Concept-matching in the brain depends on serotonin and gamma-frequency shifts

Abstract

A Eureka moment has three components--puzzle, solution and hedonic response (elation etc.). Puzzle and solution come together in the association cortex and are immensely variable from instance to instance. By contrast, the hedonic response is subcortical and almost one-dimensional; how is it triggered? It is triggered by the relation between puzzle and solution, a good fit or good match, like the relation between two words that rhyme. In 1999 J.W. Fost proposed that serotonin is a crucial agent; here it is proposed that a frequency-jump initiates the serotonin causal chain, as energy shifts from 20 to 40 Hz or some such jump. The hypothesis assumes that any discrete idea is embodied in a time-course of electrical and chemical changes in a network of neurons, and that keeping the idea in mind involves repeating more or less the same time-course over and over. If observed frequencies in the gamma range result from such repetition, the period for running the time-course once is of the order of 25 ms. Also accepted is the suggestion that, although the brain runs many processes simultaneously, in the conscious mind attention focuses on only one idea at a time; an attempt to "think of two things at once" actually results only in giving them attention alternately, with a repeat-time of the order of 50 ms and frequency 20 Hz. Only if the two time-courses have certain elements in common will there be any repetition at 40 Hz. Now suppose a thinker takes up a problem and makes a succession of attempts at solution. As long as he thinks of wrong answers, he generates activity only at 20 Hz, but when he hits upon the right answer, activity at 40 Hz shows up. This is a highly oversimplified scenario but its essential features might carry over to the vastly more complicated workings of a real brain. The virtue of the proposed mechanism is its generality. Under the proposal, any ideas in mind that do not match give no result but as soon as two ideas match, results ensue. This behavior in the model, wholly general except in one specific respect, is needed for conformity with real human brains' behavior. In normal people, production of this "link-joy" is an important reward mechanism and malfunction of this system may contribute to Capgras syndrome and some varieties of autism.