the majority of these studies were conducted with adult male sprague - dawley rats from a selective - breeding colony which has been previously described14 .
selectively - bred rats from generations s18 , s20 and s21 were transported from the university of michigan ( ann arbor , mi ) to the university of washington ( seattle , wa ) for the fscv experiments . during each behavior session , chronically implanted microsensors , placed in the core of the nucleus accumbens , were connected to a head - mounted voltammetric amplifier for detection of dopamine by fscv23 .
voltammetric scans were repeated every 100 ms to obtain a sampling rate of 10 hz .
voltammetric analysis was carried out using software written in labview ( national instruments , austin , tx ) . on completion of the fscv experiments ,
recording sites were verified using standard histological procedures . to examine the effects of flupenthixol ( sigma , st .
louis , missouri ; dissolved in 0.9% nacl ) on the performance of sign - tracking and goal - tracking behavior , rats received an injection ( i.p . )
of 150 , 300 or 600 g / kg of the drug one hour prior to pavlovian conditioning sessions 9 , 11 and 13 .
doses of the drug were counterbalanced between groups and interspersed with saline injections ( i.p .
, 0.9% nacl ; prior to sessions 8 , 10 , 12 and 14 ) to prevent any cumulative drug effects . to examine the effects of flupenthixol on the acquisition of sign - tracking and goal - tracking behavior
, rats received an injection of either saline ( i.p . ) or 225 g / kg of the drug one hour prior to pavlovian conditioning sessions 17 .
detailed methods and any associated references are available in the online version of the paper at www.nature.com/nature .
 individuals make choices and prioritize goals using complex processes that assign value to rewards and associated stimuli . during pavlovian learning , 
 previously neutral stimuli that predict rewards can acquire motivational properties , whereby they themselves become attractive and desirable incentive stimuli . 
 but individuals differ in whether a cue acts solely as a predictor that evokes a conditional response , or also serves as an incentive stimulus , and this determines the degree to which a cue might bias choice or even promote maladaptive behavior . here 
 we use rats that differ in the incentive motivational properties they attribute to food cues to probe the role of the neurotransmitter dopamine in stimulus - reward learning . 
 we show that intact dopamine transmission is not required for all forms of learning in which reward cues become effective predictors . 
 rather , dopamine acts selectively in a form of reward learning in which  incentive salience  is assigned to reward cues . in individuals with a propensity for this form of learning , 
 reward cues come to powerfully motivate and control behavior . 
 this work provides insight into the neurobiology of a form of reward learning that confers increased susceptibility to disorders of impulse control . 
METHODS SUMMARY
Supplementary Material