The middle latency response generating system.

In summary, primary pathways are specifically auditory-sensitive, show fine frequency tuning, and good time-locking. The responses are reliable and show substantial binaural interactions. The primary pathway includes the ventral portion of the medial geniculate and the primary auditory cortex. The animal MLR recorded from over the temporal lobe, the temporal response, has been associated with the primary pathway because it is affected by pharmacological inactivation of MGv and electrolytic lesions of the primary auditory cortex. It is a large, reliable, rate-sensitive response, that shows a relatively late development and high degree of binaural interaction. Non-primary pathways are multimodal, broadly tuned, and show only mild binaural interaction. The midline response is associated with the non-primary areas because it is affected by pharmacologic inactivation of MGcm and mRF, but is not affected by inactivation of MGv or lesions of auditory cortex. The midline response is relatively small, labile, and rate-resistant. It develops early and shows only a small degree of binaural interaction. The generation of MLR thus appears to reflect an interplay of primary and non-primary areas in the auditory thalamo-cortical pathway. The non-primary and primary components may be differentiated in numerous ways: by lesions, by stimulus variations, and topographically. The non-primary components appear to develop early and are probably sleep state dependent, while the primary components develop later and are reliable even in sleep. In young children, it is essential to monitor sleep state in order to obtain reliable recordings, leading us to speculate that the non-primary components dominate the MLR.(ABSTRACT TRUNCATED AT 250 WORDS)