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Magnetic Resonance Imaging (MRI): A noninvasive diagnostic technique that uses magnetic fields to detect subtle changes in brain tissue.

Mannitol: A solution which removes water from the brain by accelerating urinary excretion and thus reduces raised intracranial pressure.

Medulla: Part of the hindbrain, the medulla controls automatic body activities. For example, your heart rate, breathing rate and blood pressure would be very hard to control if you had to do it consciously.

Meningitis: Inflammation of the three membranes that envelop the brain and spinal cord, collectively known as the meninges; the meninges include the dura, pia mater, and arachnoid.

Midbrain: The first major division of the brain. Primary activities center around wakefulness and alertness. People with injury here are often drowsy and hard to arouse.

Motor Cortex: The part of the brain around which mental activity is centered.