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Summary: The Brain

The human nervous system, with its billions of nerve cells, is often described as "the most complex system in the known universe." It starts as a tube of cells in the embryo, rapidly developing three distinct parts called the forebrain, midbrain, and hindbrain.

As the forebrain develops, it folds into wrinkles called convolutions. This allows a great surface area to be packed into the limited space of the skull. Human brains have noticeably more convolutions than brains of other species.

The cerebrum is the large, topmost part of the brain. The cerebral cortex is the outer layer of the cerebrum, where most of the cell bodies are packed.

This layer is visible as a dark layer of gray matter when a preserved brain is sliced. Deep folds in the cerebral cortex, called fissures, are found in the same location on each brain.

Fissures can be used to define major areas on the cerebral cortex called lobes. The temporal lobe is at the side of the brain, below the lateral fissure. The parietal lobe is above the lateral fissure.

The frontal lobe is farthest forward in the brain. It is more developed in humans than in other animals. It contains the prefrontal areas, farthest in front, which are involved in complex mental processes such as planning and creativity.

The two hemispheres of the brain are somewhat specialized for different activities. In right-handed people, language usually depends upon areas on the left. Spatial processing usually involves the parietal lobe on the right.

Emotional processing is also lateralized. Sad or avoidant thinking is more common when the right hemisphere is more active.

However, expert neuroscientists feel that the idea of "right brain thinking" and "left brain thinking" has been overdone. Most complex mental activity involves a mix of areas on the two sides.

Brain imaging techniques can be used to show brain structures or functions. An old technique, electroencephalography (the EEG) yields more information now with computer enhancements. PET scans show fluctuations of brain activity in real time as a person thinks or acts.

Another technique, MRI, was originally used to visualize tumors and soft tissue structures of the brain. A variation called functional MRI (fMRI) became the most commonly used brain scanning technique in cognitive neuroscience. It can spot small, brief areas of activity.

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