Dynamics of Spectro - Temporal Tuning in Primary Auditory Cortex of the Ferret

In this paper, we explore spectro-temporal tuning in primary auditory cortex following a sudden change in spectro-temporal content. We previously characterized the steady-state spectrotemporal tuning properties of cortical cells with respect to broadband sounds by presenting sounds with a spectro-temporal envelope of constant spectral density and angular frequency for several seconds. However, since speech and other natural sounds have spectro-temporal features that change substantially over milliseconds, we studied the dynamics of tuning by using stimuli of constant level but alternating between a flat spectro-temporal envelope and a modulated envelope with well defined spectral density and angular frequency. This allowed us to define the tuning of cortical cells to speech-like and other rapid transitions, at the order of milliseconds, as well as the time evolution of this tuning in response to the features of a new sound. We find that cortical neurons can be characterized by a lag-dependent modulation transfer function. This characterization, when measured through to steady-state, is equivalent to the classical spectrotemporal receptive field.