Amygdala Function and Addiction

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Amygdala Function and Addiction

We have known for a long long time that stress will make people break their commitments to staying sober or to quit smoking. And at some intuitive level we have an understanding of why this would be the case: It just seems easier to maintain your plans and promises if you are at full capacity and not distracted by stress, negative thoughts, pain, hurt or humiliation. But for a long time there was not a lot of science backing up this assumption. That is slowly changing now.

The research is now more focused on self control efforts and self regulation and how that is exercised by the PFC or prefrontal cortex. This effort will suppress instinctive and habitual behavior of amygdala. Or at least modify the way that amygdala and the rest of the limbic brain controls behavior. The limbic brain is the seat of anything that is instinctive and any natural desire. This includes thirst, hunger, fear which are inborn urges. It also includes urges towards gambling, drug taking and other behaviors that are learned versions of the basic instinctive behaviors. So understanding the way that amygdala can be controlled is central to understanding addictions and unwanted habits.

The ability to self-regulate can become impaired when people are required to engage in successive acts of effortful self-control, even when self-control occurs in different domains. Here, they used functional neuroimaging to test whether engaging in effortful inhibition in the cognitive domain would lead to putative dysfunction in the emotional domain.

Finally, depleted participants showed reduced functional connectivity between the left amygdala and ventromedial prefrontal cortex during negative scene processing. These findings demonstrate that consuming self-regulatory resources leads to an exaggerated neural response to emotional material that appears specific to negatively valenced stimuli and further suggests a failure to recruit top–down prefrontal regions involved in emotion regulation.

Ego depletion or decision fatigue happens when you strain your brain for a period. The effect of ego depletion is to make it less likely that you do more things that will deplete you. Its a kind of limitation on your ability to anything other than what comes naturally to you. Making a decision will deplete your ressources. Controlling your emotions or your bodylanguage will deplete you. Overcoming fear will deplete you.

Normally your behavior is the product of a constant negotiation between you predispositions and your conscious control. In terms of brain structures, your behavior is determined by the constant negotiations between your amygdala – representing your instincts and habits – and your prefrontal cortex, representing your rational control and conscious planning. Mostly you can override your feelings of insecurity, as when you approach a stranger and ask for directions. But sometimes you will find that you are not in control. Or rather that your prefrontal cortex is too weak to overcome resistance from amygdala. You might see someone famous that you actually admire, but instead of saying something nice you look at your feet, while cursing at yourself. It works the other way round too, as when your desires prompt you to do something which is counter to your plans and your rational thinking. You might have planned a few weeks of caloric restriction, but your limbic brain is “voting” for a quick relapse. You might be committed to staying sober, but your cravings suggest that you pop a bottle open or find some of your drug of choice. The constant question is which one is stronger, your limbic structures and instinctive urges or your rational planing and rational control.

This is the central question when we try to understand self control: Which part of you will dominate: your rational control (prefrontal cortex) or you instincts, habits and desires (the limbic brain, especially amygdala)? We used to think that people either had a strong or a weak “character”, and that willpower, self control and behavioral control was something rather constant and a reflection of your “personality”, whatever that was. But it got a bit more complicated when ego depletion was discovered in the late 90ties. It turns out that we are all quite strong willed, but that we all get rather weak willed after a while, as we make use of our ability to dominate our natural dispositions.

This understanding is now known scientifically as the “resource model” of self control and more colloquially as our tendency towards brainfade. According to the resource model the ability to regulate thoughts, behaviors and emotions draws upon a domain-general limited resource. Over time this resource becomes depleted and self control becomes less frequent and uncontrolled behavior driven by desire and cravings takes over.

In this study, they used functional neuroimaging to investigate the effects of this depletion on the brain as viewed in Phillips Achieva 3.0 fMRI scanner. They used the scanner to take pictures of the neural responses to emotional provoking material. They used a set of negative pictures with material that normally makes people respond emotionally. The question was: Would the prior depletion have an effect on the intensity of the response in the amygdala. If so, if the amygdala would light up stronger when people were depleted, that would confirm what we know intuitively: That stress favors relapse into unwanted habits. It would also give us a more precise understanding of why this happens and how to prevent it.

Forty-eight participants viewed images of emotional scenes during functional magnetic resonance imaging in two sessions that were separated by a challenging attention control task that required effortful inhibition (depletion group) or not (control group). They were all made to watch the original depletion video. The people in the depletion group was told to inhibit reading the words while the control group were told that they could read the words or not.




So what did the researchers find?
Compared to the control group, depleted participants showed increased activity in the left amygdala to negative but not to positive or neutral scenes. Moreover, whereas the control group showed reduced amygdala activity to all scene types (i.e. habituation), the depletion group showed increased amygdala activity relative to their pre-depletion baseline; however this was only significant for negative scenes.
This confirms our initial assumption that stress favors relapse. And it tells us that the balance between the PFC and the limbic brain is at the heart of the prolblem of relapse. In normal circumstances the limbic brain is at a low boil and if the PFC is not compromised it is easy or at least possible to divert attention from urges towards plans. You get things done according to your plans and long term goals. You avoid the allure of shopping, eating, drinking or snorting.
On the other hand: After depletion, when your PCF is exhausted, the picture changes. Now you don’t have the same ability to suppress the urges and impulses from the amygdala. It also changes and enhances your negative reactions. You become more affected by irritants, stress and your disapointments in life. If your are in any way inclined to soothe yourself with drugs or alcohol, this situation favors a relapse. Sooner or later your behavior is turned towards the short term goal of finding relief from your sorrows.  You then shop, drink, eat or snort according to your personal dispositions.

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