chen et al., 1997; Filipovic et al., 1997) and Parkinson’s disease (Priori et al., 1994a; Nakashima et al., 1995), which are the same patient populations

that have exhibited impaired surround inhibition (Sohn & Hallett, 2004a; Shin et al., 2007; Beck & Hallett, 2011). Third, the differential modulation of CSP duration in different tasks suggests that this type of intracortical inhibition has functional O-methylated flavonoid significance in the execution of fine motor tasks involving hand muscles (Tinazzi et al., 2003; Sale & Semmler, 2005). Fourth, no previous studies had examined the possible role of the CSP in the generation of surround inhibition. In fact, the standard paradigm in these studies did not permit CSP duration quantification because the surround muscle was required to remain at rest during agonist muscle activation. Therefore, a modification of a previously developed experimental methodology (Sohn et al., 2005) was utilised to assess CSP duration in an active surround muscle during remote muscle activation. The MEP amplitude of the surround ADM muscle was greater during independent activation compared with the phasic movement phase of the accompanying index finger flexion.