New Field With Tonotopic Organization in Guinea Pig Auditory Cortex

1 Department of Sensory and Cognitive Physiology, Graduate School of Medical and Pharmaceutical Sciences, Kumamoto University, Kumamoto; and 2 Division of Electrical, Electronic, and Information Engineering, Graduate School of Engineering, Osaka University, Suita, Japan Submitted 4 July 2006; accepted in final form 13 October 2006 In guinea pig auditory cortex, two core areas, a primary area (AI) and a dorsocaudal field (DC), and two belt regions ventral to AI and DC (VRB and VCB) with an intermediate zone (T) in between, together with a small field (S) rostral to AI, have been reported in single-electrode studies although field S and zone T have not been observed in imaging studies. Using a high-resolution in vivo optical-imaging system with the voltage-sensitive dye RH-795, we report here the successful imaging of a rostral small field and zone T and a ventral-to-dorsal frequency gradient in zone T. Further, we found that VRB can be subdivided into two areas, a ventrorostral field (VR) with properties similar to those reported for VRB, and a ventrocaudal field (VC) with novel properties. With increasing stimulus tone frequency, activation in VR shifted caudally while activation in VC shifted rostrally. Thus we have newly identified field VC that has mirror-symmetric tonotopy to that of VR. Address for reprint requests and other correspondence: W.-J. Song, Dept. of Sensory and Cognitive Physiology, Graduate School of Medical and Pharmaceutical Sciences, Kumamoto University, Kumamoto 860-8556, Japan (E-mail: song{at}kaiju.medic.kumamoto-u.ac.jp )