INSERM EPI 9926, Laboratoire de Neurophysiologie et Neuropsychologie, Faculté de médecine, 13005 Marseille, France
Address for correspondence: Catherine Liégeois-Chauvel, INSERM EPI 9926, Laboratoire de Neurophysiologie et Neuropsychologie, Faculté de médecine, 27 Bd. Jean Moulin. 13005 Marseille, France. Voice: +33 4 91 32 44 63; fax: +33 4 91 78 99 14.
catherine.liegeois{at}medecine.univ-mrs.fr
One acoustic feature that plays an important role in pitch perception
is frequency. Studies on the processing of frequency in the
human and animal brain have shown that the auditory cortex is
tonotopically organized: low frequencies are represented laterally
whereas high frequencies are represented medially. To date,
the study of the functional organization of the human auditory
cortex in the processing of frequency has been limited to the
use of either scalp-recorded auditory evoked potentials (AEPs),
which have relatively poor spatial resolving power, or functional
imagery techniques, which have poor temporal resolving power.
The present study uses intracerebrally recorded AEPs to explore
this topic in the primary and secondary auditory cortices of
both hemispheres of the human brain. Recordings were carried
out in 45 adult patients with drug-resistant partial seizures.
In the right hemisphere, clear spectrally organized tonotopic
maps were observed with distinct separations between different
frequency-processing regions. AEPs for high frequencies were
recorded medially, whereas AEPs for low frequencies were recorded
laterally. In the left hemisphere, however, this tonotopic organization
was less evident, with different regions involved in the processing
of a range of frequencies. The hemisphere-related difference
in the processing of tonal frequency is discussed in relation
to pitch perception.
