Processing abstract auditory features in the human auditory cortex.

Using electric and magnetic brain responses we tested whether violations of an abstract auditory regularity are processed in auditory cortex and whether abstract auditory regularities are retained for at least 10 s. The mismatch negativity (MMN) event-related potential and its magnetic counterpart (MMNm) were recorded to infrequent tone pairs of descending pitch (the second tone having a lower frequency than the first one) embedded in a sequence of tone pairs of ascending pitch, whereas the absolute frequency of both ascending and descending tone pairs varied on seven levels. Results showed that the dominant generators of the electromagnetic activity elicited by violations of the pitch-ascension rule lie within auditory cortex. We also found that the memory representation of pitch-ascension is retained for at least 10 s. When short trains of ascending-pitched tone pairs were followed by a silent period of 8-12 s, descending-pitched probe tone pairs elicited the MMN component when a single reminding pair with ascending pitch was presented before the probe. The reactivating effect of the reminder was similar to what has been previously shown for concrete auditory regularities, such as the constancy of tone pitch. The present results support the view that auditory cortical functions can process sensory and categorical information in a similar manner.