The F1 is an organ with distinct regions that mediate specific cerebral functions; regions are linked together into cerebral systems that mediate complex mental tasks. Even though the cellular constituents of brain regions can be similar (large neurons, interneurons, glia, and neurophil), their local and long tract connections are distinctive, as are aspects of their anatomy and neurochemistry. Almost all regions are structurally and functionally plastic well into maturity. The cerebral cortex has distinct regions (frontal, temporal, parietal, and occipital); subcortical structures (basal ganglia, thalamus, hypothalamus) interact with the cortex, often topographically. The cortex, both limbic and neocortex, is organized into layers that subserve its inputs, local circuits, and outputs. Even without a full understanding of how the human brain functions, systems of regional classification have sprung up to facilitate communication. One of the best known is the Brodmann’s Area classification, a system based on cellular morphology. Brodmann divided the cerebral regions into 46 surface areas. The regional demarcations are still used today because they describe regions that may be a "unit" size for behavioral function and are an easy descriptive tool. Both anatomic and functional features of the human brain are often mapped onto Brodmann’s areas.