Responses to tones of single cells in nucleus magnocellularis and nucleus angularis of the redwing blackbird (Agelaius phoeniceus)

Responses to tones were recorded from single cells in the brainstem auditory nuclei n. magnocellularis and n. angularis of the redwing blackbird (Agelaius phoeniceus). Whereas 30% of the cells in angularis had rates of spontaneous activity less than 40/s, only 5% of those in magnocellularis had rates this low. Two types of response maps are found in n. angularis. Type III maps have a single excitatory area with regions of inhibition on one or both sides. Type IV maps have a region of excitation at sound levels near threshold at the best frequency of the cell; at higher levels the best frequency is inhibitory; there can be broad bands of inhibition or interleaved bands of inhibition and excitation at higher levels. Cells in magnocellularis show only Type III response maps with generally weaker inhibitory sidebands than those in angularis. Responses to excitatory tone bursts in magnocellularis are "primary-like" in that they show a rapid increase in discharge rate at tone onset followed by a decrease in rate of 30 to 70% over the next 50 ms. On the other hand, a number of response types are seen in angularis, including "primary-like", "pauser", and "onset". These results for magnocellularis and angularis are compared with results from their presumed mammalian homologues, the anteroventral cochlear nucleus, and posteroventral and dorsal cochlear nuclei, respectively. Finally, the relationship between response patterns in these avian brainstem nuclei and those seen in higher auditory centers is considered.