Cortical maps for hearing and egocentric selection for self-organization

The auditory cortex of the mustached bat shows complex multiple frequency maps, because cortical neurons in several areas are tuned to particular combinations of signal elements. Different types of combination-sensitive neurons form computational maps in which information-bearing parameters for echolocation (biosonar) are represented systematically. Neuronal response properties and multiple-frequency and computational maps were considered to be created solely by divergent-convergent interactions of neurons in the 'ascending' system. However, we have found that the 'corticofugal' system also plays an important role. Neurons in an iso-best frequency (or echo delay) 'minicolumn' of the auditory cortex augment the auditory responses of subcortical neurons tuned to that frequency (or echo delay) and sharpen their tuning. At the same time, they reduce the response and shift the tuning of subcortical neurons tuned to other frequencies (or echo delays) away from the best frequency (or delay) of the cortical neurons. Cortical neurons mediate a highly focused positive feedback, incorporated with widespread lateral inhibition, via corticofugal projections. This 'egocentric selection' is expected to play an important role in self-organizing the central auditory system.