• Dopamine

This neurotransmitter feeds the reward pathway in the brain, and is involved in motivation, drive, pleasure and addiction. Abnormally high levels of dopamine are linked to loss of contact with reality, delusions and lack of emotion, while low levels have been associated with addictive behaviour and risk taking.

• Noradrenaline

Chemically related to adrenaline, this neurotransmitter is a stress hormone that co-ordinates the fight-or-flight response. It mediates many of the physical components of emotion, including raised heart rate, and also acts in the brain enhancing alertness, cognition and decision-making behaviour.

• GABA

Gamma amino butyric acid (GABA) is the main inhibitory neurotransmitter in the brain – it decreases nerve transmission, allowing neurons time to recover. Increased GABA activity in the brain relieves anxiety and reduces stress.

• Serotonin

First recognised for its ability to constrict blood vessels, serotonin has become widely known as the "happiness hormone." Chemically known as 5-hydroxytryptamine (5-HT), increasing the available serotonin level in the brain is the main target of the most commonly used antidepressants.

• Beta-endorphin

Endorphins are natural opioids, produced by the body in response to pain, excitement and even exercise. Beta-endorphin binds to the same mu receptors as the pain-relieving drug morphine. These receptors, present on nerves in the brain and spinal cord, modulate the activity of nerves, causing mild sedation, relieving pain and giving a sense of wellbeing.

• Oxytocin

Often described as the "bonding hormone", the "trust hormone", or sometimes even the "love hormone", oxytocin is unique to mammals. Although research is still in its infancy, oxytocin is thought to play an important role in human intimacy, childbirth, sexual arousal, trust and pair bonding.