motivation, reward & addiction Feb 20, 2009

..or why we play the lottery anticipation, outcome and experience Breiter et al, 2001

what motivates us to eat? escape from hunger pleasurable (olfactory) experience boredom etc…..

drive-states:

hypothalamus, limbic system and beyond… influence of learning and emotion on goal-directed behavior - motivation by pleasure? Kelley 2004

addiction hijacking of the natural reward processes

movie time

how do we become addicted? DEPENDENCE need for continued exposure to a drug so as to avoid withdrawal symptoms dependence occurs as a result of adaptive changes in the body (homeostasis?) “cravings” (induction of a drive-state?) does dependence = addiction? (Nestler 1992)

simple homeostasis molecular / cellular models of tolerance & dependence

from dependence to addiction why are some abused drugs not addictive? is there a common “addiction mechanism”?

electrical self-stimulation

drugs kill “a hungry animal often ignored available food in favor of the pleasure of stimulating itself electrically .... 2000 times per hour for 24 consecutive hours” (Olds 1956)

“pleasure centers”

DA neurons and reward VTA (Schultz et al, 1993)

does DA signal reward? displacement of [11C]raclopride binding by DA release (Volkow et al, 1997) PET scan MP = methylphenidate “RITALIN”

learned associations not so fast…… DA activity is altered by experience

prediction errors novelty VTA DA response is associated with sensory cues i.e., DA response predicts reward drive is to correct error (Schultz et al 1997)