Loss, but not absence, of control – How choice and addiction are related

In a recent post the notion that “loss of control” is an addiction myth was raised by our contributing author, Christopher Russell, a thoughtful graduate student studying substance abuse in the U.K. Though I obviously personally believe in control- and choice-relevant neurological mechanisms playing a part in addiction, this conversation is a common one both within and outside of the drug abuse field. Therefore, I welcome the discussion onto our pages. I’d like to start out by reviewing some of the more abstract differences between my view and the one expressed by Christopher and follow those with some evidence to support my view and refute the evidence brought forth by him.

Addiction conceptualization – Philosophical and logical differences and misinterpretations

One of the first issues I take with the argument against control as a major factor in drug addiction is the interpretation of the phrase “loss of control” as meaning absence, rather than a reduction, in control over addiction and addictive behavior. Clearly though, one of the definitions of loss is a “decrease in amount, magnitude, or degree” (from Merriam-Webster.com) and not the destruction of something. Science is an exercise in probabilities so when scientists say “loss”, they mean a decrease and not a complete absence in the same way that findings showing that smoking cigarettes causes cancer do not mean that if an individual smokes cigarettes they will inevitably develop cancerous tumors. Similarly, the word “can’t” colloquially means having a low probability of success and not the complete inability to succeed. Intervention that improve the probability of quitting smoking (like bupropion or quitlines for smoking) success are therefore said to cause improvements in the capacity for quitting.

Next, Christopher wants scientists to identify the source of “will” in the brain but I suggest that “will” itself is simply a term he has given a behavioral outcome – the ability to make a choice that falls in line with expectations. In actuality, “will” is more commonly used as a reference to motivation, which while measurable, isn’t really the aspect of addiction involved in cognitive control. Instead, what we’re talking about is “capacity” to make a choice. The issue is a significant, not semantic one, since the argument most neuroscientists make about drug abuse is that addicts suffer a reduced capacity to make appropriate behavioral choices, especially as they pertain to engaging in the addictive behavior of interest. If someone is attempting to get into a car but repeatedly fails, we say they can’t get in the car (capacity), not that they don’t want to (will). Saying that they simply “don’t” get in the car doesn’t get at either capacity or will but instead is simply descriptive. I don’t believe that science is, or should be, merely descriptive but instead that it allows us to form conclusions based on available information.

That there is a segment of individuals who develop compulsive behavioral patterns tied to alcohol and drug use and who attempt to stop but fail is, to my mind, evidence that those individuals have a difficulty (capacity) in stopping their drug use. Their motivation (will) to quit is an aspect that has been shown to be associated with their probability of success but the two are by no means synonymous. It is important to note, and understand, that the attribution for the performance should not fall squarely on the shoulders of the individuals. We humans are so prone to making that mistake that it has a name, “The fundamental attribution error,” and indeed, individuals who show compulsive, addictive, behavior do so because of neuropharmacological, environmental, and social reasons in addition to the complex interactions between them all. But no one is disputing that and in fact, the article used by Christopher to point out the notion of a “tipping point” in addiction directly points out that fact in the next paragraph (Page 4), which he chose not to reference or acknowledge.

“Of course, addiction is not that simple. Addiction is not just a brain disease. It is a brain disease for which the social contexts in which it has both developed and is expressed are critically important… The implications are obvious. If we understand addiction as a prototypical psychobiological illness, with critical biological, behavioral, and social-context components, our treatment strategies must include biological, behavioral, and social-context elements.” (Lashner, 1997)

Lastly, Christopher’s philosophical musings are interesting, but they seem to stray away from trying to find an explanation for behavior and instead simply deconstruct evidence. In a personal communication I explained that while most addiction researchers understand that addiction, like most other mental health disorders is composed of a continuum of control ranging from absolute control over behavior to no control whatsoever (with most people fitting somewhere in the middle and few if any at the extreme ends), categorization is a necessary evil of clinical treatment. The same is true for every quantitative measure from height (Dwarfism is sometimes defined as adults who are shorter than 4’10”) to weight (BMI greater than 30 kg/m²). I think it’s equally as tough to argue that someone with a BMI of 29.5 is distinctly different from an individual with a BMI of 30 as it is to argue that there is no utility in the classification. Well, the same applies for drug addiction, although some people categorically object to classification and believe it has no utility or justification.

Now for the evidence – “Choice” and “control” are not the same as “will”

Some people quit, even without help – Christopher and a number of the people he cites in support (Peele, Alexander), suggest that because some people do stop using that it can’t be said that there is a problem with any individuals’ capacity to stop. The problem with that argument is that it supposes that everyone is the same, a fact that is simply false. As an example I would like to suggest that we compare cognitive control with physical control and use Huntington’s Disease (HD or Huntington’s Chorea) as an example.

HD patients suffer mental dementia but the physical symptoms of the disease, an inability to control their physical movement resulting in flailing limbs often referred to as the Huntington Dance, are almost always the first noticeable symptoms. Nevertheless, HD sufferers experience a number of debilitating symptoms that originate in brain dysfunction (specifically destruction of striatum neurons, the substantia nigra, and hippocampus) and that alter their ability (capacity) to control their movements and affect their memory and executive function leading to problems in planning and higher order thought processes. So, while it is true that most people can control their arm movements, here is an example of individuals who progressively become worse and worse at doing so due to a neurophramacological disorder. There is currently no cure for HD but some medications that help treat it no doubt restore some of the capacity of these patients to control their movements. If a cure is found it would be difficult to say, as Christopher suggests of addiction, that the cure does not affect the capacity of HD patients to control what they once could not. I chose HD for its physiological set of symptoms but a similar example could easily be constructed for schizophrenia and a number of other mental health disorders (including ADHD and drug addiction). Importantly, cognitive control is a function of brain activity, activity that can become compromised as the set of experiment I will discuss next show.

An experiment conducted at UCLA (1) has shown that cocaine administrations reduced animals’ ability to change their behavior when environmental conditions called for it. Even more meaningful was the finding that once animals are exposed to daily doses of drugs, the way their learning systems function is altered even when the drugs themselves are no longer on board and even when the learning has nothing to do with drugs per se.

In the experiment, conducted by Dr. David Jentsch and colleagues, monkeys were given either a single dose (less than the equivalent of a tenth of a gram for a 150lb human) or repeated doses (1/8 to 1/4 of a gram equivalent once daily for 14 days) of cocaine. The task involved learning an initial association between the location of food in one of three boxes and then learning that the location of the food has changed. We call this task reversal learning since animals have to unlearn an established relationship to learn a new one.

Obviously, the animals want the food, and so the appropriate response once the location is changed is to stop picking the old location and move on to the new one that now holds the coveted food. This sort of thing happens all the time in life and indeed, during addiction it seems that people have trouble adjusting their behavior when taking drugs is no longer rewarding and is, in fact, even troublesome (as in leading to jail, family breakups, etc.).

In the experiment, animals exposed to cocaine had trouble (when compared to control animals that got an injection of saline water) learning to reverse their selection when tested 20 minutes after getting the drug, which is not surprising but still an example of how drug administration can causally affect an individual’s ability to make appropriate choices. As pointed above, the most interesting finding had to do with the animals that got a dose of cocaine every day for 14 days. Even after a full week of being off the drug, these animals showed an interesting effect that persisted for a month – while their ability to learn that initial food-box association, they had significant trouble changing their selection once the conditions changed. Remember, this effect was present with no cocaine in their system and with learning conditions that had nothing whatsoever to do with cocaine.

If that’s not direct evidence that having drugs in your system can alter the way your brain makes choices, I don’t know what is.

Another study conducted by Calu and colleagues with rats found similar (or even more pronounced) reversal learning problems after training the animals to take cocaine for themselves, clarifying that it is the taking of cocaine and not the method that causes the impairments.

Another entire set of studies has shown that stimuli (also known as cues or triggers) that have become associated with drugs can bring back long-forgotten drug-seeking behavior once they are reintroduced. This was shown in that Calu paper I mentioned above and in so many other articles that it would be wasteful to go through all the evidence here. Importantly, this evidence shows that drug associated cues direct behavior towards drug seeking in a way that biases behavior regardless of any underlying will. My own research has shown that animals who respond greatly to drugs (nicotine in our case) likely learn to integrate more of these triggers than animals who show a reduced response, indicating once again that these animals bias  their behavioral selection towards drug-seeking more than usual. While we have more studies to conduct, we believe that genetic differences relevant to dopamine and possibly other neurotransmitters important for learning (like Glutamate) are responsible for this effect.

While we can’t do these kinds of experiments with people (research approval committee’s just won’t let you give drugs to people who haven’t used them before), there is quite a bit of evidence showing an association between trouble in reversal learning and chronic drug use in humans (see citation 3 for example) as well as research showing very different brain activity among addicted individuals to drug-associated versus non-drug cues (like seeing a crack pipe versus a building). All this evidence suggests that drug users are different in the way they learn generally, and more specifically about drugs, than individuals not addicted to drugs. When it comes to genetics, we know quite a bit about the  association between substance abuse and specific genes, especially when it comes to dopamine function. As expected, genetic variation in dopamine receptor subtypes important in learning about rewards (D4 and D2) has been revealed to exist between addicts and non addicts. Without getting into the techniques and analysis methods involved in these genetic studies, their sheer number and the relationship between substance abuse and other impulse disorders points to a direct relationship between drug use disorders (and possibly other addictive disorders) and a reduced capacity to exert behavioral control. Less capacity for control is what researchers have found sets addict apart from non-addicts.

Summary, conclusions, and final thoughts

The toyota Prius is slow but efficientIn closing, there are undoubtedly imperfections about the ways we diagnose addiction (drug addiction and others). It would probably be nice if we could figure out a way to incorporate what we know about the continuous nature of the disorder with the need for clinical delineation of who requires addiction treatment and who doesn’t. Addiction researchers are far from the only ones who wonder about this question though (the same issues are relevant for schizophrenia, depression, and nearly every mental health disorder) and I am certain that better and better solutions will emerge.

However, the discussion of stigma in this context needs to allow us to discuss the reality of addiction without having to resort to blaming and counter-blaming. If I describe the Toyota Prius as being slow but incredibly efficient I am no more stigmatizing than if I describe a Ferrari as being incredibly fact but wasteful in terms of fuel. The same applies, or should apply, to health and mental health diagnoses – Just because an individual is less able to exert cognitive control over impulses should not by definition call into question their standing as a human being. We are complex machines and by improving our understanding of the nuts and bolts that make us function we can only, in my opinion, improve our ability to make the best use of our capabilities while understanding our relative strengths and weaknesses. Any other way of looking at it seems to me to be either wishful (I can do anything if I want it badly enough) or defeatist (I will never be anything because I’m not good at X) and neither seem like good options to me.

Citations:

1) Jentsch, Olausson, De La Garza, and Tylor (2002): Impairments of Reversal Learning and Response Perseveration after Repeated, Intermittent Cocaine Administrations to Monkeys. Neuropsychopharmacology, Volume 26, Issue 2, Pages 183-190

2) Calu et al (2007) Withdrawal from cocaine self-administration produces long-lasting deficits in orbitofrontal-dependent reversal learning in rats. Learning & Memory, 14, 325-328.

3) Some evidence in humans from Trevor Robbins’ group: Reversal deficits in current chronic cocaine users.

A new candidate for ADHD medication: Amantadine and the rise of non-stimulants

It is well known that ADHD diagnoses and substance abuse problems are closely associated. It is estimated that substance abuse problems including dependence are up to twice as common among individuals with ADHD, which is not surprising given the impulsivity factor involved in ADHD. The problem is that until recently, most medications for ADHD have belonged to the stimulant category and as many, including us, have written before it is probably not the best idea ever to give drugs that have a relatively large abuse probability to people who are relatively likely to develop substance abuse problems. Right?

We’ve already written about atomoxetine and bupropion, two drugs with relatively low abuse potential (since patients don’t actually feel “high” from them) that are being successfully used in treating ADHD. But there is little doubt that the type of effect seen among patients who are using stimulants (like adderall, ritalin, etc.) isn’t being observed among patients taking non-stimulant medications. All of this means that patients on non-stimulants are getting less bang but with less risk. A dopamine agonist by the name of amantadine might change all of that according to a recent study.

Amantadine versus stimulants for ADHD treatment

Fourty children between the ages of 6 and 14 were enrolled in the study conducted in a psychiatric hospital in Iran. The kids were randomized into two groups a methylphenidate (ritalin) and amantadine group. Over a six week period the kids were assessed four times – at intake and then every two weeks -using an instrument that parents and teachers (who didn’t know what medication the kids were getting) would use to rate the child’s behavior on the 18 ADHD symptoms listed in the DSM-IV.

Amantadine may soon offer a new non-stimulant medication option for ADHD treatmentThe final findings were very encouraging (see picture): The kids in both conditions improved greatly over the 6 weeks of the study and no difference was found between the two medications. the children in the amantadine condition actually suffered less side effects and significantly so when looking at side effects common to stimulant medication such as decrease in appetite and restlessness. While more studies are obviously needed, this randomized trial shows that amantadine is not only safe, but it may be safer than at least some stimulant medications while also providing the same effect on ADHD symptoms. Given that approximately 30% of patients don’t respond well to stimulants and that some families are afraid of giving stimulant medications to their children, at least partially because of the risk of substance abuse issues, non-stimulant medications can be an attractive alternative, and it seems like amantadine can deliver.

Final thoughts from Dr. Jaffe on ADHD medications and amantadine

One of the main reservations I have about the notion of using this medication for ADHD is that NMDA receptors are very important in learning, so it may be that we’re helping to resolve attention problems but making it more difficult to actually create memories that are crucial for learning. More research is necessary to see if these decreases in impulsivity are accompannied by improvements, and not reductions, in learning ability.

So, if you’re considering medicating a child who has been diagnosed with ADHD, I strongly support the notion given the difference that medication has made in my own life. However, I urge you to be educated and to consider non-stimulant options, especially as more are researched and as that treatment option becomes more available, less costly, and less likely to lead to abuse of the drug. With prescription drug abuse one of the fastest growing problems in the U.S., being careful is just sound advice.

Citation:

Mohammad-Reza Mohammadi, Mohammad-Reza Kazemi, Ebtehal Zia, Shams-Ali Rezazadeh, Mina Tabrizi, Shahin Akhondzadeh (2010) Amantadine versus methylphenidate in children and adolescents with attention deficit/hyperactivity disorder: a randomized, double-blind trial. Human Psychopharmacology.

Some parkinson work showing effect of amantadine: http://www.springerlink.com/content/76r5wxux8wn52rq5/fulltext.pdf

Is marijuana addictive? You can bet your heroin on that!

marijuana“Is marijuana addictive?” seems to be the ultimate question for many people. In fact, when discussing addiction, it is rare that the addiction potential for marijuana doesn’t come up.

Some basic points about marijuana:

The active ingredient in marijuana, THC, binds to cannabinoid receptors in the brain (CB1 and CB2). Since it is a partial agonist, it activates these receptors, though not to their full capacity. The fact that cannabinoid receptors modulate mood, sleep, and appetite is why you get the munchies and feel content and why many people use it to help with sleep.

But how is marijuana addictive? What’s the link to heroin?

What most people don’t know is that there is quite a bit of interaction between the cannabinoid receptor system (especially CB1 receptors) and the opioid receptor system in the brain. In fact, research has shown that without the activation of the µ opioid receptor, THC is no longer rewarding.

If the fact that marijuana activates the same receptor system as opiates (like heroin, morphine, oxycontin, etc.) surprises you, you should read on.

The opioid system in turn activates the dopamine reward pathway I’ve discussed in numerous other posts (look here for a start). This is the mechanisms that is assumed to underlie the rewarding, and many of the addictive, properties of essentially all drugs of abuse.

But we’re not done!

Without the activation of the CB1 receptors, it seems that opiates, alcohol, nicotine, and perhaps stimulants (like methamphetamine) lose their rewarding properties. This would mean that drug reward depends much more heavily on the cannabinoid receptor system than had been previously thought. Since this is the main target for THC, it stands to reason that the same would go for marijuana.

So what?! Why is marijuana addictive?

Since there’s a close connection between the targets of THC and the addictive properties of many other drugs, it seems to me that arguing against an addictive potential for marijuana is silly.

Of course, some will read this as my saying that marijuana is always addictive and very dangerous. They would be wrong. My point is that marijuana can not be considered as having no potential for addiction.

As I’ve pointed out many times before, the proportion of drug users that become addicted, or dependent, on drugs is relatively small (10%-15%). This is true for almost all drugs – What I’m saying is that it is likely also true for marijuana (here is a discussion of physical versus psychological addiction and their bogus distinction).

Citation:

Ghozland, Matthes, Simonin, Filliol, L. Kieffer, and Maldonado (2002). Motivational Effects of Cannabinoids Are Mediated by μ-Opioid and κ-Opioid Receptors. Journal of Neuroscience, 22, 1146-1154.

Physical addiction or psychological addiction – Is there a real difference?

This is another one of the basic questions I get regarding addiction.

It seems that people think about physical addiction and psychological addiction as somehow separate processes. I think this distinction makes no sense. Even if people really meant what they were saying, the brain is undoubtedly part of the body, and therefore, psychological addictions are also physical.

The “Physical Addiction” Vs. “Psychological Addiction” truth

blackboardWhat people are really referring to when they make this comparison is the distinction between physical withdrawal symptoms and the addictive process in the brain. There’s no doubt that some substances, like alcohol, opiates, and the likes, leave long term users with horrible withdrawal symptoms that are terrible to watch, and even worse to go through. In fact, early addiction theories asserted that it was this horrible withdrawal syndrome that made people go back to drugs. This was called the Tolerance-withdrawal addiction theory.

The Tolerance-withdrawal addiction theory fell apart when addictions to substances that didn’t display such withdrawal effects became obvious (like cocaine addiction), and when getting people through the difficult withdrawal proved insufficient to cure their addiction (naltrexone was thought to be the magic cure once upon a time).

In one of my previous posts about marijuana addiction, a reader suggested that since marijuana does not produce horrible withdrawal symptoms, it can not be physically addictive. While withdrawal from marijuana, cocaine, methamphetamine, nicotine, and numerous other drugs does not result in the stereotypical “opiate-withdrawal-flu-like-syndrome,” there is no doubt that real withdrawal from these substances exists for long term users and it sucks: Fatigue, depression, anxiety, sleep disturbances, and trouble eating are only some of the symptoms that tend to show up.

Withdrawal – The real physical addiction

Withdrawal symptoms occur because the body is attempting to counteract the stoppage of drug ingestion. Just like tolerance builds as the body adjusts to chronic drug use, withdrawal occurs as the body reacts to its cessation.

As crystal meth increases the amount of dopamine present in the brain, the body reacts by producing less dopamine and getting rid of dopamine receptors. When a user stops putting meth in their body, the low production of dopamine must increase and additional receptors must be inserted. Like tolerance, the process of withdrawal, even past the initial, obvious, symptoms, is a long and complicated one. For crystal meth addicts, the initially low levels of dopamine result in what is known as anhedonia, or an almost complete lack of pleasure in anything. There’s no mystery as to why: Dopamine is one of the major “pleasure” neurotransmitters. No dopamine, no pleasure.

The process of addiction in the brain

So, if we’re going to try to dissect which drugs cause what effects on the body, it’s important that we understand the underlying causes for those effects and that we use the proper language. Withdrawal, tolerance, and addiction are different, though obviously related topics. Their interplay is key for understanding the addiction process, but their more subtle points can often be lost on those observing addicts unless they are well trained.

As I’d mentioned in earlier posts, our current best notions about addiction are that the process involves some obvious physical and psychological processes and some much more subtle effects on learning that are still being studied. A study I’m currently conducting is meant to test whether drugs interfere with some of the most basic learning processes that are meant to limit the amount of control that rewards have over behavior. Such fine distinctions are no doubt the result of the ways in which drugs alter the neurochemical reactions that take place in our brain. Such basic changes can not possibly be seen as any less important than physical withdrawal symptoms.

All in all, the only way to look at Addiction is as both a psychological addiction AND a physical addiction that are inextricably liked through our psyche’s presence in the brain, a physical part of the body. It may seem like a small thing, but this distinction makes many users feel as if their problem is less, or more, sever than that of other addicts. As far as I’m concerned, if you have a behavior that is making your life miserable and which you can’t seem to stop, it doesn’t matter if you’re throwing up during withdrawal or not. It’s an issue and you need help.

Addiction-brain effects – Tolerance, sensitization, and withdrawal

If you’ve been with us for any length of time, you’ve already read about the addiction-brain effects for specific drugs. I think it’s important to understand some of the more general changes that occur in the addicted brain regardless of the specific drugs used.

One of the most common effects of long term drug use is something called tolerance, or the reduced effect of a drug dose. A lot of people know about this one, especially if they’re users and have found themselves needing to use more and more to get the same effect. However, while this is the most known, it is not the only change in the body, or brain’s, response to drugs with repeated use. The other effect, known as sensitization, is characterized by the exact opposite reaction – an increase in the response to the drug.

Tolerance & Withdrawal in the addicted brain

toleranceThe exact mechanism by which tolerance occurs is different for each drug, but the overall concept is the same. With repeated drug administrations, the body adjusts its internal processes in an attempt to return to its initial level of functioning. Drug use normally causes greater quantities of neurotransmitters like dopamine, serotonin, the opioids, and adrenaline to be present in the drug user’s synapses (see here for a review). The body counters this by reducing its own release of these chemicals, reducing the numbers of receptors that can be activated by the neurotransmitters, and increasing functions known as “opponent processes” that are meant to counter their activity.

The interesting thing about tolerance is that by reducing the level of these important neurotransmitters, addicts are left with another, possibly more important effect, which is the loss of the addicted brain’s ability to respond to any reward, including natural ones like food, sex, enjoying a good football game, or anything else. Essentially, this sort of cross-tolerance leaves the addict less able to respond to rewards in general.

The reduced response to drugs, and the corresponding changes in the body and brain’s own functioning, have long been thought to be a major cause of addiction. The withdrawal that results once drug taking stops is closely linked to the development of tolerance. Still, we now know that tolerance and withdrawal are not necessary, and certainly not sufficient for the development of addiction. Nevertheless, they are referred to as the physical dependence portion of addiction and are often are part of the overall picture.

Sensitization

Sensitization is the term used for an increased response to the same dose of a drug. That might sound a little oxymoronic after the tolerance discussion we just had, but bare with me.

Tolerance commonly develops when drug use is constant, or ongoing. It’s an aspect of chronic, long-term, use. On the other hand, sensitization is likely to occur when a user engages in intermittent, binge-like, drug use happening either once daily, or with even greater spacing (as in once every few days) and in large quantities. When you combine chronic use with binge behavior, you can actually get both responses.

Sensitization to drugs has been shown for physiological responses like heart-rate, blood pressure, and movement in animals and humans. More importantly, sensitization plays a part in increasing the motivation for drug use. Just like sensitization increases the physical response to drugs, there is a corresponding increased response in the addicted brain in areas important for motivation (like the NAc and VTA for instance). If an addict responds more to their drug of choice after repeated use, it should come as no surprise that sensitization has also been hypothesized to play an important role in the addiction process.

Drugs cause brain changes that drive addiction

opponent processesWhen both tolerance and sensitization develop in someone who has been using drugs, they’re left with a reward system that is less responsive to rewards in general while being more responsive to the drugs they’ve been binging on and to cues (or triggers) that are associated with those drugs. If that sounds like a recipe for disaster, it is. If you’re an addict yourself, you don’t have to imagine this, you’ve lived it – A state where nothing seems rewarding without being high.

The problem is that both tolerance and sensitization are examples of changes in response to drugs that are completely outside of the control of the user. There’s no doubt that the average drug user doesn’t think about, or even recognize, that as they continue to use drugs, their body adjusts in multiple ways that can make it that much harder for them to stop use at a later point. It should be clear that this is not an issue for everyone – both tolerance and sensitization require repeated administration of drugs that are pretty close together. But they don’t require hundreds of uses, a few days with continuous, or intermittent use, are often enough to bring about these changes in the addicted brain.

We often hear that even the first hit of a drug can cause someone to be addicted. While there’s little doubt that even a single drug administration can change brain response in important ways, I can say with absolute certainty that using a drug repeatedly cause long-lasting changes in the brain chemistry that make future drug use more likely.

Addicts’ brains depressed but normal users… normal.

A paper that’s about to be published in the journal Science has found at least part of the difference between the brains of addicted individuals and those that use recreationally.

The question as to why only some people get addicted to drugs has been a difficult one to answer. Still, there’s no doubt that only a relatively small fraction of those exposed to drugs develop the compulsive, often destructive pattern of use we associate with addiction. The pattern holds in animal research too – even though all the animals in an experiment get the same amount of drugs, delivered in the same way, only some of them develop addictive drug taking. It seems there’s something different about addicts’ brains, but what is it?

What’s different about addicts’ brains?

We’ve found quite a few things that differentiate addicts’ brains from those of normal research participants. These include lower density of a certain type of dopamine receptor (D2), reduced activity in specific brain parts like the OFC (orbitofrontal cortex) that are important in decision making and behavioral control. Still, if we start with what is supposed to be a pretty similar group of rats and give them all the same drug, for the same time, in the same amounts, why do only some get addicted?

This recent study found that a specific neuronal process called LTD (Long Term Depression), that is important in learning (or what we call plasticity) is suppressed in addicted animals for far longer than in animals that end up not not displaying addictive behavior. Even though all animals displayed this sort of deficiency in LTD right after learning to take drugs, only the addicted animals showed it when tested two months later.

Since the difference was seen in an area of addicts’ brains called the Nucleus Accumbens, a very important area for learning about rewards, it seems likely that it plays an important role in addicts’ inability to change their behavior after they’ve started using drugs. Past research has already identified this as a problem with something we call “reversal learning” but it seems we may have just found at least part of the mechanism.

Now we have to figure out why some animals show this sort of pattern and others don’t. Genetic variability seems like a good place to start here.

Citation:

F. Kasanetz, V. Deroche-Gamonet, N. Berson, E. Balado, M. Lafourcade, O. Manzoni, P. V. Piazza, Transition to addiction is associated with a persistent impairment in synaptic plasticity. Science 328, 1709–1712 (2010).

Obesity, drug addiction, and dopamine

Eating junk-food can be addictive, and apparently, it causes brain changes that look eerily similar to drug addiction. That’s the message not only from the rapidly fattening waistlines of Americans everywhere, but also from the Johnson and Kenny labs at the Scripps Institute.

Food and drug addiction

The idea that obesity is caused by a compulsive pattern of eating, and that there could be a similarity between such compulsive eating and drug addiction isn’t super new. In fact, Dr. Volkow from NIDA seemed to make research into this association her goal when taking  the helm of the addiction research kingdom.

When you think about it, the notion isn’t far-fetched: Drug addicts continue to take drugs, in increasing amounts, even though they’d often like to stop (at some point) and in the face of negative consequences and the common loss of other important life functions (like family, work, etc.). Obese individuals are quite the same, eating more and more food regardless of their desire to adopt a healthier diet and in-spite of ridicule, low self-esteem, and decreased functioning that often accompanies extreme weight gain.

The research by Johnson and Kenny examined whether exposure to the kind of high-fat, super high-calorie foods that floods the junk-food market are responsible for creating food-addicts in a similar way to drugs that alter the brain in ways that make stopping more difficult.

Dopamine, reward, and junk-food

The study took three groups of rats and gave them either the regular chow diet lab animals are used to or the worse kind of birthday party food: bacon, sausage, cheesecake, pound cake, frosting and chocolate. You can imagine the party going on in the rat cages that got to eat that! Of the two groups that got to eat the crazy-fat food, one had unlimited access while the other got to binge for only one hour a day.

The bottom line: Only the rats that got unlimited access to the fat-party food developed compulsive eating habits that resulted in roughly twice the weight gain of the other two groups and the ability to continue eating even in the face of signals for punishment (a light that they were trained to associate with shocks).

When the researchers looked deeper, they found that the brains of these rats suffered a significant reduction in the density of a specific kind of dopamine receptor (D2) in a brain part known as the striatum, the same kind of reduction common in drug addicted people and obese individuals. This receptor type is often thought to be important for regulation of impulses, both physical and otherwise. It therefore makes sense that losing this type of function would cause uncontrollable eating or drug taking.

Are drug- and food-addictions the same?

While this research isn’t saying that compulsive eating, or obesity, are the same as drug addiction, it does strongly suggest that there are common mechanisms in both. More importantly, it reveals a common process that unfolds when over-exposure to the reward, in this case food, occurs. This tells us that there can likely be common pathways to these different addictive disorders, though whether any specific person ended up a food- or drug-addict because of this kind of process is still an open question. I wonder if we’ll see something like this with sex addiction soon…

Citation:

Johnson and Kenny (2010) Dopamine D2 receptors in addiction-like reward dysfunction and compulsive eating in obese rats. Nature neuroscience, 13, 635-641.