Frontiers in Systems Neuroscience Systems Neuroscience

Abstract

studies by Murthy and Fetz (1992) showed that oscillations are also present in primary somatosensory cortex (S1), and that there is beta-band coherence between M1 and S1. Electrocorticogram (ECOG) recordings in humans with intractable epilepsy reveal coherence between M1 and S1 (Ohara et al., 2001). In fact, S1 oscillations in monkeys actually have a larger amplitude than those in M1 (Witham and Baker, 2007). Using Granger causality analysis, Brovelli et al. (2004) and Tsujimoto et al. (2009) demonstrated causal influences from S1 to M1 and also from S1 to area 5 of PPC in the beta band in monkeys. Coherence between cortical activity and contralateral muscles may be mediated by both motor and somatosensory pathways. Riddle and Baker (2005) used cooling of the forearm to increase peripheral conduction times in human subjects; the changes in corticomuscular coherence phase suggested that afferent feedback pathways, as well as descending motor output, contributed to cor-ticomuscular coherence. Baker and Baker (2003) investigated the effects on corticomuscular coherence of benzodiazepine administration in humans, and concluded that the results were incompatible with simple transmission of oscillations from cortex to muscle by descending pathways. Finally, muscle spindle afferents in monkeys show coherence with EMG (Baker et al., 2006), providing direct evidence for ascending transmission of oscillatory information. The evidence above suggests that the somatosensory system is important in generating corticomuscular coherence, but this remains controversial. Ohara et al. (2000) found coherence between