Temporal dynamics of the tonotopic map in awake primates

Wednesday, October 26, 2011 — Poster Session IV
2:00 p.m. – 4:00 p.m.	Natcher Conference Center	NIMH	NEURO/BEHAV/SENSYS-12

* FARE Award Winner

Authors

• M Fukushima
• R Saunders
• D Leopold
• M Mishkin
• B Averbeck

Abstract

One of the fundamental features of sensory cortex is that it topologically maps the physical attributes of sensory stimuli. In the macaque auditory cortex, the attribute mapped is sound frequency, yielding tonotopic maps on the supratemporal plane (STP). While neural responses in these areas have been studied in detail, the spatiotemporal activation of these maps to the onset of acoustic stimuli is not well understood in awake monkeys. To examine this issue, we chronically implanted four micro-electrocorticographic arrays in each of two monkeys, allowing for 128 parallel measurements of field potentials from the surface on the STP as well as the caudal superior temporal gyrus. First we examined the auditory frequency tuning of auditory evoked potentials at conventional field potential frequency ranges. This analysis revealed tonotopic maps that reversed frequency direction at putative areal boundaries, with the smoothest tonotopic-reversal map by the high-gamma band power. Next, we estimated when each site showed significant discrimination among different stimulus frequencies by evaluating the high-gamma power. We found that the onset time of the discrimination increased along the caudal-to-rostral as well as the medial-to-lateral axes, consistent with the hypothesis that auditory information is serially processed in those two directions in parallel.

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