With their highly developed sense of hearing, bats hold a special fascination for auditory physiologists. On page 54https://doi.org/www.nature.com/articles/nn0598_54, Yan & Suga examine the role of corticofugal projections in the auditory system in the big brown bat (shown here). As with other mammals, sound stimuli reach the auditory cortex by way of the inferior colliculus (IC) of the midbrain, which in turn receives a large feedback projection from the cortex. The connections between the two areas are tonotopic; the IC contains a map of auditory frequencies, which projects via the thalamus to form a corresponding map in the cortex. But the significance of the reciprocal connections from the cortex to the IC (the corticofugal projection, a common feature of sensory systems) is less well understood. The authors have investigated this question by stimulating the cortex, either electrically or with sounds, and examining the effect on the frequency-selective neurons of the IC. Stimulating the cortex at a given frequency causes shifts in the tuning of IC neurons in the corresponding frequency range. The net effect of these shifts, which persist for at least 30 minutes, is to enhance the midbrain response to the stimulated frequency, while suppressing responses to adjacent frequencies. The authors suggest that one function of the corticofugal system may be to modulate the lower levels of the auditory system in response to auditory experience.
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Jennings, C. Listen up. Nat Neurosci 1, 12 (1998). https://doi.org/10.1038/304