"We converted something that wasn't pleasing to something that suddenly became pleasurable, and when we did that the neurons we were studying switched their response," says senior author J. Wayne Aldridge, Ph.D., a research associate professor in the Department of Neurology at the U-M Medical School. "Pleasure has traditionally been one of the hardest problems for neuroscience to measure, but these results shed light on how it is represented in brain activity."
The study was designed so that the signals from the ventral pallidum were only related to the "liking" ?or disliking ?of the taste, and not to a salt-seeking drive or movement. The ventral pallidum is part of the limbic system of the brain, which is involved in motor-muscle control as well as pleasure and reward.
In an accompanying editorial, University of North Carolina researchers Robert Wheeler and Regina Carelli call the study "elegant" and the results a "profound step" toward understanding the nature of pleasure itself, rather than the behaviors and actions triggered by it.
Aldridge collaborated on the study with former U-M Psychology graduate student Amy Tindell, Ph.D., and with Kent Berridge, Ph.D., a professor in the Department of Psychology in the College of Literature, Science, and the Arts.
"This finding reveals a type of brain Morse code for pleasure," says Berridge. "The faster these neurons fire, the more pleasant the taste seems to become. The hardest test for a pleasure code is whether the brain signal can track the change from nasty to nice. The amazing fact is that these neurons pass that test."
Aldridge notes that an analogous effect occurs in everyday human life, when a formerly favorite food becomes less attractive after we have over-indulged in that food.
"Moment by moment, this low-level information processing in the brain helps us react t
Source:University of Michigan Health System