聴性脳幹反応と下丘

Abstract

The role of the inferior colliculus (IC) to the auditory brainstem response (ABR) was investigated in rats by the following experiment consisting of; (1) observation of change in the ABRs and evoked potentials (EPs) of the IC before and after unilateral destruction of the cochlea. (2) observation of change in the wave form of EPs and ABRs before and after destruction of the IC. (3) recording of the EPs at various points in and around the IC. (4) search for the isopotential line in and around the IC. (5) recording of EPs to electrical stimulation of the IC. The EP of the central nucleus of the IC consists of one or two positive waves followed by a large negative wave. The wave form of the ABR seems to be a composite of a positive slow wave and several sequential fast wave-lets, and characteristics and origins of these two potentials are different to each other.The central nucleus of the IC is more important for generation of the positive slow component. A negative field is observed in the central nucleus of the IC, and a positive field surrounding this negative field is recorded as the positive slow wave of the ABR from the surface of the brain. A similar electrical potential field was also observed by the direct electrical stimulation of the IC, that is, a large negative potential was recorded at the central nucleus of the IC and a positive potential was observed at the surface of the brain, when the lateroventral part of the IC were stimulated electrically. Thus, the positive slow wave of the ABR is consisted mainly of this positive potential field, at least in latter part of the slow wave.The central nucleus of the IC might not be essential for generation of the several sequential fast waves of the ABR, because their latencies and amplitudes were not changed by destruction of the central nucleus of the IC. However, when the lesion was extended to or located in the lateroventral part of the IC, where the nerve fibers of the peripheral nuclei penetrate into the IC, potential V and VI were abolished whereas potential IV was remained unchanged. Thus, the structures peripheral to the IC play an important role for the generation of potential IV, and the lateoventral part of the IC is essential for generation of potential V and VI.