WHO:	Luisa Scott , Neuroscience Thesis Defense
TOPIC:	Mechanisms of Neural and Vocal Plasticity in the Adult Song Bird
ABSTRACT:	While all songbirds experience an early postnatal period of auditory-dependent song development, many also use auditory feedback to shape adult vocalizations. Even species that normally produce fixed song patterns in adulthood experience song degradation in the absence of acoustic input. This work explores possible mechanisms through which the removal of auditory feedback alters the motor program encoding song. One source for behavioral drift in the absence of feedback may be the ongoing addition of vocal-motor neurons. Low levels of HVC (a premotor nucleus necessary for song production) neuron incorporation persist in a species that relies upon auditory cues to maintain stable adult song, and incorporating these new HVC neurons in a behaviorally conservative manner could require sensory feedback. However, eliminating a nucleus necessary for vocal plasticity, the lMAN, restricts song degradation after deafening. lMAN lesions must modulate vocal plasticity by affecting HVC neuron addition if the addition of new neurons is sufficient for deafening-induced behavioral change. These ideas were tested by labeling new HVC neurons with [3H]thymidine. An inter-species comparison revealed a positive correlation between the rate of song degradation after deafening and HVC neuron addition. In contrast, lMAN lesions did not reduce the proportion of newly added HVC neurons surviving for several weeks or months in adult, deaf birds, but these lesions did restrict vocal change. Thus, HVC neuron addition alone does not instigate the requirement for auditory feedback in adult song maintenance. A second vein of research explored whether changes in NMDAR subunit expression underlie song degradation after adult deafening. The NMDAR is important for song learning. Song nuclei also display developmental and adult, seasonal changes in NMDAR modulatory subunit transcription that coincide with the regulation of vocal plasticity. But, in situ hybridization in several key song nuclei revealed that adult deafening does not trigger a recurrence of a more juvenile NMDAR modulatory subunit mRNA expression. These findings show that neither the extent of HVC neuron incorporation nor changes in NMDAR subunit transcription are proximate causes of song degradation after deafening. Nonetheless, direct manipulation of HVC neuron addition could dictate the extent of song degradation after adult deafening.
WHEN:	8/14/2003 1:00:00 PM
WHERE:	Med Center K307 (3-6408)

Events Homepage