Nature 457, 187-190 (8 January 2009) | doi:10.1038/nature07467
Neural processing of auditory feedback during vocal practice in a songbird
Georg B. Keller & Richard H. R. Hahnloser
Abstract
Songbirds are capable of vocal learning and communication and are
ideally suited to the study of neural mechanisms of complex sensory and
motor processing. Vocal communication in a noisy bird colony and vocal
learning of a specific song template both require the ability to
monitor auditory feedback to distinguish self-generated vocalizations
from external sounds and to identify mismatches between the developing
song and a memorized template acquired from a tutor. However, neurons
that respond to auditory feedback from vocal output have not been found
in song-control areas despite intensive searching. Here we investigate
feedback processing outside the traditional song system, in single
auditory forebrain neurons of juvenile zebra finches that were in a
late developmental stage of song learning. Overall, we found similarity
of spike responses during singing and during playback of the bird's own
song, with song responses commonly leading by a few milliseconds.
However, brief time-locked acoustic perturbations of auditory feedback
revealed complex sensitivity that could not be predicted from passive
playback responses. Some neurons that responded to playback
perturbations did not respond to song perturbations, which is
reminiscent of sensory-motor mirror neurons. By contrast, some neurons
were highly feedback sensitive in that they responded vigorously to
song perturbations, but not to unperturbed songs or perturbed playback.
These findings suggest that a computational function of forebrain
auditory areas may be to detect errors between actual feedback and
mirrored feedback deriving from an internal model of the bird's own
song or that of its tutor. Such feedback-sensitive spikes could
constitute the key signals that trigger adaptive motor responses to
song disruptions or reinforce exploratory motor gestures for vocal
learning.
Nature 457, 205-209 (8 January 2009) | doi:10.1038/nature07520
The dynein regulatory complex is required for ciliary motility and otolith
biogenesis in the inner ear
Jessica R. Colantonio, Julien Vermot, David Wu, Adam D. Langenbacher, Scott
Fraser, Jau-Nian Chen & Kent L. Hill
In teleosts, proper balance and hearing depend on mechanical sensors in the
inner ear. These sensors include actin-based microvilli and microtubule-based
cilia that extend from the surface of sensory hair cells and attach to
biomineralized 'ear stones' (or otoliths)1. Otolith number, size and placement
are under strict developmental control, but the mechanisms that ensure otolith
assembly atop specific cells of the sensory epithelium are unclear. Here we
demonstrate that cilia motility is required for normal otolith assembly and
localization. Using in vivo video microscopy, we show that motile tether cilia
at opposite poles of the otic vesicle create fluid vortices that attract
otolith precursor particles, thereby biasing an otherwise random distribution
to direct localized otolith seeding on tether cilia. Independent knockdown of
subunits for the dynein regulatory complex and outer-arm dynein disrupt cilia
motility, leading to defective otolith biogenesis. These results demonstrate a
requirement for the dynein regulatory complex in vertebrates and show that
cilia-driven flow is a key epigenetic factor in controlling otolith
biomineralization.
Enjoy!
Xiao
XIAO, Jianqiang, Ph.D.
Research Associate
Psychology Department
Rutgers University
152 Frelinghuysen Road
Piscataway, NJ 08854
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