“Dopaminergic reward signals selectively decrease fMRI activity in primate visual cortex” [Subscription required]
Article excerpt with my emphasis “…the highly selective behavioral and neural effects induced by stimulus-reward pairings must be reconciled with the apparent widespread and diffuse nature of neuromodulatory reward signals. A potential explanation for this seeming contradiction is that selectivity arises through an interaction between a broadly distributed reward signal and coincident bottom-up, cue-driven activity. In this way, a diffuse dopaminergic reward signal is rendered selective, allowing reward to specifically modulate activity within reward-predicting cue representations.”
My comment: In my model selectivity associated with visual stimulus-reward pairings arises through the interaction with olfactory input and its bottom-up epigenetic effects on the microRNA / messenger RNA balance, which are controlled by the epigenetic effects of pheromones from the top-down. The molecular mechanisms for this are conserved across species as per Darwin’s nutrient-dependent “conditions of existence’ that precede control of reproduction by the metabolism of nutrients to pheromones.
In some insects, the dopaminergic / serotoninergic balance enables nutrient reward selectivity so that toxic plants are avoided and pollen with higher nutritional value is selected (e.g., in honeybees). In humans, Buspirone functions as a serotonin 5-HT1A receptor partial agonist that supposedly mediates its anxiolytic and antidepressant effects. Additionally, it functions as a presynaptic dopamine agonist D2,D3, dopamine antagonist D4, as well as a partial α1 receptor agonist.
In humans, after ruling out effects of dopamine, oxytocin, and serotonin, it was reported that “…the most important genetic effects on attachment might be hidden in interaction with environmental factors….[and that] …epigenetic processes merit consideration, as these can modify gene expression and neural function without changing nucleotide sequence….”
Excerpt: Once rhesus monkeys learn to associate a picture with a reward, the reward by itself becomes enough to alter the activity in the monkeys’ visual cortex.