Redwood Neuroscience Institute
Title: Spatial representation of pitch: the 2nd neural axis
of the auditory system
Abstract:
Harmonic sounds, particularly
voiced speech sounds and animal communication signals, are characterized by
periodic envelope or amplitude modulations. Periodicity information is coded in spike intervals in the auditory
nerve and by different temporal response patterns in the nucleus cochlearis. We suggested a neuronal model that utilizes
these temporal informations for a correlation
analysis of signal periodicity in the assuming delayed responses and
coincidence of delayed and undelayed responses as
basic processing elements.
We found units in the
auditory midbrain which were to tuned not only to a certain frequency, but also
to different modulation frequencies with a spatial distribution resulting in
topographic maps for a wide range of modulation frequencies. In addition, evidence
for similar maps in the auditory cortex comes from optical recording in cat,
2-deoxyglucose mapping in gerbils and magnetoencephalography in humans. In summary, periodicity
is mapped from midbrain to cortex. Since the main gradients of tonotopic and periodotopic
organization are orthogonal to each other, the periodotopic
axis may be considered as the 2nd neural axis of the auditory
system.