As the signal travels up the afferent auditory pathway, auditory information is directed to the auditory cortex which is located on the upper part of the temporal lobe. The auditory cortex is subdivided into the primary auditory cortex and other belt areas. The primary cortex contains a precise spatial arrangement of where the sounds are processed in the brain (tonotopic organization).
The acoustic stimulus has already been organized tonotopically along the length of the basilar membrane in the cochlea (see How We Hear). This organization continues in most of the ascending auditory structures between the cochlea and the cortex.
Within the primary cortex is also a striped arrangement that contributes to binaural hearing. The neurons in one stripe are excited by both ears (and are therefore called EE cells), while the neurons in the next stripe are excited by one ear and inhibited by the other ear (EI cells). The EE and EI stripes alternate.
The sorts of processing that occur in the belt areas of the auditory cortex are not well understood, but they are believed to be important to higher-order processing of natural sounds, including those used for communication. It appears that some areas are specialized for processing combinations of frequencies, while others are specialized for processing modulations of amplitude or frequency.