Gamma-band synchronization in the neocortex: novel analysis methods and their application to sensory and motivational systems

Vinck et al. develop new statistical techniques for the analysis of electrophysiological brain data, and applied these techniques to the study of brainwaves in sensory and motivational systems. Chapter 2 develops a new measure of phase locking between spike trains and Local Field Potentials (LFP) that is unbiased for firing rate and spike count. Chapter 3 develops a new measure of phase synchronization between EEG/MEG/LFP signals that is robust against the effects of volume conduction, noise and sample size bias. Chapter 4 examines the effect of measurement noise on Granger causality statistics, and finds that statistical control using time series reversal provides a viable solution for the noise problem, as opposed to examination of the slope of the coherency function. Chapter 5 develops a new estimator of the entropy function based on polynomial expansion of the entropy function and Bayesian estimation. Chapters 6-8 apply these techniques to experimental spike and LFP data obtained from the awake rat using multi-areal ensemble recordings. Chapter 6 shows (1) the presence of band-limited gamma-band (30-90 Hz) oscillations in the barrel cortex, (2) cell-type-specific entrainment of cells by this gamma rhythm, and (3) absence of gamma phase-coupling with other structures (visual and perirhinal cortex, hippocampus). Chapter 7 shows learning-dependent gamma oscillations in the orbitofrontal cortex, expressed predominantly by a specific class of cells (‘action-value cells’). Chapter 8, the authors show that neuronal coding of odour-value associations and rhythmic synchronization in OFC is critically dependent on the NMDA receptor.