Figure 6.3. Schematic diagram of the ascending auditory pathway (black arrows) and the descend-
ing auditory pathway (red arrows).
Similar to Figure 6.2, the diagram shows the levels of auditory processing: (1) the cochlear nuclei,
(2) the superior olivary complex, (3) the lateral lemniscus, (4) the inferior colliculus, (5) the medial
geniculate body in the thalamus, (6) the auditory cortex.
(Courtesy of the MRC Institute of Hearing Research)
6.3.2. The descending auditory pathway.
The descending pathway reaches all levels of auditory processing from the cortex to the cochlea. It
performs important functions, modifying the upward flow of information and influencing the neural
processing at lower levels. Direct projections descend from the auditory cortex to all levels of the au-
ditory system (Figure 6.3). Three systems are active, a tonotopic system related to the core area, a
diffuse or non-tonotopic system related to the belt area, and a multisensory system, related to wide-
spread areas of the auditory association cortex.
The thalamus
Each area in the auditory cortex project to several nuclei in the thalamus. Some projections form
reciprocal loops between the thalamus and the cortex. It is hypothesized that such loops may func-
tion as a dynamic filter for auditory attention, which permits focusing on a particular sound source or
speaker (He & Yu 2010:264-265).
The inferior colliculus
The tonotopic, the diffuse, and the polysensory systems interconnect the auditory cortex with the IC.
The functional roles of the three systems are not precisely understood.
The superior olive and the cochlea
The superior olive consists of many nuclei. The complex functions of this system exert impact on the
hair cells in the cochleas. This impact may result in the amplification of particular frequency ranges,
and contribute to the focusing on a sound source in a noisy environment.