Antireward: The sly system that keeps you addicted

Addiction–behaving in a way you don’t want to compulsively–can cause extreme suffering, to those who are addicted and to people around them.

Sometimes the suffering is not so extreme, as with my morning cup of coffee. I wake up tired and headachey, but soon those feelings are replaced with a sense of energy and possibility, all due to that lovely cuppa.

I am certainly addicted to caffeine, but it’s not the energy it gives me that keeps me pouring cup after cup each morning. No, there is something more insidious at work: the antireward system.

What exactly goes on in the human brain that makes it susceptible to addiction? One function of humans you may not know about that contributes to addiction is the antireward system.

Homeostasis vs allostasis

The human organism is an amazing thing, equipped with homeostatic processes designed to keep it functioning in a more or less healthy range. The latest research and theories suggest that addiction develops through the dysregulation of a homeostatic hedonic mechanism involving the reward and the antireward systems. Addiction happens when your brain tries to keep your pleasure level constant (the happiness setpoint), but it ends up in a downward spiral.

Addiction can be considered an allostatic mechanism, rather than homeostatic. Homeostasis refers to a biological system’s ability to maintain a dynamic internal equilibrium in response to external or internal changes. Allostasis uses change to achieve some level of stability in the face of external or internal changes too large to be accommodated with homeostasis. Allostatic processes respond to more intense challenges than to the relatively subtle changes that homeostatic processes respond to. And allostatic states represent a state of chronic deviation from the normal setpoint.

There is controversy over whether addiction should be considered a disease or not. In many ways, the allostatic framing of addiction does suggest it as a pathological brain state, one which doesn’t represent normal brain functioning.

The antireward system

The use of a psychoactive drug over time is a challenge that the human brain responds to with enduring changes in the reward system and the antireward system. The antireward system compensates when the reward system is overtaxed.

There are two processes at work in responding to repeated consumption of a very rewarding substance (or behavior) (Solomon, 1980):

  • Process A, the positive response to drug intake, which occurs quickly and dissipates quickly. A tolerance develops. For example, you may find that over time you need more cups of coffee each morning to get the same effect as when you first started drinking it.
  • Process B, the more sluggish development of withdrawal effects. You won’t feel caffeine withdrawal if you’ve only just started drinking coffee. But once you’re an established coffee drinker you’re likely to get headaches and feel lethargic if you go without.

Process A represents the reward system. Process B is the compensatory antireward system, which is your body’s attempt to bring yourself back to hedonic neutrality.

Unfortunately, these interacting processes leave you compulsively seeking your drug of choice, to get rid of the negatively reinforcing withdrawal state.

In the brain, these processes reflect  the functioning of two separate systems (Koob & Le Moal, 2008):

  • Process A reflects your dopamine and opiate responses, which downregulate over time (making you require more and more of the drug to get a positive effect)
  • Process B reflects your sensitized stress response system (specifically corticotropin releasing factor upregulation), making you feel anxious and distressed without your drug of choice on board

If you use a psychoactive substance on a regular basis, you will experience your hedonic allostasis mechanism making you more and more miserable, as shown in the conceptual graph below:

addiction-allostasis

from Koob, 2013

Each consumption of the drug launches Process A, but the reward you get from it is decreasing with each time you consume it again. Process B acts to counteract the increase from your set point, and through its slow moving ways, decreases your set point (i.e., your mood) over time.

This theory explains the research evidence that while either positive reinforcement (seeking a positive reward) or negative reinforcement (acting to eliminate something negative such as anxiety) can drive compulsive drug use, though negative reinforcement is much more prominent and powerful as a driver of use (Kassel, 2010).

The implication for getting a handle on addictive behavior is that you need to pay as much attention to your antireward system as to your reward system.

Why do I love coffee so much?

I love it so much because it takes away the feelings of caffeine withdrawal. But if the process of addiction is as I’ve sketched out here, my daily consumption of it is probably making me feel worse at baseline and on average than I would if I didn’t drink coffee at all, or drank it only occasionally.

This is important for emotional health, as psychoactive addictive substances like caffeine, and more dangerous ones like alcohol or opiate drugs, can drag down mood over time, leading to worsening mood.