Summary
Single units in the medial genioulate body and inferior colliculus of the cat were activated by acoustic stimulation and their activity was tested by orthodromic conditioning stimulation of the auditory cortex with the following findings;
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1.
Two groups of the cells in the medial geniculate body and the inferior colliculus, activated by both cortical electric stimulation and tonal stimulation, have been classified as „modification” units and “no modification” units.
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2.
Corticofugal stimulation inhibited or facilitated “modification” units. “No modification” units were subdivided into a) units with no electrical response, b) units with independent responses to both auditory and electrical stimulation, c) units with electrical response only. These were believed to be, respectively, principal neurons, inhibitory interneurons and excitatory (efferent) interneurons.
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3.
In general, fibers from AI elicit inhibitory while those from AII elicit facilitatory effects in the medial geniculate body.
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4.
Cortical stimulation produced a threshold change on the response area of “modification” units.
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5.
It is concluded that a number of, not very many, centrifugal fibers innervate the ipsilateral geniculate neurons.
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6.
In agreement with anatomical findings, physiological evidence suggests that corticofugal fibers from both auditory cortices innervate inferior colliculus neurons. Their modification patterns were same as those of geniculate units except the latency of responses was much longer.
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7.
A centrifugal control mechanism may play an important role in the frequency selective gating mechanism of the central auditory system.
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Watanabe, T., Yanagisawa, K., Kanzaki, J. et al. Cortical efferent flow influencing unit responses of medial geniculate body to sound stimulation. Exp Brain Res 2, 302–317 (1966). https://doi.org/10.1007/BF00234776
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DOI: https://doi.org/10.1007/BF00234776