Auditory neurons in the forebrain nucleus HVc (hyperstriatum ventrale
pars caudale) are highly sensitive to the temporal structure of the
bird's own song. These ``song-specific'' neurons respond strongly to
forward song, weakly to the song with the order of the syllables
reversed, and little or not at all to reversed song. To investigate
the cellular mechanisms underlying these responses, in vivo
intracellular recordings were made from adult HVc neurons.
Song-specific cells could be divided into those that responded
strongly throughout autogenous song (tonic cells) and those that
responded with bursts of action potentials at specific points during
the song (phasic cells). Phasic cells were hyperpolarized during
autogenous song even though this stimulus also elicited the strongest
response. Less hyperpolarization was seen to the same song with the
syllables in reverse order, and none was seen to reversed song. The
responses of both types of song-specific cells contained high
frequency bursts of action potentials. The bursts of the phasic cells
showed attenuation of the action potential height and lack of full
repolarization following each spike. This type of bursting was
significantly correlated with the amount of hyperpolarization prior to
each burst in phasic cells and non-auditory cells that generated such
bursts spontaneously. These data suggest that song-specific neurons
use long-lasting hyperpolarization as a mechanism to integrate
auditory context, an important component of temporal order
selectivity. Hyperpolarization may also increase the precision of
spike timing, which could be important for the neural code subserving
song learning and production.
Postscript unavailable.
Mike Lewicki's home page.