Dr. Gerald Hecht

THE BRAIN MECHANISMS OF LEARNING

Midbrain: "reinforcement circuits"

The Nucleus Accumbens (NA) and Ventral Tegmental (VTA) circuit.
Millions of axons project from cell bodies in the VTA to the NA where they release dopamine as a neurotransmitter. The VTA in turn sends axons back to the NA where they release GABA as their neurotransmitter.
The dendrites of the neurons in the VTA have receptors for the following neurotransmitters:
nicotinic ACh
B-endorphin
Anandamide
GABA

Every known type of recreational drug (drugs that are taken deliberately by people for no medical reason) acts biochemically somewhere in the VTA-NA brain circuit:

cocaine & amphetamines = dopamine
alcohol, Valium, Xanax, Rohypnol, etc = GABA
Heroin, morphine, codeine, Dilaudid, Demerol, Vicodin, etc = B-endorphin
Cigarettes, Cigars, chewing tobacco, etc = nicotinic ACh
Marijuana, hashish, etc = Anandamide

The VTA-NA plays a vital role in the psychological phenomenon known as OPERANT LEARNING.

DEFINITIONS:

OPERANT LEARNING– Behavior is a function of its consequences
Positive Reinforcement:
strengthens learning by giving the subject something that increases its behavior (usually something desirable)
Negative Reinforcement:
strengthens learning by removing something painful or aversive (note: also increases behavior)
Positive Punishment:
weakens learning by giving the subject something that decreases its behavior (usually something painful)
Negative Punishment:
weakens learning by taking away something that the subject finds reinforcing… (note: also decreases behavior).

BE PREPARED TO ANSWER QUESTIONS ABOUT THORNDIKE’S DISCRETE TRIALS OPERANT STUDIES AND SKINNER’S FREE RUNNING OPERANT STUDIES (SCHEDULES OF REINFORCEMENT, ETC)

KNOW THE PATTERNS OF RESPONDING THAT ARE TYPICAL OF FIXED RATIO (FR) AND FIXED INTERVAL (FI) SCHEDULES OF REINFORCEMENT

REINFORCEMENT "WORKS" BY INCREASING ACTIVITY IN THE VTA-NA CIRCUIT! THUS RECREATIONAL DRUG USE IS A TYPE OF LEARNING--THE BEHAVIOR THAT IS REINFORCED BY THE DRUG IS THAT OF OBTAINING AND ADMINISTERING THE DRUG!

CLASSICAL (PAVLOVIAN) LEARNING

DEFINITIONS:

A neutral stimulus occurs with a stimulusthat evokes a reflex; eventually, the neutral stimulus comes to evoke a response which is almost identical to the reflex.

Conditioned = learned

Conditioned Stimulus (CS)
Conditioned Response (CR)

Unconditioned = a "hardwired" reflex which does not have to be learned.

Unconditioned Stimulus (US)
Unconditioned Response (UR)

Neutral = not involved in the unlearned reflex at all.

Neutral Stimulus (NS)
Orienting Reflex (OR)

Pavlov's "Classic" research with dogs

US(meat powder) leads to UR(salivation)NS (bell) leads to OR (dog attends to bell)
NS (bell) + US (meat) leads to UR (salivation to meat and bell).
CS (bell) leads to CR (salivation to bell alone).

Secondary Reinforcers (e.g., Money):

evidence of Pavlovian elements in Operant Learning.