  We study collective behavior of Brodmann regions of human cerebral cortex
using functional Magnetic Resonance Imaging (fMRI) and Random Matrix Theory
(RMT). The raw fMRI data is mapped onto the cortex regions corresponding to the
Brodmann areas with the aid of the Talairach coordinates. Principal Component
Analysis (PCA) of the Pearson correlation matrix for 41 different Brodmann
regions is carried out to determine their collective activity in the idle state
and in the active state stimulated by tapping. The collective brain activity is
identified through the statistical analysis of the eigenvectors to the largest
eigenvalues of the Pearson correlation matrix. The leading eigenvectors have a
large participation ratio. This indicates that several Broadmann regions
collectively give rise to the brain activity associated with these
eigenvectors. We apply random matrix theory to interpret the underlying
multivariate data.
