Neuroscientist Daeyeol Lee of Yale University registered activity of single neurons in the human volunteers’ brain (amygdala) while images of junk food were presented. About 31 % of all registered neurons were increasing their activity in a predictable way as the individual value of a food increased though there were other neurons in the same region, which activity declined as the value of a food increased (J Neuroscience, January 5 , 2011).

Interestingly, the amygdala is a region that is traditionally associated with memory of emotions, mostly fear and aversive reactions including immobility, tachycardia, increased respiration, and stress-hormone release (”Cytoarchitectonic mapping of the human amygdala, hippocampal region and entorhinal cortex: intersubject variability and probability maps”. Anat Embryol (2005) 210 (5-6): 343–52). However, it’s been shown to participate in the process of Pavlovian conditioning with food as a positive reinforcement (Nature  2005, 439 (7078): 865–870)