Thomas J. Imig

Physiology of Thalamus and Cortex

Study of the responses of auditory forebrain neurons offers an exciting opportunity to understand the representation of the acoustic environment at the highest levels of the auditory system. During the past decade, echolocating bats have proved to be a valuable model for understanding the processing of biosonar sounds in the cortex. Multiple auditory fields have been identified that contain neurons specialized for extracting a variety of types of biosonar information relating to target velocity, range, size, etc., and in each field the neurons are arranged to form an orderly place map. These elegant studies have been reviewed by Suga (1978, 1982, 1984, 1988).

Elevation sensitivity in the cat’s thalamo‐cortical auditory system: Role of monaural spectral and binaural disparity cues

High‐frequency neurons in auditory cortex (AI) and medial geniculate (MGB) of anesthetized cats are differentially sensitive to monaural and binaural directional cues present in broad‐band noise. Binaural directional (BD) cells depend upon binaural stimuli for azimuth sensitivity, whereas monoaural directional (MD) cells are sensitive to the direction of monaural stimuli. In the MGB, neurons’ spatial receptive fields (SRFs) were obtained using noise bursts presented throughout the frontal hemifield and sound pressure levels that varied over an 80‐dB range. BD cells were broadly tuned to elevation. Those that received excitatory input from one ear and exhibited binaural inhibition or mixed interactions had SRFs that extended throughout one lateral hemifield. Predominantly binaural cells exhibited strong binaural facilitation and had SRFs that formed a vertical band in front of the head. MD cells’ SRFs varied considerably, some were focal areas restricted in azimuth and elevation. Others consisted of multip...