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Re: pitch neurons

Israel Nelken asked:

> why is there such a pressure
> to assume low-level representation (i.e. subcortical) of pitch?

Dear Eli and List,

the reason why physiological research focused on the exploration of
subcortical mechanisms when looking for the pitch detector simply was that
psychoacoustic data demanded a spectrotemporal mechanism. This ruled out the
auditory cortex, because phase-coupling to pitch-relevant harmonics does not
occur there. The highest level where it occurs is the auditory midbrain.

During the past 15 years all necessary elements for pitch extraction have
been found in the auditory midbrain (inferior colliculus, in the upper
brainstem). Arrays of best-pitch neurons filter out the pitch frequency of
complex sound signals, in the same way as arrays of best-frequency hair
cells filter out spectral frequencies in the cochlea. Whereas the tuning
properties of hair cells in the cochlea are mechanical and electrical, the
tuning properties of pitch neurons are purely electrical. These neurons have
tuned membrane potential oscillations, which are either intrinsic, due to
unit-specific distribution of membrane channel types, or imported from input
neurons. This last question is still an open one.


Martin Braun
Neuroscience of Music
S-671 95 Klässbol
e-mail: nombraun@post.netlink.se
web site: http://hem.netlink.se/~sbe29751/home.htm