Plasticity in the rat posterior auditory field following nucleus basalis stimulation.

Classical conditioning paradigms have been shown to cause frequency-specific plasticity in both primary and secondary cortical areas. Previous research demonstrated that repeated pairing of nucleus basalis (NB) stimulation with a tone results in plasticity in primary auditory cortex (A1), mimicking the changes observed after classical conditioning. However, few studies have documented the effects of similar paradigms in secondary cortical areas. The purpose of this study was to quantify plasticity in the posterior auditory field (PAF) of the rat after NB stimulation paired with a high-frequency tone. NB-tone pairing increased the frequency selectivity of PAF sites activated by the paired tone. This frequency-specific receptive field size narrowing led to a reorganization of PAF such that responses to low- and mid-frequency tones were reduced by 40%. Plasticity in A1 was consistent with previous studies -- pairing a high-frequency tone with NB stimulation expanded the high-frequency region of the frequency map. Receptive field sizes did not change, but characteristic frequencies in A1 were shifted after NB-tone pairing. These results demonstrate that experience-dependent plasticity can take different forms in both A1 and secondary auditory cortex.