Figure 6.2. The ascending auditory pathway
The figure shows the cochlea, the cochlear nerve, and the levels of auditory processing.
Levels in the brain stem: (1) the cochlear nucleus, dorsal and ventral part; (2) the superior olive; (3)
the lateral lemniscus; (4) the inferior colliculus. In the thalamus: (5) the medial geniculate body. In the
cortex: (6) A I, the core area of the auditory cortex. See also Figure 3.2.
(Brodal 2010:248)
(4) Integration and differentiation: The inferior colliculus (IC) collects information from all lower audi-
tory nuclei. The IC contains several areas with different functions. It projects to the medial geniculate
body (MGB) in the thalamus.
One area of the inferior colliculus displays a sharply tuned response^14 to auditory input. It proj-
ects to the MGB in a tonotopic manner, that is, the frequencies are ordered precisely from high to
low frequencies. Another area of the IC displays a more broadly tuned response to auditory informa-
tion. It contributes to multisensory integration. It projects to the MGB and to the superior colliculus,
which integrates auditory and visual information.
Studies by Kraus et al. (NM III 2008, pp. 543-557) indicate that pitch, timbre and timing have distinct
representations in the brain stem. These representations can be measured by electrodes on the
scalp (p. 545).
14 Sharply tuned neurons respond to a narrow frequency range. Broadly tuned neurons respond to a wider frequency
range.