A group of regions in the brain that is involved in the expression and control of emotions, mood, instinct, and fear and plays a major role in long-term memory. The limbic system represents the evolutionarily primitive parts of the forebrain and includes the hippocampus, hypothalamus, thalamus, and amygdala. It contains centres for pleasure and pain that play roles in the development of desires and drives and also in learning and emotional memory.