Tuesday, January 31, 2012
Interaction of Planning Areas in Cerebral Cortex
R. Chess Stetson, Computation & Neural Systems, California Institute of Technolgoy
How do cortical areas interact as a monkey plans a movement? We seek to answer this question using timing relationships between action potentials and local field potentials (LFPs) as a monkey plans reaches and eye movements to remembered targets. Both parietal reach region (PRR) and dorsal premotor cortex (PMd) show similar spiking activity characteristic of reach planning, though they are located in completely different parts of the brain. After an instruction to reach or saccade to a spatial target, 53% of PRR cells and 62% of PMd cells code for the future action. Even when the animal can freely decide on his action, both parietal and premotor cells predict the upcoming movement seconds before it occurs. Yet despite their apparent similarity in single neuron activity, they interact asymmetrically. PMd responds to outside stimuli tens of milliseconds before PRR, yet during periods of steady state PRR appears to drive PMd. Coherent phase-locking between action potentials and local field potentials (LFPs), which has been implicated in directional influence between brain regions, is highly significant from PRR to PMd (>40% of cells), but not vice-versa (<5%). This uni-directional spike-LFP coherence, strongest at 15-25Hz, varies over the course of the trial, achieving a peak in magnitude and frequency, on average, during the planning period. The PRR-PMd interaction varies with the planned behavior, and is stronger between anatomically connected regions than unconnected ones. These results suggest a frequency-dependent interaction between frontal and parietal regions that balances influence between different phases of action planning.