Inferior colliculi
The colliculi inferiores ("lower hillocks", singular colliculus inferior ; in animals Colliculi caudales - "rear hillocks"; from Latin collis "hill") are the two lower (rear) hills of the midbrain roof ( tectum mesencephali ). Together with the upper mounds ( Colliculi superiores ) they form the four-mound plate ( Lamina quadrigemina or Lamina tecti ).
The inferior colliculus is a central part of the mammalian auditory system . The nerve cells ( neurons ) of the inferior colliculi receive stimulating and inhibiting impulses from neurons in the lower-lying nuclei of the auditory pathway (including the cochlear nucleus and the superior olivar nucleus ) as well as back projections from the auditory cortex . The central areas of the inferior colliculi have a tonotopic organization, with the frequency axis running from dorsal (low frequencies) to ventral (high frequencies).
The nerve fibers that come from the lateral lemniscus reach the inferior colliculi and pass over the inferior colliculus brachium to the medial geniculate body , part of the metathalamus . Here they are connected to the last ascending neurons, whose fibers now pull to the transverse temporales gyri .
Since the fibers are sometimes crossed and uncrossed, unilateral damage to the inferior colliculus leads to a reduction in the hearing ability of the opposite side, but not to complete hearing loss.
anatomy
The inferior colliculus is divided into three main parts: the central core of the inferior colliculus , dorsal (posterior) cortex of the inferior colliculus and paracentral (peripheral) core area of the inferior colliculus . The central core belongs to the specific ( lemniscale ) part of the auditory pathway, i.e. to the main strand of acoustic information processing. The other two main parts belong to the unspecific (extralemniscale) part of the auditory pathway, in which auditory and non-auditory information is combined.
In the central core, the neurons and the catchment area of their dendrites are arranged in layers ( laminae ). In the surface of a layer there is a fine scaling according to acoustic frequencies, while from layer to layer there is a coarse scaling at a distance of about a quarter of an octave .
function
The inferior colliculus integrates almost all of the information from the lower-lying auditory core areas of the brain stem . These include the results of vertical directional hearing from the cochlear nucleus on both sides and horizontal directional hearing from the superior olive (nucleus olivaris superior) on both sides.
According to a theory that has been widely advocated over the last few decades, the central core of the inferior colliculus also determines the pitch of the fundamental tone of complex tones, such as animal sounds, vowels and tones of musical instruments. It is assumed here that the lower harmonic partials of the complex tones are isolated in the frequency band layers (laminae) and that the matching periodicity of the signals of several laminae is filtered out by neural periodicity detectors.
Individual evidence
- ↑ Xiaoqin Wang, Daniel Bendor: Pitch . In: Adrian Rees, Alan Palmer (eds.): The Oxford Handbook of Auditory Science: The Auditory Brain , Oxford University Press 2010, ISBN 0-19-923328-4 , pp. 149–172, here pp. 157–159, 580 pages.