Neurotransmitter: neurochemical emitted between the junction or synapse between neurons causing bioelectrical impulses to travel between neurons and increase synaptic efficiency (connectivity), and as an emergent property, comprises thinking. For cognitive and evolutionary psychologists, the bio is removed from the electrical, and the electrical metaphor is used, making the brain into a computer, neurons into circuitry, and neurotransmitters into the stuff that powers a light bulb, which metaphorically came on for the dim bulb psychologists who came up with the idea.
