Research ProjectsWhat's the picture at right?
'Liking' - Brain pleasure systems:

What brain systems generate sensory pleasures? We have identified opioid neurotransmission in the brain nucleus accumbens and ventral pallidum, GABA feedback on to spiny GABA neurons in accumbens shell, and cannabinoid transmission in nucleus accumbens as crucial for causing 'liking' for taste pleasure. 'Liking' is an objective process of positive hedonic reaction that underlies subjective sensory pleasure. To gain windows into 'liking' reactions, we analyze facial affective expressions that are homologous in human infant, non-human primates, and even rodents (Infant/primate sample PDF; Expression overview PDF). Combining natural expression windows into 'liking' with neuroscience techniques, we study brain mechanisms that cause pleasure 'liking' ('Liking' research sample PDF; Pleasure overview PDF).


'Wanting' - Incentive Salience
How does reward 'wanting' relate to reward 'liking'? A common brain myth is that dopamine mediates sensory pleasure, but our research helps indicate that dopamine mediates only a form of ''wanting' called incentive salience, and not pleasure 'liking'. Our goal is to better understand the psychological nature of incentive salience and to clarify its brain mesolimbic mechanisms. To study the role of dopamine in 'wanting', we use three biopsychology techniques: (1) Neurochemical manipulation of dopamine, (2) Hyperdopaminergic DAT-knockdown mutant mice (in collaboration with Xiaoxi Zhuang at U. Chicago), and (3) Electrophysiological recording of neurons in the limbic system (with J. Wayne Aldridge).

(Mutant Mice sample; 'Wanting' overview 1 ; 'Wanting' overview 2 ).


Function of the Ventral Pallidum
We are seeking to elucidate the neurochemical mechanisms of motivated behavior in ventral pallidum, a limbic output structure known to be crucial for normal ‘liking’ and ‘wanting’. In addition to pharmacological manipulations of ventral pallidum receptors, we collaborate with J. Wayne Aldridge and Amy Tindell to determine how these neurons electrophysiologically code the hedonic impact of tastes ('liking'), the attribution of incentive value to reward cues, and the motivation to pursue rewards ('wanting'). We are also examining how opioid systems in ventral pallidum, lateral hypothalamus and nucleus accumbens interact as a circuit to cause taste ‘liking’.
(VP research sample
).


Affective valence in limbic microcircuits
What determines if something is nice or nasty? What does desire share in common with dread? We are examining brain maps of affective valence (positive versus negative emotion) in the nucleus accumbens. Our work has found rostrocaudal gradients of ‘liking’ and ‘disliking’ in accumbens shell. We are also examining the role of accumbens microcircuits that serve as building blocks of motivational salience that the brain can construct into either desire or dread. This may have important implications for understanding ordinary positive and negative affective reactions in normal people, and for some pathological affective reactions in schizophrenia and other clinical disorders (Valence research sample 1 ; Valence research sample 2 ).



Addiction
Why is drug addiction so compulsive and long lasting? The distinction of 'wanting' from 'liking' has important implications found in the Incentive-Sensitization theory of addiction
. Addictive drugs can cause permanent neural sensitization in brain mesolimbic systems of incentive salience. Sensitized incentive salience means addicts have compulsive 'wanting' to take drugs, which can last months or years. Much neuroscience evidence has emerged to favor this theory in the 10 years since it was first proposed. We stress Incentive-Sensitization theory does not provide a cure for addiction, but it does help pinpoint a crucial aspect of what goes wrong. That understanding may eventually aid design of a more adequate cure. Basic affective neuroscience research on ‘wanting’ and ‘liking’ in our lab aims to better understand underlying mechanisms, which we hope will have direct implications for understanding addiction (Incentive sensitization research sample ).
Other Human Applications
Incentive salience 'wanting' mechanisms have implications for other forms of human irrational desire (Irrational choices
). We are also exploring how basic 'liking' / 'wanting' systems may relate to conscious and unconscious emotion processes in normal people (Unconscious emotion; see also Piotr Winkielman's web page).