Corticofugal Modulation of Initial Sound Processing in the Brain

Abstract

The brain selectively extracts the most relevant information in top-down processing manner. Does the corticofugal system, a "back projection system," constitute the neural basis of such top-down selection? Here, we show how focal activation of the auditory cortex with 500 nA electrical pulses influences the auditory information processing in the cochlear nucleus (CN) that receives almost unprocessed information directly from the ear. We found that cortical activation increased the response magnitudes and shortened response latencies of physiologically matched CN neurons, whereas decreased response magnitudes and lengthened response latencies of unmatched CN neurons. In addition, cortical activation shifted the frequency tunings of unmatched CN neurons toward those of the activated cortical neurons. Our data suggest that cortical activation selectively enhances the neural processing of particular auditory information and attenuates others at the first processing level in the brain based on sound frequencies encoded in the auditory cortex. The auditory cortex apparently implements a long-range feedback mechanism to select or filter incoming signals from the ear.

Effect of Auditory Cortex Deactivation on Stimulus-Specific Adaptation in the Medial Geniculate Body

“…Furthermore, we demonstrate that the AC modulates the latency of the MGB neurons, mainly shortening their latencies, as previously shown in some subcortical neurons using electrical stimulation of AC (Luo et al, 2008). This effect becomes less pronounced as the neuronal adaptation increases.…”

Selective Subcortical Enhancement of Musical Intervals in Musicians

“…Our results also underscore the role that long-term experience plays in shaping basic auditory encoding and the link between sensory function and repeated exposure to behaviorally relevant signals (Saffran, 2003;Saffran et al, 2006). This tuning of the subcortical auditory system is likely mediated by the corticofugal pathway, a vast track of descending efferent fibers that connect the cortex and lower structures (Suga et al, 2002;Winer, 2005;Kral and Eggermont, 2007;Luo et al, 2008). In the animal model, the corticofugal system works to fine-tune subcortical sensory receptive fields of behaviorally relevant sounds by linking learned representation and the neural encoding of the physical acoustic features (Suga et al, 2002).…”

Musical Experience Limits the Degradative Effects of Background Noise on the Neural Processing of Sound

“…We can also interpret these data within the framework of corticofugal modulation in which cortical processes shape the afferent auditory encoding via top-down processes. It is well documented that the auditory cortex sharpens the subcortical sensory representations of sounds through the enhancement of the target signal and the suppression of irrelevant competing background noise via the efferent system Zhang et al, 1997;Luo et al, 2008). The musician's use of fine-grained acoustic information and lifelong experience with parsing simultaneously occurring melodic lines may refine the neural code in a top-down manner such that relevant acoustic features are enhanced early in the sensory system.…”