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Marc F. Schmidt, Ph.D.

Click here for selected publications since Dr. Schmidt's arrival at Penn

RESEARCH INTERESTS

RESEARCH TECHNIQUES

RESEARCH SUMMARY

The goal of our research is to understand the functional organization of the circuits that control vocal production, perception and learning. We study these questions in songbirds, which produce highly stereotyped songs that are learned within a restricted phase during the animal's juvenile stage. Our experiments are performed in both awake and anesthetized animals and can be divided into three broad areas.

a. Neural mechanisms of behavioral state-dependent auditory processing and perception
We have shown that auditory responses in forebrain song control nuclei are highly dependent on the animal's behavioral state with auditory responses varying from robust to non-existent depending on the animal's arousal or attentional state. We are presently characterizing the neural mechanism(s) underlying this modulation of auditory responsiveness. We are also combining behavioral experiments with neural recordings in order to characterize behavioral states that are optimal for auditory response tuning in the awake bird.

b. Neural encoding of forebrain vocal motor commands
We are using a combination of extracellular recording and stimulation in awake singing birds to perturb the bird's song output in order to understand the relationship between neural discharge patterns in higher-level forebrain song structures and the bird's vocal output.

c. Neural correlates of vocal ontogeny
Because young bird's can learn their song under carefully controlled tutoring conditions, we are studying the dynamic changes in neural tuning during acquisition of the song template. These studies are aimed both at understanding the mechanism of how the auditory template is stored in these song nuclei as well as how the network properties change during vocal learning.

Figure 1. Example of auditory gating in HVc. In the left panel, an HVc implanted adult male zebra finch is perching in his cage and sounds are being passively broadcast through a speaker. Presentation of the bird's own song (BOS; the preferred auditory stimulus for HVc neurons) fails to elicit any auditory-specific neural responses. The top segment represents the raw neural waveform, the middle segment a cumulative histogram of ten presentations of BOS (30 ms bin size) and the bottom segment the amplitude envelope of BOS. Several minutes after auditory playback in the awake bird, the subject was injected with the anesthetic Ketamine (in combination with Xylazine). As shown in the right panel, presentation of BOS elicited a robust auditory response in HVc in the anesthetized bird. This auditory response was only observed during a short window of time (approximately 30-60 min) after which time the bird started to regain consciousness and auditory responses disappeared.

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