Non-identical twins. Two individuals that develop in one uterus from separately fertilised eggs. Also called fraternal twins.

Short for deoxyribonucleic acid. DNA is a macromolecule made up of individual units called nucleotides, and is found in all living cells and some viruses. The DNA molecule exists as a complex of two chains in an intertwined double helix. It is the carrier of genetic information that is passed on from generation to generation by replication of the DNA molecule.

One of the brain’s neurotransmitters (chemical messengers).

The idea that mental events and brain events are two aspects of the same underlying reality.

The situation where a lesion at site A produces a disturbance in function X but not Y, and a lesion at site B produces a disturbance in function Y but not X.

The contribution of internal factors to motivation.

Diagnostic and Statistical Manual (of mental disorder). An American-based reference text; the ‘Bible’ of classification of psychological disorders. DSM I was first published in 1952 and has been updated several times since then. (The number, i.e. I, II, etc., denotes the edition.)

The idea that brain events and mind events are two distinct categories of existence. According to this, the mind can exist even in the absence of a physical brain.

Negative mood, e.g. depression; the opposite of euphoria. (Adjective: dysphoric.)