A brain lesion is a naturally or experimentally caused destruction of the brain. Electroencephalogram (egg): an amplified recording of the waves of electrical activity that sweep across the brai(cid:374)"s surfa(cid:272)e. these (cid:449)a(cid:448)es are (cid:373)easured (cid:271)y ele(cid:272)trodes pla(cid:272)es o(cid:374) the s(cid:272)alp. Pet (positron emission tomography): a visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task. Mri (magnetic resonance imaging): a technique that uses magnetic fields and radio waves to produce computer-generated images of soft tissue. Mri can reveal the brains functioning as well as its structure. Endocrine system: refers to a set of glands that droduce chemical messengers called hormones. Hormones: substances synthesized by the endocrine slands and travel through the bloodstream. Brainstem: the oldest part of the central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions.