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 Neural
plasticityand its roles in the modulation of behavior.
The primary function of the nervous system is to enable behavioral
adaptation to the environment. Neural plasticity underlies adaptation.
Thus, understanding the nervous system requires a comprehensive
knowledge of neural plasticity. Behavioral, systems, cellular, and
molecular aspects of various forms of plasticity, such as development
and learning, have been examined in thousands of studies. Yet, the
basic mechanisms underlying the modification of behavior are not
well-understood. Only a combination of approaches used in parallel
will reveal the complex relationships of brain and behavior.
My laboratory uses a vertebrate model, the songbird, in the study
of neural mechanisms of behavioral modulation. As in mammals, the
forebrain of birds contains neural control areas such as the thalamus,
basal ganglia, limbic system (e.g. hippocampus), and a cortex homolog.
The song system is a dedicated neural circuit that includes cortical
nuclei. Its discrete, nuclear structure enables precise excision
and manipulation of functional units in a complex network. Further
strengths of this system are that (1) the song behavior is easily
recorded and analyzed; (2) the learning of song follows a well-established
time-course; (3) the acquisition of the song behavior can be manipulated
easily; and (4) the anatomical development of the song system occurs
in parallel with the development of song. Thus, the songbird is
a preparation that can be examined with top-down and bottom-up approaches.
We use a combination of techniques ranging from spectral analysis
of song behavior to whole-cell patch clamping of neurons to test
hypotheses regarding the control of neural activity and its relationship
to behavior.
We are currently focused on the song nucleus HVC (also known as
the High Vocal Center). This nucleus processes both sensory and
motor information. The figure below shows HVC activity in a finch
in the process of learning song. The auditory response to playback
of the song of the bird's tutor (green) is followed by premotor
activity that drives the bird's vocal organ to call (arrow). We
have found that, at a critical period in song development, HVC neurons
exhibit state-dependent selective activation by a learned tutor
song. This represents the first evidence of a 'memory trace' in
the premotor song system.
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