Corticofugal system and processing of behaviorally relevant sounds : Perspective

The auditory system consists of the ascending and descending (corticofugal) systems. One of the major functions of the corticofugal system is the adjustment and improvement of auditory signal processing in the subcortical auditory nuclei, i.e., the adjustment and improvement of the input of cortical neurons. The corticofugal system evokes a small, short-term reorganization (plasticity) of the inferior colliculus, medial geniculate body and auditory cortex for acoustic signals repetitively delivered to an animal. When these signals become behaviorally relevant to the animal through conditioning (associative learning), the short-term reorganization is augmented and changes into a long-term reorganization of the auditory cortex. Animals acquire the behavioral relevance of sounds through associative learning. Human babies also acquire language through associative learning. Therefore, the corticofugal system is expected to play a particularly important role in processing behaviorally relevant sounds and in reorganizing the auditory cortex according to the behavioral relevance of sounds. Since the ascending and descending systems form multiple feedback loops, the neural mechanisms for auditory information processing cannot be adequately understood without the exploration of the interaction between the ascending and descending systems.