1. The act of rendering active.

2. An increase in the energy content of an atom or molecule, through the raising of temperature, absorption of light photons, etc., which renders that atom or molecule more reactive.

3. Techniques of stimulating the brain by light, sound, electricity, or chemical agents, in order to elicit abnormal activity in the electroencephalogram.

4. Stimulation of peripheral nerve fibers to the point that action potentials are intiated.

5. Stimulation of cell division in an ovum by fertilization or by artificial means. See: cross-section.

6. The act of making radioactive.

amino acid activation

EEG activation

feedback activation

feed-forward activation

gene activation