Preliminary studies have shown that in the absence of acoustic stimulation, neurons in n. magnocellularis (NM) and n. laminaris (NL) of the chick discharge synchronously and in a rhythmic pattern. This rhythmic pattern of spontaneous, synchronous discharge occurs only during the embryonic development of hearing. The series of experiments propose to further characterize this pattern of spontaneous discharge. The overall objective is to better understand the role that spontaneous activity plays in the development of auditory system structure and function. Recordings of spontaneous single and multiple unit activity will be made from the auditory brainstem pathway in embryos. The first experiment will determine whether the rate of rhythmic discharge varies as a function of position along the tonotopic gradient in NM and NL. Previous studies have shown that two different rhythms of spontaneous activity are sometimes recorded simultaneously from the same electrode. The second experiment will map the location of these dual rhythms. The question of whether dual rhythms reflect activity from the two sides of the brain will be determined by examining the effect of unilateral cochlear removal on the rhythms. In the third experiment, the question of whether the rhythmic pattern of discharge in NM and NL reflects the activity of the auditory nerve will be evaluated by recording the spontaneous activity in the nerve. In the fourth experiment, the pattern of spontaneous discharge of single units in NM will be quantified by computing interval histograms and autocorrelograms. In the last experiment, the time at which spontaneous activity first occurs and influences postsynaptic function will be evaluated by determining when unilateral cochlear removal first causes an asymmetry in (14C)2-deoxy-D- glucose uptake in the central auditory system.
