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Term Definition
parallel processingWhen various cortical fields and nuclei work together simultaneously, each on a small part of a big information-processing job.

Paranoid SchizophreniaA severe form of mental illness typically characterized by delusions of persecution and hallucinations. This condition may be induced by binge use of stimulants.

Parkinson's DiseaseA disease in which dopamine-containing neurons die. It produces severe impairments in movement, cognitive function, and emotions.

PCP(phencyclidine) PCP has an array of effects. Originally developed as an anesthetic, it may act as an hallucinogen, stimulant, or sedative.

peptidesSmall protein-like compounds made of amino acid building blocks.

perceptionThe conscious awareness of sensory inputs, internal states, or memories.

periaqueductal gray matterA set of nuclei deep within the brain stem that are involved with visceral functions. It also plays a role in the development of physical dependence on opiates.

PET scannerThe machine that detects the radioactive chemicals used to measure brain functions.

PharmacodynamicsThe study of the mechanisms of actions of a drug, the relationship between how much drug is in the body and its effects.

PharmacokineticsThe study of how the body absorbs drugs, how they are distributed throughout the body, and how the body gets rid of drugs.

PhencyclidinePCP has an array of effects. Originally developed as an anesthetic, it may act as an hallucinogen, stimulant, or sedative.

physical dependenceChanges that the brain and body undergo as they adapt to the continued presence of high doses of drugs. Because of these changes, the brain and body eventually come to require the presence of the drug to work properly.

placeboAn inactive substance.

plasticityThe capacity of the brain to change its structure and function within certain limits. Plasticity underlies brain functions such as learning and allows the brain to generate normal, healthy responses to long-lasting environmental changes.

positive reinforcementSomething that increases the likelihood that the behavior that elicited it will be repeated. Positive reinforcement is rewarding, and we typically perceive it as pleasure.

positron emission tomography(PET) A technique for measuring brain function in living human subjects by detecting the location and concentration of tiny amounts of radioactive chemicals.

postsynaptic neuronA neuron that receives messages from neurons on the other sides of its synapses.

prefrontal cortexThe part of the cerebral cortex at the very front of the brain. It is involved with higher cognitive and emotional functions including short-term memory, learning, and setting priorities for future actions.

presynaptic neuronA neuron that releases neurotransmitters into synapses to send messages to other neurons.

preventionStopping drug use before it starts, intervening to halt the progression of drug use once it has begun, changing environmental conditions that encourage addictive drug use.

primary reinforcersStimuli, such as food and water, which produce reward directly, with no learning about their significance or other intervening steps required. Most drugs of abuse are primary reinforcers.

projection neuronsNeurons (usually excitatory) that send their axons away from the local vicinity to communicate with other parts of the brain.

proteinsLarge molecules made up of amino acid building blocks.

PsilocybinA natural hallucinogenic drug derived from a mushroom. It acts on the serotonin receptor.

psychedelic drugDrugs that distort perception, thought, and feeling. This term is typically used to refer to drugs with actions like those of LSD.

Special Thanks:
Addiction Studies Program - Wake Forest University School of Medicine
False Messengers: How Addictive Drugs Change the Brain by David Friedman, PhD, and Sue Rusche, Harwood Academic Publishers, Amsterdam, The Netherlands, 1999. [www.addictionstudies.org]