Tonotopic organization of the auditory brain regions can be demonstrated by creating maps of activity associated with different frequencies. Here, each animal was injected with the metabolic tracer 2-deoxyglucose (2-DG) and then exposed to a tone of a particular frequency. Because 2-DG is taken up like glucose by neurons, but not metabolized, we can use its presence within neurons as an indicator of neuronal activity. Postmortem processing of 2-DG distribution reveals which cells were most active when the stimulus frequency was presented (see Figure 1).
Most species of animals have several auditory cortical fields. Different fields of the auditory cortex may be specialized for location of sounds in space, movement of sound sources, perception of species-specific sounds, and so on (see Figure 2). By and large, cortical auditory areas are dedicated to the processing of “biologically relevant” sounds; that is, these regions have been shaped through evolution to be especially responsive to sound patterns that signal threats or opportunities in the environment.
The arrows show the direction of tonotopic representation, from low to high frequencies. (After Merzenich et al., 1993.)
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