Brainwaves. Abstract illustration of a spiked waveform and the human brain, depicting a thought pattern or some mental state. It may also repre sent headache or the pain of migraine. Electrical impulses are produced by the activity of the brain when measured on an EEG (electroencephalogram). Such wave patterns alter when awake, asleep, or undergoing thought processes. At above centre, the folded cerebrum of the brain can be seen: this largest area of the brain is concerned with con scious thought, sensation and movement. Below centre, the brainstem (attaches the spinal cord) and cerebellum (at right) are involved in uncons cious body functions of breathing and balance.