Functional organization of the auditory thalamus in the guinea pig

Abstract

The auditory thalamus of the guinea pig was investigated with microelectrode mapping techniques. Pure tones of varying frequencies and amplitudes were used as acoustic stimuli, and frequency tuning curves were recorded from 840 multi-units or single cells. The neurons in ventral nucleus of the medial geniculate body (MGv) respond vigorously to pure tones; they have mostly narrow frequency tuning curves and short response latencies (8-12 ms). The MGv is tonotopically organized: High frequencies (16-21 kHz) are located rostrally; the intermediate frequencies (2.8-11 kHz) lie caudomedial of the high frequencies, while the low frequencies (0.5-2.8 kHz) run as a continuous band from rostrolateral to caudomedial. These data confirm a model of tonotopy of the guinea pig MGv which was based on anatomical data from previous tract-tracing experiments. In these experiments, thalamocortical connections were investigated with retrogradely transported tracers (horseradish peroxidase, fluorescent dyes, Redies et al. 1989b). Dorsal, lateral and in part also ventral to MGv, the neuronal responses to pure tones were often less vigorous than in MGv. Many neurons had broad frequency tuning curves, and in nearly all recordings from this region, the response latencies were longer than 12 ms. A tonotopic organization was not apparent here. From the response properties and the location relative to MGv, we concluded that this area corresponds to the shell nucleus of the MG.

Corticofugal Modulation on Both on andoff Responses in the Nonlemniscal Auditory Thalamus of the Guinea Pig

“…We confirmed in the present study that the organization of the characteristic frequencies is well matched with that of previous investigators: high frequencies were located rostrally, intermediate frequencies in the center rostrocaudally, and low frequencies caudally (Redies and Brandner 1991). It was confirmed in the present study that many OFF or ON-OFF neurons were located on the border between the lemniscal and nonlemniscal nuclei or in the nonlemniscal nuclei of the MGB (He 2001).…”

“…The MGcm, which is equivalent to the magnocellular division of the MGB in the cat and monkey, consists of large and deeply Nissl-stained cells and projects to the entire auditory cortex (Redies and Brandner 1991), hinting at a power to adjust the total activity of the auditory cortex. The MGcm is involved in the integration of multi-sensory afferents (Edeline 1990;Edeline and Weinberger 1992;Wepsic 1966;Winer and Morest 1983).…”

Identification of subdivisions in the medial geniculate body of the guinea pig

“…Neurones in the ventral MGB tend to be sharply tuned to tonal stimuli and have an orderly alignment of characteristic frequencies (Edeline et al, 1999;He, 2001He, , 2002Redies and Brandner, 1991;Rodrigues-Dagaeff et al, 1989). Conversely, neurones in the dorsal MGB tend to have broad tuning curves and no tonotopic characteristic frequency arrangement (Calford, 1983;Calford et al, 1983;Edeline et al, 1999).…”

Thalamocortical and Corticothalamic Interaction in the Auditory System

“…In the cat, the fibrodendritic orientation confers a laminar structure upon the MGv and the isofrequency contours parallel to this laminae arrangement with the low-frequency region located laterally, the middle-frequency region caudomedially, and the high-frequency region rostromedially [20][21][22][23] . In the guinea pig, the tonotopic map runs rostrocaudally with high frequencies located rostrally and low frequencies caudally [24,25] . Neurons in the MGv have extremely uniform properties, which include high levels of spontaneous activity, sharp frequency tuning, and the shortest latency (8-15 ms) responses to acoustic stimuli.…”