Diagram of the human brain in profile showing the location of the suprachiasmatic nucleus. An arrow labeled light is shown entering the eye. The labeled retina is shown at the back of the eye connected to the labeled optic nerve. The optical nerve is shown entering the center of the brain, with several labeled areas just above it. The labeled suprachiasmatic nucleus is shown as a small area in front of the labeled hypothalamus, which is shown in front of the larger labeled thalamus. A smaller area labeled lateral geniculate nucleus is shown in the center of the thalamus, with a small area labeled pineal gland at the end of the optic nerve and below the thalamus. An arrow labeled signals to body is shown on the spinal cord leading from the area below the optic nerve and down away from the brain.