Spoiled Reward-Pathway Hypothesis

From: Philip Jonkers (P.A.E.Jonkers@phys.rug.nl)
Date: Fri Aug 17 2001 - 17:22:43 BST

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    From: Philip Jonkers <P.A.E.Jonkers@phys.rug.nl>
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    Subject: Spoiled Reward-Pathway Hypothesis
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    The Spoiled Reward System 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.

    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 motivator designed to maximize chances of
    survival and as such, maintain biological evolution.

    With the 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 emissions of feelings of rewards
    to its partakers. The RP was obliged to take up the dual task of
    rewarding biological as well as cultural actions. Therefore, in humans,
    the RP is the built-in motivator of both genetic and memetic evolution.
    The main objective of life, survival, was 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 serving parties
    of biology and culture, it is plausible also to assume that the RP is
    used to receive many stimuli. 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 from performing regular healthy biological and cultural actions
    (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 beneficial activities.
    After all, scarcity of resources forced competitive selection necessary
    to fuel evolution in the first place. The unfortunate people with a lack
    of healthy supply of satisfaction are still left with a spoiled
    RP inherently craving for stimuli.

    To satisfy themselves (by satifying their spoiled RPs) they have the
    tendency to seek pleasure and reward in artificial and most of the times
    harmful means. The consensus now is that drugs, gambling, compulsive sex
    and eating all have in common to stimulate the RP. This is where the risk
    of addiction kicks in. Needless to say, addiction is wide-spread and
    highly prevalent among all layers of the population (e.g. work can
    become addictive too). The mentioned surrogate means stimulate the release
    of dopamine. Normally this NT/hormone is necessary for re-inforcing
    healthy behavior by helping to memorizing it. (Dopamine has a stabilizing
    role on memory.) Unfortunately, the above mentioned artificial means have
    a similar effect and increase the risk of addiction by re-inforcing
    the corresponding unhealthy behavior thus making recurrence probable.
    NB Bear with me that I just started out in neuroscience so I might fall
    a little short on accuracy.

    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?


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