Tonotopic organization in the central auditory pathway of the mongolian gerbil: A 2‐deoxyglucose study

Abstract

The uptake of 2-deoxyglucose (2-DG) was employed to map functional activation of the central auditory pathway in the mongolian gerbil, during 85 dB SPL stimulation with pure tonal stimuli at frequencies of 0.75, 3.0, or 12.0 kHz. Pure tones produced foci of very high 2-DG uptake, when compared to adjacent tissue, in the cochlear nucleus, superior olivary complex, and inferior colliculus. Less distinct areas of elevated 2-DG uptake were seen in the dorsal and ventral nuclei of the lateral lemniscus, medial geniculate nucleus, and auditory cortex. Little or no change in the distribution of 2-DG uptake was noted in the nucleus of the trapezoid body. The location of discrete regions of relatively high 2-DG uptake varied systematically with stimulus frequency. The tonotopic organization demonstrated by 2-DG mapping agreed well with the results of previous electrophysiological studies for most structures. However, in the inferior colliculus, stimulus-evoked increases in 2-DG uptake were found to occur in a fixed pattern of three to four bands across the central nucleus, which did not correspond to any previously reported anatomical or physiological organization. Pure tonal stimuli activated discrete portions of this banding pattern. Also, a small area at the ventromedial edge of the colliculus was more broadly tuned than other regions of the nucleus. It is concluded that 2-DG uptake is well suited to the investigation of tonotopic organization. This technique reveals patterns of activation which have not been observed with other methodologies.

Single-unit labeling of medial olivocochlear neurons: the cochlear frequency map for efferent axons

“…The CF-to-position mapping of MOC neurons described in the present study is one of many such tonotopic mappings in the auditory pathway (Clopton et al 1974;Ryan et al 1982;Friauf 1992;Muniak et al 2013). Present results suggest that the MOC mapping is similar to the auditorynerve fiber mapping, either indistinguishable from it (for MOC Ipsi units) or just apical to it (for MOC Contra units, although these data are more limited).…”

Unilateral cochlear ablation before hearing onset disrupts the maintenance of dorsal nucleus of the lateral lemniscus projection patterns in the rat inferior colliculus

“…Although much more is known about the developmental mechanisms of glutamatergic circuit formation, important progress has been made in understanding the development of inhibitory circuits in the auditory brainstem such as those in the SOC (Kandler, 2004;Kandler and Gillespie, 2005). In the mature SOC, inhibitory projections from the medial nucleus of the trapezoid body (MNTB) are distributed systematically along narrow strips in LSO corresponding to precise tonotopic organization (Ryan et al, 1982;Friauf, 1992). Before hearing onset in the gerbil and the rat, the initial distribution of MNTB axonal arbors and synapses in the LSO is much broader than that present in the mature animal.…”

Responses of neurons in the inferior colliculus to a dynamic-level stimulus that simulates a sound source with varying distance

“…The data set included only the ''sustained'' type of units, since the ''onset'' type of units did not produce a reliable number of spikes for the long-duration stimuli used in the present study. It is likely that many of the units were recorded from the central nucleus of the IC because the neurons had distinct frequency tuning curves and the distribution of the units' best frequencies in the IC was roughly as predicted from the tonotopic map of the IC that was reported by the previous studies (e.g., [4]). The units' best frequencies ranged between 1,511 and 15,000 Hz (median 5,424 Hz).…”