Tuesday, November 14, 2006

Dopamine and Preparedness

Dopamine and Preparedness.

Andre Willers
14 Nov 2006

Sources : see at the end.

Dopamine acts as a proximal reward . ie a Pleasure system
An organism anticipating a distal reward ( far off in time ) secretes dopamine as a proximal and immediate reward to bring all its systems into a state of preparedness . The greater the uncertainty , the greater the activation of preparedness needed .

The classical experiment :
A light flashes . The rat presses a lever and is rewarded . The dopamine levels are measured during the whole process .

The results showed that after the rat learned the response after a few passes . On the next pass , dopamine levels peaked before the lever was pressed , then peaked again higher after the lever was pressed and before the reward was given . In other words , the anticipation triggered the dopamine release .

If the reward was given on random basis , the release of dopamine peaked even higher when the probability of reward was 50% . In other words , when the uncertainty of the reward-state was at a maximum .

Ie if no reward is given 60% of the time , the rat is certain that he getting no reward 60% of the time . The uncertainty is then 40% . The maximum the uncertainty can be is 50% . The rat trains on the highest percentage .

This also means that the organism must be at it’s most prepared when the uncertainty of the reward is at its maximum . If the reward is going to fall into his mouth with no effort , no preparation is necessary . Likewise if there is going to be no reward . In between , it must be prepared , and the maximum preparedness is needed at 50% uncertainty .

Hence the maximum dopamine levels are at a maximum when the reward percentage in an on-off system is 50% .

In queuing theory this would be the equivalent of how the queue is ordered , since the most prepared would usually have the first place in any queue .

The proximal pleasure argument should hold in any species that is subject to evolutionary pressures . So any aliens even vaguely like us will have similar activation responses , (and similar drugs like cocaine , etc.) . They will also gamble and flirt .

The relevance to human systems .

The fact that intermittent rewards leads to higher dopamine levels (pleasure) than straight rewards has major implications for gambling , personal goals , depression , sports or any competitive endeavour .

Flirting is an extremely good example . It is an essential activity in any species with more than one sex . Some human societies even have professional flirts ( called marriage brokers or marriage makers ) .
It optimizes genetic mixes . A single female can keep large number of males on a personal string , thereby dramatically enhancing the probability of success of her offspring once she makes a choice .

The above argument seems to species independent .

Flirting in self-aware species with three , four or more sexes should be fascinating . Humans with two sexes are complex enough , but the mind boggles if there are more sexes . Though , since this process is one of the driving forces of evolving intelligence , one would expect humans to be evolving more than two sexes : see “The Sexes of Man” in http://andreswhy.blogspot.com

Reward scale:
There is a complicating factor , namely that the scale of reward might play a role in dopamine release . But the nervous system evolved as an on-off system and is notoriously bad at estimating scales . Eg gamblers will bet on anything , regardless of scale . Risk-reward odds are ignored or poorly done .

A Simple visual Dopamine stimulator .
(For a human)

In the classic Experiment above , just retain the anticipation (ie the flashing light . ) Tell the subject he can expect a reward after the light flashes . Flash the light at around double Beta-brainwave frequencies ( 30 – 60 Hz) , with a 50% chance that the flash will show on the screen . On average the screen will show half the rate ( ie Beta-frequencies) .

Intended consequences:
This should flood the system with dopamines in the active , awake state .
It entrains the system at these frequencies , since the frequency of stimulation of the pleasure systems are associated with a particular brain-wave frequency .

The frequency of the flashes might have to be adjusted upwards (as sequential non-flash sequences of 8 to 10 are probable in 300 random runs , thereby bringing down the frequency in a sequence . The effect of this is unknown , but thought to be natural in a human system .)

This should kick-start an athlete before an effort . Depressives , alcoholics or cocaine-withdrawals should benefit . Natural child-birth mothers should benefit . a nice little pick-me-up on your screen-saver .

In general a good thing in moderation .
If the frequency is adjusted to (say) theta , the pleasure-entrainment will keep the subject unconscious (pain , etc)

Abuse .

This is a cheap high , but with a small half-life . A healthy system will quickly become habituated and adjust . The half-life is unknown , but the best estimate is about 1/e (about 33%) of other dopamine opiates .

Long-term abuse will lead to a half-life of 50%
(s= 1/3+(1.3)^2 + (1/3)^3 +…

Problems might arise in initial reward-stimulation .

Rull-type visual entrainment is at least 2 generations of thin-skin materials away .

Pillips P et al :” Subsecond dopamine release promotes cocaine seeking” Nature 422(2003)

Fiorillo C et al “Discrete coding of reward probability and uncertainty in dopamine neurons” Science 299(2003)
Sapolsky M “Monkeyluv : The pleasure and (pain) of Maybe”
ISBN 0 224 07365 6

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