Fig. 1.

Representative best frequency map of primary auditory cortex from a naïve adult rat (a and b) and an animal conditioned with nucleus basalis activation separately paired with 2 and 14 kHz tones 300–400 times daily for one month (c and d). Each polygon represents one microelectrode penetration and color represents the best frequency. The objectively defined characteristic frequency of each location is also labeled within each polygon. White hatched regions with bolded black borders indicate regions activated by 2 kHz at 65 dB (a and c) and 14 kHz at 55 dB (b and d) for the naïve and experimental animal. Locations marked with X indicate sites where a reliable frequency could not be objectively defined. In (d), two 14 kHz sites not activated had thresholds at 60 and 57 dB. The line length on the direction marker in (a) shows the scale (0.25 mm).