The largest, topmost layer of the brain is the cerebrum. The external layer of the cerebrum is the nerve-rich cerebral cortex which houses physical sensory processing. The term cortex simply means outer layer. While only 5 millimeters thick, this gray matter has 1/3rd of all the nerve cells in the human brain.
The cortex is a highly modular structure, with numerous specialized areas that communicate with each other through a distributed network of long-range connections. Processing requires routing neuronal activity across weakly-connected cortical regions. Signal strength across regions is maintained via synchronicity in spiking activity, which is furthered by coherent oscillations.
Oscillatory activity unleashes network resonance that amplifies feeble synchronous signals and promotes their propagation along weak connections (“communication through resonance”). The emergence of coherent oscillations is a natural consequence of synchronous activity propagation. ~ French neurobiologist Gerald Hahn et al
Astrocytes help maintain neural oscillations, and so regulate neural network connectivity.
Deeper with the brain, in the white matter, resides centers for voluntary motor control, learning, decision-making, cognitive and emotional functions. The nervy bustle about the cerebral cortex belies executive processing within.
The human cerebrum surrounds older evolutionary parts of the brain common to all vertebrates. The limbic, olfactory, and motor systems are networked via fibers to the brain stem and spinal cord.