Auditory spatial tuning of cortical neurons is sharpened in cats with early blindness

1. The specificity for the location of a sound source in azimuth was measured in single neurons of the anterior ectosylvian (AE) region of the cat's cortex, which includes the anterior auditory field (AAF) and the anterior ectosylvian auditory field (AEA). 2. The influence of visual experience on auditory spatial tuning of these neurons was determined by comparing responses in cats with binocular deprivation from birth with those in normal control cats. 3. Spatial tuning was measured under near free-field conditions by presenting broadband sounds through a speaker in seven different azimuthal locations, from -60 to +60 degree at 20 degree intervals. Elevation was constant at the cats' ears. 4. In normal cats, a little over one-half of the neurons in the AE region (82/146 = 56%) showed some degree of azimuthal spatial tuning, as defined by at least a 2:1 ratio of responses between best and worst location. The rest (44%) were omnidirectional. 5. In binocularly deprived cats, a significantly higher proportion (70/82 = 86%) of the neurons in the AE region were spatially tuned. Only 14% were omnidirectional. Median spatial tuning width was significantly sharper than in normal cats. 6. We conclude that visual deprivation from birth induces intermodal changes that enhance the response specificity of neurons in the auditory cortex. These modifications may constitute the neural basis of behavioral compensation for early blindness.