Columnar transformations in auditory cortex? A comparison to visual and somatosensory cortices.

Auditory cortical columns have been studied for decades, but intracolumnar processing in auditory cortex is still poorly understood, relative to what is known about such processing in visual cortex and somatosensory cortex. While there are certainly striking similarities in cortical structure across the modalities, investigations of auditory cortex anatomy and synaptic physiology have also found important differences from the columnar organization of other sensory cortices. In vitro and in vivo studies of thalamocortical transformations in the auditory system have begun to reveal the functional significance of these differences, and have defined the earliest stages of auditory cortical processing. However, the question of what transformations are performed within auditory cortical columns remains unresolved. Attempts to find laminar differences in auditory cortex, which could provide the key to understanding columnar transformations, have so far produced contradictory and inconclusive results. Direct analogies to primary visual and somatic sensory cortices would suggest that response properties such as bandwidth, inhibitory sideband structure, preferred modulation rate and modulation phase sensitivity might vary across layers in auditory cortex. While such analogies could prove useful as guidelines for future research, the best hope for understanding auditory columnar transformations may lie instead with a more modality-specific, functional approach.