Commissural connections between the auditory cortices of the rat

doi:10.1016/0006-8993(90)90310-8

Brain Research

Volume 509, Issue 1, 12 February 1990, Pages 71-79

https://doi.org/10.1016/0006-8993(90)90310-8 Get rights and content

Abstract

The pattern of commissural connections of the rat auditory cortex (AC) was investigated with injections of wheat germ agglutinated horseradish peroxidase into the AC. Homotopic and heterotopic patches of neurons were retrogradely labeled in the contralateral hemisphere. Each injection labeled neurons at the corresponding contralateral site, i.e. the homotopic site. In addition, retrogradely labeled neurons were found at non-corresponding locations in contralateral AC, i.e. at heterotopic locations. The pattern of heterotopic labeling changed systematically with the injections. Mapping rules were established that led to the parcellation of areas 41 and 36 into 6 fields. Four fields were defined in Krieg's area 41 (primary AC) and two fields in Krieg's area 36 (secondary AC). In area 41 the heterotopic connection is not reciprocal; in area 36, however, heterotopic projections are organized reciprocally. Contrary to the visual cortex, homotopic and heterotopic projection neurons were equally distributed across the cortical laminae. With double-label experiments it could be shown that a considerable number of the neurons in area 41 bifurcate and project to homotopic as well as to heterotopic sites in the contralateral hemisphere. We conclude that in the AC there are several subtypes of neurons projecting to the contralateral hemisphere; it would be of interest whether these anatomical differences are manifested by physiological differences.

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Unlike the visual and somatosensory areas, where interhemispheric inputs are addressed to the boundaries between areas and vicinities (see above), callosal connections are widespread across the tonotopically-organized representation of A1 (Code and Winer, 1986, 1985; Hackett and Phillips, 2011) and connect tonotopic regions with corresponding frequency domains across the hemispheres (Diamond et al., 1968; Imig and Brugge, 1978; Lee and Winer, 2008; Rouiller et al., 1991). Homotopic interactions have also been established anatomically in rats (Cipolloni and Peters, 1983; Rüttgers et al., 1990). In cats, combined anatomical and electrophysiological experiments revealed a complex pattern of interhemispheric connections, since CPNs and terminals were preferentially distributed over regions exhibiting binaural summation or ipsilateral dominance and suppression, rather than in regions of monaural contralateral responses or contralateral dominance and suppression (Imig and Brugge, 1978).
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The current model of cortical connectivity predicts the various effects observed in the present study (AI→AII, AII→AI and AI→PAF). However, it is important to acknowledge that indirect cortico-thalamo-cortical as well as transcallosal connections may be involved in the observed phenomena (Diamond et al., 1968; Winer et al., 1977; Imig and Brugge, 1978; Andersen et al., 1980; Calford and Aitkin, 1983; Code and Winer, 1985; Ruttgers et al., 1990; Rouiller et al., 1991; Morel et al., 1993; Bordi and LeDoux, 1994; Clasca et al., 1997; Lee and Winer, 2008a). Future experimentation will be required to dissociate the mechanisms by which neuronal deactivation in one area directly or indirectly modulate changes in correlations levels in other regions of cortex.
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^*: Present address: Institute of Anatomy, University of Lausanne, Lausanne, Switzerland.

^**: Present address: Department of Neurobiology, Stanford University School of Medicine, Stanford, CA 94305, U.S.A.

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Commissural connections between the auditory cortices of the rat

Abstract

Brain Research

Hear. Res.

Brain Research

Brain Research

Exp. Neurol.

Brain Research

Brain Research

Brain Research

Neuroscience

Neurosci. Lett.

Brain Res. Rev.

Callithrix jacchus, Brain Reserach

Brain Research

Organization of corticocortical connections in the parietal cortex of the rat

J. Comp. Neurol.

The callosal system of the superior parietal lobule in the monkey

J. Comp. Neurol.

The bilaminar and banded distribution of the callosal terminals in the posterior neocortex of the rat

Brain Research

The neocortical projections to the inferior colliculus in the rat

Anat. Embryol.

Postnatal development of auditory callosal connections in the kitten

J. Comp. Neurol.

Auditory cortico-cortical connections in the owl monkey

J. Comp. Neurol.

Layer V in rat auditory cortex: projections to the inferior colliculus and contralateral cortex

Hear. Res.

Origin of interhemispheric fibers in acallosal opossum (with a comparison to callosal origins in the rat)

J. Comp. Neurol.

Homotopic and heterotopic callosal afferents of caudal inferior parietal lubule inMacaca mulatta

J. Comp. Neurol.