Why do we move? The brain as a reward optimization device
We humans are creatures somewhere over a meter tall, weighing a few dozen kilograms, and without any remarkable physical features, but depending on how you look at it, we are also creatures who have the history of the globe woven into us, in a certain sense.
All creatures have evolved since the age of bacteria so that they are certain to survive.
We have evolved by how efficiently we can obtain rewards and survive using limited energy and time—that is, the functions of all creatures on earth have changed, developed and optimized with “survival” as a keyword—so what functions have humans obtained to survive?
Big fangs and quick legs are probably necessary, but it is also necessary to optimize behavioral patterns to use limited resources effectively.
Maintaining interest in food even when you are full and wandering around in search of prey will cause a loss of energy, while remaining unmotivated when hungry even though prey is nearby is also a serious loss of opportunity.
In other words, our behavioral patterns need to be optimized for the reward and according to the situation we are placed in for our behavior to be optimized. What mechanism is this controlled by?
Noradrenalin as a reset device
The paper I discuss today hypothesizes that noradrenalin, which is secreted by the locus caeruleus, the nucleus of the rewards system in the brain, is strongly related to behavioral optimization.
This paper discussed studies on various small animals and primates and shows based on various research outcomes that:
- noradrenalin secretion patterns change with changes in behavioral patterns; and
- these changes in secretion patterns are associated with changes in activity in the prefrontal cortex (the heart of behavior control) and changes in behavioral patterns.
Specifically, the locus caeruleus, which secretes noradrenalin, has two behavioral patterns: phasic mode, in which behavior increases transiently when an unfamiliar stimulus appears, and tonic mode, in which behavior increases permanently when the same stimulus presents repeatedly over a long time. The paper shows that the former encourages appropriate behavior, while in the latter, appropriate behavior decreases and behavioral patterns suggesting that concentration had been lowered appear.
Thus, by changing secretion patterns, noradrenalin secreted by the locus caeruleus can motivate the individual to seek out rewards when they are needed and actively lower attention and concentration on rewards when they are sufficient, thereby enabling resources to be allocated to other goals.
In other words, noradrenalin acts like a reset button to switch behavior according to the situation, but it is known from experience that information processing capacity can change according to the level of arousal in hemispatial neglect observed in dementia or stroke patients. I wondered whether it might be best to keep the mechanisms of neurotransmitters relating to the rewards system in mind when thinking about cognitive and executive functions in a clinical setting.
Reference URL: Network reset: a simplified overarching theory of locus coeruleus noradrenaline function
