Intracellular characterization of suppressive responses in supragranular pyramidal neurons of cat primary auditory cortex in vivo.

Several suppressive processes shape the response properties of auditory neurons, namely lateral inhibition, non-monotonic rate level function and excitation/inhibition binaural interaction. By combining intracellular recording from and staining of layers 2 and 3 pyramidal neurons (PNs) in cat primary auditory cortex, we demonstrate the temporal aspects of depolarization and hyperpolarization underlying these suppressions using pure tone stimulation. Two populations can be distinguished by the occurrence of hyperpolarization following onset depolarization (O-DEP). In layer 2 PNs there is an absence of hyperpolarization following O-DEP, while in layer 3 PNs hyperpolarization follows O-DEP. The latency of O-DEP is shortest at the neuron's best frequency. The latency shortens as sound intensity increases. In non-monotonic PNs, hyperpolarization onset becomes shorter as sound intensity increases. This earlier onset of hyperpolarization shortens the duration of the preceding O-DEP, resulting in a decreased O-DEP amplitude. Diverse patterns in the temporal interaction of depolarization and hyperpolarization underlie the binaural suppression interaction. These results demonstrate that diverse suppressive responses result from differences in the temporal timing of excitation and inhibition. The present results also suggest the possibility of distinct connections between PNs responding in a similar manner.