After providing all the funding for The Brain from Top to Bottom for over 10 years, the CIHR Institute of Neurosciences, Mental Health and Addiction informed us that because of budget cuts, they were going to be forced to stop sponsoring us as of March 31st, 2013.

We have approached a number of organizations, all of which have recognized the value of our work. But we have not managed to find the funding we need. We must therefore ask our readers for donations so that we can continue updating and adding new content to The Brain from Top to Bottom web site and blog.

Please, rest assured that we are doing our utmost to continue our mission of providing the general public with the best possible information about the brain and neuroscience in the original spirit of the Internet: the desire to share information free of charge and with no adverstising.

Whether your support is moral, financial, or both, thank you from the bottom of our hearts!

Bruno Dubuc, Patrick Robert, Denis Paquet, and Al Daigen

Monday, 30 April 2012
Theories on Drug Addiction


The human brain contains circuits that provide us with pleasure to reinforce behaviours that are helpful to our survival. The brain thus naturally favours those behaviours that lead us to seek euphoria. The abusive consumption of a drug can result in dependency on it. The various phenomena associated with drug dependency—also commonly referred to as “drug addiction”—are fairly well known: initial pleasure, then tolerance, withdrawal, and so on. Experts have identified several signs of drug dependency. If someone displays several of them, that is a good indication that they have become dependent on the drug in question. These signs include:

-a persistent desire for the drug and an inability to stop taking it
-the development of a tolerance for the drug that forces them to keep taking larger doses to achieve the same effects
-the onset of withdrawal symptoms when they cannot obtain the drug
-spending a great deal of their time obtaining the drug, consuming it, and recovering from its effects
-an inability to stop or control their consumption of the drug, even when it goes against their own values
-continuing to take the drug, even when they recognize the major physical, psychological, and social problems caused by this behaviour

But these phenomena are so complex that it is hard to construct satisfactory models for them. Hence, many theories have been developed to try to explain drug dependency/addiction, and these theories are still being debated today.

One of these theories is based on the traditional hedonist principle that people seek pleasure and avoid pain. For other theorists, the main cause of drug addiction is the desire to alleviate the suffering that addicts experience when their drug is withdrawn. Still another theory holds that drug-dependent people suffer from a dysfunction of the systems of the frontal cortex that normally regulate decision-making and impose inhibitory controls on behaviour. This dysfunction would result in altered judgment and impulsiveness. One last hypothesis focuses on the idea that individuals’ attitudes toward drugs depend fundamentally on whether the baseline activity of the dopaminergic neurons in their brains is above or below a certain level.

The Intermediate (green) link below takes you to an explanation of one of these theories, the opponent-process theory, complete with diagrams.

The Advanced (red) link takes you to a discussion of some recent neurochemical data that tend to support the effects described in the opponent-process model.

i_link Addiction and the Opponent Process Theory
a_link Addiction and the brain antireward system

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