July 20, 2005
Rats Show Cocaine Reduces Ability To Modify Learned Behavior

Addictive drugs are bad for the brain.

Researchers working with rats have zeroed in on the brain circuitry mechanism whose disruption contributes to the impulsive behavior seen in users of cocaine as well as other psychostimulant drugs. The same circuitry has been implicated in such disorders as schizophrenia, depression, and post-traumatic stress disorder, wrote the researchers.

Yukiori Goto and Anthony A. Grace of the University of Pittsburgh described their findings in the July 21, 2005, issue of Neuron. In their studies, they sought to understand the effects of cocaine sensitization on the connections between two higher brain regions--the prefrontal cortex and the hippocampus--and the nucleus accumbens, which is the region in the limbic system involved in processing reward behavior. The prefrontal cortex is involved in processing information, and the hippocampus is involved in learning and memory.

The connections to the nucleus accumbens seem to be bidirectional, said the researchers, and the interactions with the prefrontal cortex and hippocampus could affect the "plasticity" of connections in the neurons of the nucleus accumbens. This means that disruptions to the normal connections could affect behavior.

The researchers' electrophysiological studies of the effects of cocaine on this circuitry demonstrated that the drug did disrupt this normal plasticity. They found that the cocaine induced abnormal enhancement of neuronal connections--a phenomenon called long-term potentiation (LTP).

The researchers also performed behavioral studies on the cocaine-sensitized rats, to explore the behavioral effects of this disruption. In these studies, they placed the rats in a plus-shaped maze. The rats were taught that in response to a visual cue they should turn left or right toward one arm or the other of the maze to obtain a piece of cereal.

Goto and Grace found that, while the cocaine-sensitized rats learned the correct response strategy faster than normal rats, they were significantly less able to change strategies when they were required to ignore the cue and always make a left or right turn to receive the reward.

"Thus, although abnormally induced LTP by psychostimulants at limbic inputs might not interfere with learning a response strategy, it may reduce the capacity of these animals to consider alternate response strategies," concluded Goto and Grace. "In this way, the disruption of synaptic plasticity by cocaine sensitization may contribute to the affective- and context-inappropriate impulsive behaviors that are characteristic of drug addiction."

A drug that increases impulsive behavior in its users creates problems (e.g. crime, poorer relations with friends, neighbors, familiies) for the rest of us. Cocaine addicts have a harder time modifying some behavior or lesson already learned. One can imagine how that would cause them to get stuck in ruts of repetitive behavior that is destructive to themselves and to other people..

Cocaine addicts are more oriented toward pleasure.

“It may explain why cocaine addicts are oriented towards pleasure rather than other goals, and have an impaired ability to make decisions. It could be why addicts go back to taking more of the drug and ex-addicts often become addicted again faster than those who have never taken it,” says Grace

Drugs that reduce cognitive competence increase the costs that users impose on the rest of us while at the same time the drugs make the users less productive. Users simultaneously increase the costs they impose while giving less in return. We need treatments that cure addictions. We also need better drugs that make us more adaptive, not less.

Share |      Randall Parker, 2005 July 20 04:28 PM  Brain Addiction

JoeT said at July 21, 2005 3:10 AM:

The article seems to be painting this more as a commonality of addictive drugs than only of cocaine. If that were so, the fact that most westerners are addicted to caffeine, nicotine, or a combination of both might be enough to get me to lay down the coffee mug. Anyone aware of any other studies which might be relevant to alternations of neuronal plasticity in addiction to either of these substances? Or, perhaps someone with access to the journal article might be able to comment on whether the researchers felt this effect to only be specific to cocaine or other opiate derivatives.

RK said at July 21, 2005 8:31 AM:

Goto and Grace found that, while the cocaine-sensitized rats learned the correct response strategy faster than normal rats...

This meshs with what we know about the effect of stimulents such as Methylphenidate and dextroamphetamine on learning. The kids take em to study. (and for other reasons!)
Other studies have shown that caffeine aids in learning as well.
But does caffeine also create a bit of a one track mind? Let's have some more studies!

side said at July 22, 2005 1:16 AM:


'Some kinds of brain damage can make better stock investors'

Braddock said at July 22, 2005 5:41 AM:

The brain actually makes all the drugs that most people need. The problem is balancing the brain's production of chemicals with the person's activity/needs of the moment. It becomes much easier to force the issue with exogenous chemicals than to learn to coax the brain to make the appropriate chemical balance for the moment.

When you come to realize that foods themselves function as psychoactive substances you can accept that we humans are always taking "drugs" and always will. The goal should be to assist the brain's ability to adapt to changing circumstances, not merely to support a concretized routine at the expense of adaptibility. Stimulants support routine functions, and support some forms of learning but not necessarily well retained or useful learning. Just enough to pass the test this time.

Jim said at July 22, 2005 7:54 AM:

RP - I like your post here. I think it's helpful for teaching kids the real reasons not to take drugs - to show them real scientific evidence of the damage done by drugs, cause kids have fantastic bullshit detectors. Thanks!!

Randall Parker said at July 22, 2005 10:17 AM:



One of my goals in writing FuturePundit is to explain how we are sometimes quite maladapted to the things that technology allows us to produce and use. So this is why I write posts on how various addictive drugs harm the brain and cause self destruction behaviors. I want to get people to understand that we can't handle some things we introduce into our environments.

With addictive drugs I think the costs are huge and tragic. If you go into my Brain Addiction archives you will find other posts that describe "the needle and the damage done" (to quote Neil Young).

dissociative freak said at August 7, 2005 3:24 PM:

I think that the drug I have been taking (a dissociative drug) has made me more pleasure-oriented, and perhaps worsened my attention deficit issues (though this may be due to rebound effects rather than permanent or semi-permanent changes in the brain). Dissociatives are generally not considered to be nearly as addictive as cocaine, speed, or heroin, but for some people (unfortunately myself included) they can be quite compelling, and do have known negative effects (such as cognitive impairment with heavy, frequent use).

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