<P> Most of the enlargement of the primate brain comes from a massive expansion of the cerebral cortex, especially the prefrontal cortex and the parts of the cortex involved in vision . The visual processing network of primates includes at least 30 distinguishable brain areas, with a complex web of interconnections . It has been estimated that visual processing areas occupy more than half of the total surface of the primate neocortex . The prefrontal cortex carries out functions that include planning, working memory, motivation, attention, and executive control . It takes up a much larger proportion of the brain for primates than for other species, and an especially large fraction of the human brain . </P> <P> The brain develops in an intricately orchestrated sequence of stages . It changes in shape from a simple swelling at the front of the nerve cord in the earliest embryonic stages, to a complex array of areas and connections . Neurons are created in special zones that contain stem cells, and then migrate through the tissue to reach their ultimate locations . Once neurons have positioned themselves, their axons sprout and navigate through the brain, branching and extending as they go, until the tips reach their targets and form synaptic connections . In a number of parts of the nervous system, neurons and synapses are produced in excessive numbers during the early stages, and then the unneeded ones are pruned away . </P> <P> For vertebrates, the early stages of neural development are similar across all species . As the embryo transforms from a round blob of cells into a wormlike structure, a narrow strip of ectoderm running along the midline of the back is induced to become the neural plate, the precursor of the nervous system . The neural plate folds inward to form the neural groove, and then the lips that line the groove merge to enclose the neural tube, a hollow cord of cells with a fluid - filled ventricle at the center . At the front end, the ventricles and cord swell to form three vesicles that are the precursors of the forebrain, midbrain, and hindbrain . At the next stage, the forebrain splits into two vesicles called the telencephalon (which will contain the cerebral cortex, basal ganglia, and related structures) and the diencephalon (which will contain the thalamus and hypothalamus). At about the same time, the hindbrain splits into the metencephalon (which will contain the cerebellum and pons) and the myelencephalon (which will contain the medulla oblongata). Each of these areas contains proliferative zones where neurons and glial cells are generated; the resulting cells then migrate, sometimes for long distances, to their final positions . </P> <P> Once a neuron is in place, it extends dendrites and an axon into the area around it . Axons, because they commonly extend a great distance from the cell body and need to reach specific targets, grow in a particularly complex way . The tip of a growing axon consists of a blob of protoplasm called a growth cone, studded with chemical receptors . These receptors sense the local environment, causing the growth cone to be attracted or repelled by various cellular elements, and thus to be pulled in a particular direction at each point along its path . The result of this pathfinding process is that the growth cone navigates through the brain until it reaches its destination area, where other chemical cues cause it to begin generating synapses . Considering the entire brain, thousands of genes create products that influence axonal pathfinding . </P>

What is the highest function of the brain