Karel Svoboda, Ph.D.
Howard Hughes Medical Institute
Janelia Farm Research Campus
May 2, 2011

The Cortical Circuits Underlying Object Localization

From the structure of connectivity we move to the level of neuronal circuits. Certainly the most complex of these circuits can be found in the cerebral cortex, the evolutionarily "new" brain in human and animal species. Understanding cortical circuitry offers an answer to some of the most intriguing questions in neuroscience. It is the cerebral cortex that carries our higher-level learning, memory, consciousness and cognition. In his presentation Dr. Svoboda explored one of these questions: how cortical circuits transform sensory input into a behavioral response.

Dr. Svoboda's work focuses on the cerebral cortex, which is the largest part of the mammalian brain. Neocortical circuits within this structure are remarkably similar across functional areas and species and have been shown to play a role in most flexible behaviors. The Svoboda lab attempts to understand the principles that organize neocortical circuits and to decipher how they process information and guide behavior by focusing on the circuitry underlying whisker-dependent somatosensation in mammals.

Mice and other rodents use their whiskers to recognize and determine the locations of objects. Dr. Svoboda's lab has developed quantitative psychophysical methods for tracking the motor strategies and sensory inputs used by mice in whisker-based object localization. At the same time, members of his lab can record from specific neuronal populations using electrophysiological and imaging methods within mapped neural circuits. These measurements have provided hypotheses regarding how activity in specific neurons might drive behavior. In particular, in layer four of the barrel cortex (areas of the rodent brain responsive to single bristles), object location might be coded by the number or timing of action potentials. Experiments utilizing precisely timed photostimulation have shown that mice judge object location via the number of action potentials and disregard precise spike times, two elements underlying this unique behavior.