The Neural Basis of Perceptual and Cognitive Pleasure

Irving Biederman
University of Southern California


Where we look with our next fixation or our selection of which movie to see or book to read is decidedly non random.  What controls this selection when an individual is not hungry, avoiding harm, engaged in deliberate search, etc.?  And how can the selection be manifested in real time, at the rate of three visual fixations per second?   The surprising discovery of a gradient of mu-opioid receptors (possible ligand termed "endomorphin") in the macaque ventral cortical visual pathway, a system presumed to subserve visual recognition, may provide the key for understanding the spontaneous selectivity of perception and thought.  These receptors are sparse in the earliest stages, e.g., V1 and V2, but dense in the later stages (parahippocampus), where perceptual information activates the products of past experience. A simple mechanism may account for a vast range of spontaneous perceptual selectivity: Experiences are preferred that maximize the rate of endomorphin release. Such inputs will tend to be those that are richly interpretable (not just complex) insofar as they would produce high activation of associative connections in areas that have the greatest density of mu-opiate receptors. Once an input is experienced, however, competitive learning would serve to reduce activity, resulting in less endomorphin release, leading to habituation and boredom. Ratings of scene preference and their decline with repetition reliably correlate with fMRI activity in the parahippocampal gyrus during passive 1 s viewing of scenes.  These are not feedforward effects in that nonpreferred and repeated scenes produce equivalent activity in more posterior areas associated with early visual processing and attention.  Because this system is never satiated and it maximizes the rate at which we acquire new but richly interpretable information, it renders us infovores.