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Marc F. Schmidt, Ph. D.

Associate Professor of Biology
Ph.D., Colorado State University, 1993
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312 Leidy Laboratories
Department of Biology
University of Pennsylvania
Philadelphia, PA 19104 USA

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+1 215 898.9375

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+1 215 898.8780

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marcschm@sas.upenn.edu

research : publications : awards : affiliations : education : teaching:

Main Research Site: http://schmidt.bio.upenn.edu/schm

encoding of complex motor behaviors; auditory feedback and vocal learning

Birdsong has established itself as one of the most powerful model systems for the study of complex learned behaviors. Much of the strength of the system lies in the ease with which the behavior can be quantified and the prominence of the highly specialized nuclei, known collectively as the song system, which are involved in song learning and production. In addition, because song learning in birds and language acquisition in humans are both dependent on auditory feedback, the study of birdsong learning is likely to provide many insights into the mechanisms underlying vocal development in humans. Work in our laboratory is centered on understanding the mechanism(s) underlying vocal learning and can be divided into three main areas: (1) motor organization of the song system, (2) processing of auditory feedback signals and (3) synaptic organization of a key auditory/motor song nucleus. The long-term goal of our laboratory is to understand how the nervous system encodes complex learned motor behaviors, such as song, as well as study how auditory feedback signals shape song motor networks during song learning. To pursue these issues, we use a variety of different techniques, which range from slice physiology to chronic neural recordings in awake singing birds.

organization of the song motor network

The motor pathway for song production consists of a bilaterally symmetrical descending set of pre-motor forebrain nuclei (HVc and RA), which ultimately innervate the motor- or premotor neurons for muscles that control respiration and the vocal organ (Syrinx). By recording neural activity simultaneously in left and right HVc of awake, vocalizing male zebra finches, we have shown that vocal premotor neurons are highly synchronized during specific portions of the song motor response. Because synchronization occurs independently of the recording sites within HVc in either hemisphere, we believe that most HVc motor units are globally synchronized. The lack of direct interhemispheric connections between forebrain song control nuclei (birds do not have a corpus callosum) and the pattern of synchronous activity suggest that each nucleus receives song-specific patterned inputs from thalamus or midbrain:

Schematic illustration of bilateral organization of avian song system. Electrodes were implanted in left and right HVc and neural activity is recorded simultaneously from both sides while the bird is singing. HVc forms part of bilaterally identical motor pathways controlling song production. Interhemispheric connections between song control nuclei are absent at the level of the forebrain, however several bilateral projections situated below the forebrain projecting back to HVc have been described. For clarity, only the bilateral feedback pathway from DM to UVa is shown. DM, dorsomedial nucleus of the intercollicular region; HVc, the acronym is used as the name of this nucleus; Nif, nucleus interfacialis of the neostriatum; RA, nucleus robustus of the archistriatum; Ram, nucleus retroamgualis (controls respiration); nXII, hypoglossal nucleus (tracheosyringeal part controls the syrinx)

These inputs are likely to be critical in determining song parameters related to syllable sequencing and timing and suggest an important role for these input structures in the determination of song structure. We have been investigating, in collaboration with Eric Vu (Barrow Neurological Institute), the nature of interhemispheric synchronization and coordination during singing by combining short stimulation pulses, which disrupt song behavior, with extracellular recordings in HVc (Vu, Schmidt and Mazurek, 1998).

auditory responses in the song system

In addition to its motor properties, HVc also receives direct auditory inputs from the auditory forebrain and acts as a gateway for auditory information flow into the song system. Recordings from anesthetized songbirds have shown that HVc contains some of the most complex auditory neurons known. By directly comparing auditory responses from the same electrode in awake and anesthetized zebra finches, we have shown that HVc auditory neurons are completely suppressed in the awake, behaving animal (Schmidt and Konishi, 1998).

Zebrafinch song motif analysis

(a) Representation of a typical zebra finch song highlighting the highly stereotyped nature of this behavior. A given song bout is typically preceded by one or more introductory notes (i) which are followed by a stereotyped sequence of syllables (S1 --> S4), known as motifs, which are repeated several times (two in this example).

(b) Quantitative representation of synchronization of song premotor activity. Top, Spectrogram of the first motif of a canonical song used as reference to compute the sliding cross correlation. Middle and bottom, Color representation of the sliding cross correlation matrix for song premotor activity for the 1st and 2nd motif (bottom panel). Each cross correlation is normalized to the autocorrelation to show the correlation value r for each cross correlation time lag and cross correlation matrices are color coded to illustrate the different r values with red representing high levels of correlation and blue representing negative r values or values near 0. Comparison of the cross correlation matrix between the first and second motif show that the overall correlation pattern between hemispheres is highly conserved across motifs. Significant cross correlation values (shown in red) occur at or near 0 ms time lag and occur in a discreet syllable specific pattern. Cross correlation matrix for the 1st and 2nd motif both represent the mean from 22 different songs sung over two days.

This unexpected result is of general interest because it suggests that the behavioral state of an animal may play an important role in modulating , in some cases even suppressing, sensory flow into higher cortical areas. In songbirds, the suppression of auditory responses seems to occur within HVc, as it is not observed in auditory input stages to this nucleus. Recent findings in our lab as well as that of Dan Margoliash (Dave et al. (1998) Science 282:2250-2254 ) suggest that sleep can mimic the effect of anesthesia on auditory gating. We are presently investigating the mechanism(s) by which different behavioral states may modulate the opening and closing of this gate. Behavioral states that are of particularly interest to us include sleep, attention as well as the motor act of singing. We are also interested in whether gating is developmentally regulated during song learning. Gating of auditory responses in HVc would prevent young juveniles from storing the song template into song system-specific areas and we hypothesize such gating should be absent in juvenile birds during the early auditory phase of song learning. Understanding the cellular bases of this phenomenon may provide us with insights into the regulatory mechanisms of critical periods during vocal learning.

Schematic illustrating behavioral states (real and hypothesized) that may play a role in the regulation of auditory gating in the avian song system.

synaptic organization of HVc

To begin to analyze possible cellular mechanisms of auditory gating, as well as understand the organization of the vocal motor network, we are characterizing the synaptic organization of HVc. In particular, we are studying how synaptic inputs from known input structures may modulate, or suppress, neural responses in different subtypes of HVc neurons. This work is performed using both sharp and whole cell electrode recording techniques in slice as well as restrained whole animal preparations.



selected publications

Cardin J.A. and M.F. Schmidt (2004) Auditory responses in two sensorimotor forebrain song system nuclei are co-modulated by behavioral state. J. Neurophys. 91: 2148-2163.

Cardin J.A. and M.F. Schmidt (2004) Noradrenergic inputs mediate state dependence of auditory responses in the avian song system. J. Neurosci. 24: 7745-7753.

Cardin, J.A. and M. F. Schmidt (2003) Song system auditory responses are stable and highly tuned during sedation, rapidly modulated and unselective during wakefulness, and suppressed by arousal. J. Neurophysiology 90: 2884-2899.

Schmidt M. F. (2003) Pattern of interhemispheric synchronous premotor activity in HVc correlates with key transitions in the song pattern. J. Neurophysiology 90: 3931-3949.

Nealen P. M. and M. F. Schmidt (2002) Comparative Approaches to Avian Song System Function: Insights into Auditory and Motor Processing. J. Comp. Physiology 188: 929 – 941.

Dutar P., Petrozzino J. J., Vu H.M., Schmidt M.F. and D. J. Perkel (2000) Slow Synaptic Inhibition Mediated by Metabotropic Glutamate Receptor Activation of GIRK Channels. J Neurophys. 84: 2284-2290.

Schmidt M. F. and M. Konishi (1998) Gating of auditory responses in the song control system of awake songbirds. Nature Neuroscience 1: 513-518.

Vu E. T., Schmidt M. F. and M. E. Mazurek (1998) Interhemispheric coordination of premotor neural activity during singing by zebra finches. J. Neurosci. 18(21): 9088-9098.

awards

  • Alfred P. Sloan Foundation Fellow
  • Basil OConnor Award, March of Dimes

professional affiliations

  • Society for Neuroscience
  • American Physiological Society

education

teaching

  • BIOL 251: Cellular Neurobiology
  • BIOL 451: Systems Neuroscience


People
Department of Biology
School of Arts and Sciences
University of Pennsylvania

last updatedSeptember 19, 2009