Activity-dependent plasticity is essential for the
development and function of the nervous system. In mammalian
cortex, sensory stimuli play crucial roles in shaping
the neuronal circuitry and function, and such plasticity
may be largely mediated by activity-dependent synaptic
modification. Although at each level—synaptic, circuitry,
and functional—cortical plasticity has been studied
extensively, the causal relationship between activity-induced
modifications at different levels remains to be firmly
established. The goal of Dr. Dan’s research is to bridge
our understanding of cortical plasticity at these levels.
In his talk he described his studies in the past several
years on stimulusinduced functional modification in
the visual cortex that is believed to be mediated by
spike-timing dependent plasticity (STDP) of intracortical
connections. In STDP, the direction and magnitude of
synaptic modification depend on the relative timing
of pre- and postsynaptic spiking.
In the first part, Dr. Dan described the studies done
in visual cortical slices, where they characterized
the basic STDP learning rule, how it depends on the
dendritic location of the synaptic inputs and how complex
patterns of spiking activity determine the direction
and magnitude of synaptic changes. His studies have
also shed some light on the cellular mechanisms underlying
this form of synaptic plasticity.
In the second part, he described his attempts to explore
the functional significance of STDP in vivo. His experiments
include pairing visual and electrical stimulation in
the rat visual cortex and using precisely timed visual
stimulation to induce changes in visual cortical processing
in the rat. In exploring how STDP interact with visual
stimuli in the natural environment, they found a novel
interaction between motion and position in cortical
neurons’ receptive field, which can explain a well-known
visual illusion in human. Finally, Dr. Dan discussed
his recent work on the effect of natural scenes in shaping
cortical response properties.
