The Cognitive Neuroscience of Music

In the primary auditory cortex, no frequency-dependent changes in amplitude or

latency were observed for the earliest components (N13/P17) in either hemisphere. For the

N30, only slight variations in amplitude were seen in response to tonal frequency, and most

often its amplitude covaried with that of the 50-ms component. The amplitude of the

50-ms component was maximal for high frequencies (4 kHz) in medial regions of the pri-

mary cortex and for low frequencies (400–500 Hz) in lateral regions. Both mediolateral and

anteroposterior organizations observed were marked by a progressive decrease in BFs

toward the boundaries of the primary cortex.

The present data suggest the existence of an orderly, tonotopic representation of fre-

quencies in the human primary auditory cortex, similar to that described in nonhuman

animals.13,40In humans, BFs vary from 4 kHz medially to 400 Hz laterally for the 50-ms

component. This range roughly corresponds to the frequency range useful for speech (this

latter range actually begins near 250 Hz—a frequency at which a clear evoked response

was difficult to obtain in this study). Studies exploring the auditory cortex of nonhuman

primates have shed a great deal of light on the functional organization of the human auditory

cortex, because its organization in primates appears to be similar to that in humans. In prim-

ates, BFs are represented in an orderly pattern in the primary auditory cortex and range

from below 100 Hz to about 32 kHz, nearly the full frequency hearing range for primates.

The lowest BFs are represented rostrally and laterally, whereas the highest BFs are found

caudally and medially. Such an organization is thought to cover almost the entire auditory

cortex, with all frequencies (except those at the extreme ends of the frequency hearing

range) being represented.2,16,41,42The BFs observed in the present study were highly stable

162     

N 100

N/P80-100

N/P 50 N/P 50

N/P80– 100

?

HFHF

HF

HF LFLFLF

LF

N/P 30 N/P 30

500 500500

750750

1 K 2 K

1 K^2 K^4 K

500750

1 K^2 K^4 K

4 K

4 K

Figure 10.6Schematic representation of the tonotopic maps recorded from the right and left auditory areas (see
comments in the text).