Neuroscience and Addiction - (part 3)
In recent years, cognitive neuroscience has shed significant light on the problems of addiction and substance abuse. These researches have uncovered a close relationship between drug addictions, behavioral addictions, compulsions and more normal patterns of reward and motivation.
Central to this information are the ideas that drug and behavioral addictions are not problems with the ‘hedonic impact’ of the reinforcing agent (‘liking’ the drug), but they are problems related to ‘wanting’ or ‘craving’ the agent.
A second important discovery is that the mechanism of craving or incentive salience is mediated by neurons in the midbrain that produce dopamine.
The midbrain dopamine tract runs from the Ventral Tegmental Area at the base of the brain; through the Nucleus Accumbens, at the base of the Ventral Striatum; and finally ending at the Orbito-Frontal Cortex, the apparent control center for motivation and wanting in general (Ruden,1997; Schultz, Dayan and Montague, 1997; Robinson and Berridge, 2001; ; Waelti, Dickenson, and Schultz, 2001; Robinson, 2004; Tobler, Fiorillo and Schultz, 2005)
For a long time, it was believed that people got hooked on drugs or other
substances and behaviors because they felt good. However, this doesn’t explain why, even after substances
or behaviors cease to produce the same ‘whack’, people continue
to seek them out.
The ‘feeling good’ interpretation of behavioral addiction violates some of the cardinal principles of behavioral psychology. Every addictive drug, every behavioral addiction, and every learned behavior is subject to habituation. This means that the more exposure you have to something, the less effective it becomes. When a behavior ceases to be rewarding, the behavior becomes less probable. At some point, the stimulus stops evoking the trained response and the response is said to have been extinguished. So.. where is the truth?
Incentive salience connects to neurophysiology through a series of experiments on single dopaminergic neurons and neural implants measuring the response of the neurons to various stimulus conditions. In general, researchers found that the midbrain dopamine system responds in very specific and predictable ways.
Firstly...
it responds powerfully to novel rewards. Whenever
rewards appear in an unexpected context, these neurons respond vigorously.
Secondly...
the brain seeks “the difference that makes a difference”. If a stimulus fully predicts a reward or if it predicts decreasing reward, the neuronal response decreases and often disappears (This is the neural root of habituation.).
Thirdly...
if the stimulus predicts a reward that appears reliably but increases in value relative to other recent rewards, the neurons again increase the intensity of their response (Schultz, Dayan and Montague, 1997; Robinson and Berridge, 2001; Waelti, Dickenson, and Schultz, 2001; Robinson, 2004; Tobler, Fiorillo and Schultz, 2005).
| Part | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
.....Novelty is a crucial part
