2003 Finalist Dr. Karel Svoboda

Dr. Karel Svoboda grew up in the Czech Republic and Germany, and he received his bachelor's degree in physics in 1988 from Cornell University in New York. As a graduate student in biophysics at Harvard University in Massachusetts, he measured the tiny steps and forces produced by individual kinesin molecules. After being awarded his PhD in 1994 he pursued postdoctoral work at Bell Laboratories, where his interests shifted to synaptic and dendritic function and plasticity. In 1997 Dr. Svoboda started his own laboratory at Cold Spring Harbor Laboratory in New York. Work in his laboratory focuses on experience- and activity-dependent plasticity in the cortex, probed with imaging, physiological, and molecular tools.

Imaging experience-dependent synaptic plasticity in the adult neocortex in vivo.
Cortical neural circuits support our stable view of the sensory world. However, the cortex also subserves learning and memory, which indicates that it is continuously fine-tuned by experience, even in adult animals. What is stable and what is plastic in cortical circuits? Our approach is to directly image the mechanisms of experience-dependent plasticity at the level of single synapses in vivo. We find that in the adult mouse barrel cortex the large-scale structure of dendrites and axons is stable over months. Similarly, a large fraction (> 50%) of dendritic spines, tiny postsynaptic specializations, are stable. However, a striking finding was that a subset of dendritic spines (~ 20%) disappeared within a day, to be replaced by other spines. What is the implication of spine addition and subtraction for the plasticity of cortical circuits? Ultrastructural analysis revealed that new spines make synapses; therefore, spine formation and retraction is associated with synapse formation and elimination, respectively. Induction of experience-dependent plasticity increased the turnover of synapses, coincident with a change in receptive field structure. Thus synapse formation and elimination contribute to the experience-dependent rewiring of adult cortical circuits in vivo.

For Dr. Svoboda’s full essay, see Science Online at sciencemag.org.