A Phil-for-an-ill Blog

September 1, 2008

The Spoiled Reward Pathway Hypothesis

I wrote the next piece just prior to going to the US to work as a neuroscience postdoc shortly after 911 (October 2001). It was a time when I was all hung-up over evolution theory in general, and memetics in particular. The subject of this treatise is a speculation on the idea of the reward pathway of the brain growing in size and significance together with brain in the process of our human (presumed) evolution.

The Spoiled Reward Pathway Hypothesis

Susan Blackmore makes a solid case in defending and describing the hypothesis of the emergence of humans’ big brains as a result of cultural and biologically coupled evolution, she refers to this process as gene-meme co-evolution [2].

The original biological function of the reward pathway (RP) – running from a brain stem ventral tegmental area (VTA) via the nucleus accumbens (NA) to the prefrontal cortex – is to issue feelings of reward for fulfillment of actions aimed to warrant or enhance chances of survival such as eating, drinking and reproduction. Without the RP organisms would lose interest in life and be rendered incapable of maintaining self-support as life-saving or reproductive activities would not be re-inforced by the act of reward. Therefore, the RP is the built-in motivator designed to maximize chances of survival and as such, maintain the process of biological evolution.

With the historical arrival of culture and its (initial) biologically advantageous and useful role in survival, the RP had to take up an additional task of rewarding actions aimed at developing and maintaining culture. I contend that the gene-meme co-evolution could not have been sustained if such actions were not accompanied by the release of feelings rewards similar to a purely biological evolution. The RP was therefore obliged to take up the dual task of rewarding biological as well as culturally oriented constructive behavior.

Therefore, in humans, the RP is the internal motivator of both genetic and memetic evolution. The raw biological objective of life, survival, was thus supplemented with a myriad of cultural sub-objectives, some of which are only remotely related to survival at best (such as art, music, dance). Together with the increase in brain size it seems plausible then, that the RP gained in size simultaneously. At present stage of brain evolution, by catering to both biology and culture, it is plausible also to assume that the RP is used to receive many stimuli at least, relative to the animal RP. Therefore, compared to non-human organisms one might say that the human brain RP is spoiled.

In healthy human beings the RP serves its role well by providing sufficient satisfaction for the performance of regular and healthy biological and cultural behavior (such as work, school, sports and so on). Since the resources on this planet are limited however, not everyone gets the opportunity to derive sufficient satisfaction and pleasure from such activities. After all, scarcity of resources forced competitive selection necessary to fuel evolution in the first place. The unfortunate people with a lack of a healthy supply of satisfaction are still left with a spoiled RP inherently craving for stimuli.

In order to be able to satisfy themselves (by satifying their spoiled RPs) they may have the unhealthy tendency to seek pleasure and reward in artificial and most of the times harmful stimuli. The consensus now is that drugs, gambling, compulsive sex and eating all have in common to unilaterally stimulate the RP. This is where the risk of addiction kicks in, I believe. Needless to say, addiction is wide-spread and highly prevalent among all layers of the population (e.g. work can become addictive too, or even the much sought after successful career). The mentioned surrogate stimuli encourage the release of dopamine. Normally this NT/hormone is necessary for re-inforcing healthy behavior by helping the brain to memorize it. (Dopamine has a stabilizing role on memory.) Unfortunately, the above mentioned artificial stimuli have a similar effect and thus increase the risk of addiction by re-inforcing the corresponding unhealthy behavior and making recurrence progressively probable.

In conclusion, I contend that the wide-spread prevalence of addictive behavior is an artifact of the meme-gene co-evolution of the brain (and in particular the RP).

Anyone, any comments?

Consistent with the ideas presented above, addiction in animals living in a natural environment is very improbable. Does anybody know of cases reporting animal addictive behavior?



1 Comment »

  1. Hi all!
    Nice site!


    Comment by accerpedyUnap — October 1, 2008 @ 3:51 pm | Reply

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