Key points

■ Behaviour and emotion are associated with the limbic system, which is found at the limbus (border) between the cerebrum and thalamus.

■ The limbic system includes a variety of telencephalic gyri and nuclei, and structures of the thalamus.

■ Lesions in the limbic system in animals can cause changes in behaviour and emotional responses.

■ The ascending reticular activating system (ARAS) of the brainstem determines arousal (consciousness/awareness) levels and regulates sleep. It is stimulated by collateral axons of most sensory fibres travelling to the thalamus.

■ The ARAS functions as a triage system and ranks incoming information in terms of importance.

■ The neurotransmitter hypocretin is important in controlling the sleep-wake cycle. Abnormalities can result in signs of narcolepsy-cataplexy.