A complex tone code in the auditory cortex

In the search for an objective measure of a biologically meaningful encoding scheme for cochlear implants, we recorded responses to tones from the alert auditory cortex. Neurons in the primary auditory field (A1) are typically characterized by filter characteristics resembling those of eighth nerve afferent fibers (filter neurons). In contrast, a different class of neurons has been found thus far only outside of the cochleotopic A1 array. These cells are sharply tuned to pure tones, and corresponding fundamental frequencies of harmonic complexes (F0 neurons). Thus these cells are specific for various tones of the same pitch. Sharpened pure- and complex-tone tuning can be accounted for by lateral inhibition. Time patterns for tonal and noise responses can vary dramatically.