Peripheral auditory input to the midbrain limbic area and related structures.

The effect of peripherally applied auditory stimulation on unit activity in midbrain limbic and related regions was investigated in the freely behaving rat. Two pure tones (1 and 10 kHz) and a noise generated by the discharge of a solenoid were used as stimuli presented randomly with 1 min mean interval between presentations. Computer-aided analysis of unit activity indicated that (1) a high proportion of neurons in the limbic midbrain region give excitatory responses to the three stimuli; (2) a majority of the responses have short latencies, especially in the dorsal raphe nucleus; (3) frequency and physical properties of the stimuli seemed not crucial for eliciting responsiveness; (4) habituation to repeated presentation of stimuli was not characteristic of the excitatory responses in the limbic midbrain region. These results are discussed in the light of possible functions of this region.