‘chemical’ produced by the neuron, and the receptor site may be too responsive or not responsive enough. The chemicals that inactivate the neurotransmitters may be too abundant or inadequate. The effects of either alteration of chemicals is what produces mental disorders. The theory is the result of studies done primarily in animals. Chemicals known to affect the neurotransmitters (either by increasing or decreasing the amount released by the sending neuron or by increasing or blocking the uptake