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PubMed1991

Spectrotemporal receptive fields of neurons in cochlear nucleus of guinea pig.

Spectrotemporal receptive fields (STRFs) [Hermes et al., Hear. Res. 5, 147-178, 1981] for neurons in the cochlear nuclei (CN) of guinea pig were estimated. Sixteen periodic segments of bandlimited, synthesized noise evoked replicable, distinctive period histograms for spike discharges. All driven units in the major divisions of the CN having their characteristic frequency (CF) within the noise bandlimits had unique STRFs for a given intensity of noise stimulation. The STRF maximum corresponded to the unit's CF, and details of the STRF patterns differed over CN divisions and response classes derived from tonebursts. The sizes of features in STRFs from this mammal appeared significantly smaller in their temporal and spectral extents than those reported in the torus semicircularis of an amphibian and were roughly comparable to the few units reported from cat ventral CN [Eggermont et al., Quart. Rev. Biophys. 16, 341-414, 1983]. STRFs, as they are presently obtained, provide useful insight into some aspects of afferent processing and perhaps connectivity, but their interpretation is specific to the level of stimulation and limited by the need to choose a specific energy distribution to represent the stimulus.

Acoustic Stimulation↗
PubMedDate not supplied

Response characteristics of cochlear nucleus neurons to vowel sounds.

Most studies in auditory neurophysiology have utilized tonal stimuli to determine the coding properties of neurons in the cochlear nuclei. In this investigation of the kangaroo rat, cochlear nuclei, neuronal responses to vowel sounds, as well as tones, were studied. The vowel sounds, each about 40 msec in duration were: see article. Five were linked together to form a 200 msec stimulus and various combinations of five vowel sounds provided us with 18 different stimuli. The results show that neurons in the cochlear nuclei are remarkably sensitive and selective to vowel sounds. Furthermore, the responses of these neurons to pure tones do not provide a complete basis to predict the types of responses to the vowel sounds. More significant is the finding that the neural discharge rate and pattern of discharge to a particular vowel may depend on where the vowel appears in the stimulus and what other vowel precedes it. This vowel positional effect is not the same for every neuron. We have called this phenomenon a neural "set".

Acoustic Stimulation↗
PubMed1977

Descending inputs to the octopus cell area of the cat cochlear nucleus: an electron microscopic study.

Large, unilateral lesions of the superior olivary complex (SOC) were made in 18 adult cats. Terminal degeneration was studied electron micrsocopically in the octopus cell area (OCA) of the caudal cochlear nuclei both ipsilateral and contralateral to lesions, after 1 to 14 postoperative days. Three synaptic types (OCA types 1, 2, and 3) have been previously described upon octopus cell somas and dendrites and types 1 and 2 identified as cochlear in origin. The present study shows a new synaptic ending (OCA type 4) on small octopus cell dendrites as well as dendrodendritic contacts. Following SOC ablations, type 4 endings degenerated in the OCA ipsilateral to the lesion. In the COA contralateral to the same lesion, however, degeneration was found in type 3 terminals ending upon more proximal octopus cell dendrities and upon somas. Ipsilateral terminal degeneration occurred between two and four postoperative days, was rare by seven days, and was gone by 14 days after these lesions. However, contralateral terminal degeneration was rare until four days, was most abundant after seven days, and was still present after 14 postoperative days. The different synaptic types and time courses of degeneration in the ipsilateral versus the contralateral OCA, suggested that type 4 endings originate from an ipsilateral source, such as the lesioned periolivary region, while type 3 endings originate from the contralateral SOC or from higher contralateral nuclei. Other evidence for these sources and possible functions of these descending inputs are briefly discussed.

Animals↗