In the macaque auditory cortex, these direct measurements have revealed detailed aspects of the sound encoding properties within various frequency bands of the field potentials

(Lakatos et al., 2005a, Chandrasekaran and Ghazanfar, 2009, Steinschneider et al., 2008, Kayser et al., 2009 and Fishman and Steinschneider, 2010). This approach, however, is not well suited to examining spatiotemporal activation profiles from a large expanse of the cortex. Optical imaging of voltage-sensitive dyes has revealed spatiotemporal activation patterns in sensory cortex (Huang et al., 2004, Xu et al., 2007 and Wu et al., 2008), but HDAC inhibitor mechanism this method cannot measure neural activity from intrasulcal cortical areas such as the STP. On the other hand, fMRI can probe the entire brain simultaneously, but it has low temporal resolution. In the present study, we circumvented these limitations by adopting intracranial microelectrocorticography (μECoG). The μECoG arrays used in the current study had finer spacing between sites (1 mm) Selleck SP600125 than that of standard ECoG grids. This approach allowed us to extract the fine tonotopic representation in the macaque auditory cortex on the STP in the lateral sulcus at high temporal resolution.

Mirror symmetric tonotopic maps that reverse at areal boundaries in auditory cortex are one of the main features shared by many primate species, including humans (Formisano et al., 2003, Da Costa et al., 2011 and Hackett, out 2011). In awake macaques, tonotopic maps have been identified using single-unit recordings (Recanzone et al., 2000, Kusmierek and Rauschecker, 2009 and Scott et al., 2011), but maps have not been identified in far rostral sites on

the STP, and, in fact, there are only a few studies that have recorded single units from rostral areas (Kikuchi et al., 2010 and Perrodin et al., 2011). In the current study, we identified mirror symmetric tonotopic maps from primary to rostral areas, using the high-gamma power of the evoked field potential. Previous studies have shown that in the macaque primary auditory cortex tuning curves for stimulus frequency obtained from multi-unit spiking activity were better correlated with high-gamma power in local field potentials (LFPs) than with power in the lower frequency components of the LFP (Kayser et al., 2007). Previous studies in other cortical sensory areas have similarly demonstrated that spiking activity has a closer relation to high-gamma power than to power in lower frequencies (Liu and Newsome, 2006 and Ray et al., 2008). These studies suggest that the tonotopic maps obtained from high-gamma band power in our data reflect spiking activity in the vicinity of each contact, presumably from upper layers of cortex since the μECoG arrays were placed on the cortical surface.