Abstract
In many mammals, mirror-symmetric tonotopic organization of core fields in auditory cortex has been reported in electrophysiological and imaging studies. Studies in guinea pig auditory cortex have concluded that primary auditory field (AI) and dorsocaudal field (DC), the two core fields for guinea pigs, have mirror-symmetric tonotopy. This conclusion, however, is based in responses in the two fields to tones of a limited range of frequency. By using high-resolution imaging techniques with voltage-sensitive dye RH-795, we recorded responses in AI, DC, and several belt regions of anesthetized guinea pigs to tones of a broader range of frequencies, and examined the tonotopic organization of DC. In agreement with previous studies, DC had a tonotopy with a frequency axis in a caudal-to-rostral direction. Lower frequency tones activated a caudal part of DC and a rostral part of AI; these activated areas gradually approached each other with the increase of stimulus tone frequency. However, characteristic shapes of activation were observed in DC, according to tone frequencies. High frequency tones (12-24 kHz) activated a strip area, as reported in previous studies. Low frequency tones (0.25-1 kHz), however, activated a spot-like area. The area activated by middle frequency tones (2-8 kHz) was C-shaped, embracing the spot-like area activated by lower frequency tones. [J Physiol Sci. 2007;57 Suppl:S104]
