Until recently, what doctors and scientists knew about brain function came from observing what stopped working when the brain was injured. Studying head-trauma victims, they attributed different functions to various structures of the brain. They found, for instance, that an injury to the temporal lobe of the brain often compromised a patient's language skills.

New technologies allow scientists to look deep within the human brain and observe what's happening there. For example, Functional Magnetic Resonance Imaging (fMRI) scanners detect the levels of oxygen in blood flowing through an area of the brain. Because blood oxygen levels and brain activity are positively correlated, scientists can tell whether a given part of the brain is functioning during certain tasks: Higher oxygenation means increased neural activity.

Normal brain activity relies on communication between networks of specialized nerve cells, called neurons, and other types of cells in the body. Neurons transmit signals via electrical pulses to control the release of chemicals. These chemicals, called neurotransmitters, are then passed to other neurons or directly to the cells of a target tissue, like a muscle. Neurotransmitters have either an excitatory or an inhibitory effect on neighboring cells. This means that they can either increase or decrease the likelihood that a target cell will be stimulated to forward its own electrochemical signals.

One's ability to identify with and understand another person's situation, feelings, or motives is called empathy. How humans generate empathy remains a subject of debate in cognitive science. Some scientists believe they may have finally discovered its root in specific kinds of nerve cells—mirror neurons. First identified in monkeys in the 1990s, mirror neurons are also known as "monkey-see, monkey-do" cells.

Scientists noted that mirror neurons were active when a monkey performed an action, like reaching out to grab a peanut, as well as when the monkey observed the same action being performed by another monkey. Thus, the neuron activity in the observer monkey mirrored that of the monkey performing the action, just as if the observer monkey had performed the action itself. Interestingly, there is evidence that a similar "observation-action" matching system exists in humans.

Drawing on this connection, researchers have implicated the mirror neuron system in a broad range of human conditions, including certain cognitive disorders. For example, some dysfunction or deficiency in the mirror neuron system may underlie autism, which is characterized by an impaired ability to communicate and relate to others. Understanding the neural basis of autism may lead to early diagnosis and potential therapies.

To learn more about the structures and functions of the brain, check out Growing Up with Epilepsy: Brain Anatomy and Development.

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