Brain anatomy. Computer artwork of strands of nerve cells (neurons) in front of an exploded view of the brain seen from behind. The two hemispheres of the cerebrum (the main, outer brain layer) have been pulled to either side (orange, lower right and upper left). This has revealed the primitive systems deep within the brain. The limbic system (pink) controls instinct and moods such as fear, rage, pleasure and the sex urge. Towards the rear and base of the brain is the cerebellum (green), which controls functions like balance, posture and muscle co-ordination. Below this (actually linked to the limbic system) is the brainstem.