Contextual modulation of frequency tuning of neurons in the rat auditory cortex.

In a natural acoustic environment, sound stimuli often occur in a contextual acoustic stream. The aim of the present study was to determine how the frequency tuning of auditory cortical neurons is affected by an acoustic context. A forward masking paradigm was used to determine the frequency receptive fields of rat auditory cortex neurons under quiet and sequential sound conditions. The frequency receptive fields of a cortical neuron were modulated dynamically by a preceding sound stimulus. At a fixed interstimulus interval (ISI), if the preceding sound level was constant, the receptive fields of most neurons were modulated to the greatest extent when the preceding sound frequency was at or near the characteristic frequency of the neuron; if the preceding sound frequency was constant, the modulation was increased with increasing sound stimulus level. When both the frequency and the level of the preceding sound were fixed, the modulation decreased with increasing interstimulus interval. The results indicate that the frequency tuning of auditory cortical neurons is plastic and dynamically modulated in a reverberant acoustical environment, and the degree of modulation depends on both the frequency tuning of the neuron and the contextual acoustical stream.