The auditory template theory, first formulated by Konishi in 1965, is central to neurobiological studies of birdsong learning. Young songbirds - the theory posits - first memorize a song model (acquired template) during a sensory phase; subsequently, during a sensory-motor phase, they gradually match their own vocalizations to the memorized template using auditory feedback as an error correction mechanism. Where and how this particular memory is encoded, stored and retrieved in the songbird brain has remained elusive.

The auditory forebrain, including the song system, is the territory whose exploration is most likely to yield clues with respect to template formation and localization. Current research is debating whether the tutor song memory is primarily encoded within some of the song control nuclei (e.g. Drs. Kathy & Ernest Nordeen) or within high-order auditory areas located outside the song system (e.g. Dr. Johan Bolhuis). Conceivably, the acquired template may also be represented in a dynamic fashion within neuronal ensembles distributed across both circuits. One approach is to search for cells that acquire selective responses to the tutor song early in development i.e., prior to the sensory-motor phase of song learning.

Right (With permission from Annals of the New York Academy of Science) A series of autoradiograms showing incorporation of radio-labeled 2-deoxyglucose in the brain of a juvenile zebra finch following a 45min presentation of the tutor song to which the young bird had been exposed previously. Regions of increased metabolic activity include primary and secondary forebrain auditory areas as well as ascending auditory relays, such as the dorso-lateral mesencephalic nucleus (MLD) in the midbrain.

Preliminary recordings in the HVC and the underlying shelf of zebra finch fledglings that have not yet sung (aged 21-23 days) have identified single units (and small clusters of neurons) that fire vigorously to playback of the tutor song relative to other auditory stimuli. Arguably, this finding represents the earliest emergence of selectivity for tutor song in the songbird brain. It builds upon recent work from Dr. Teresa Nick's laboratory showing, early in the sensory-motor phase, increased sensitivity of HVC neurons to the tutor song in the awake, behaving bird. Work in progress in Dr. Daniel Margoliash's laboratory will characterize further the selective properties of these neurons and their distribution within these two nidopallial areas.



A | Some neurons in the HVC-shelf region of the nidopallium are strongly activated by the father's song and respond only weakly to a large spectrum of both natural and artificial auditory stimuli, including songs of the same species.
B | Single unit sharply tuned to the father's song. During playback, the cell discharged bursts of spikes that coincided with specific portions of the song motif. Note alignment of bursts across consecutive presentations of the stimulus.
C | Caudal forebrain of a 20 day-old zebra finch (sagittal section) reacted for cytochrome oxidase (CO). Note increased CO metabolic activity in HVC, L2b, NIf and caudal mesopallium. The sketch highlights the HVC-shelf region (shaded) of the nidopallium where electrodes were advanced.

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