Young adult stimulant users' increased striatal activation during uncertainty is related to impulsivity

Abstract

Background: Young adults who use stimulants (e.g., cocaine, amphetamines) are at particular risk of transitioning to dependence. Previously, we demonstrated increased risk-taking in young adults who had used stimulants (Leland, D.S., Paulus, M.P., 2005. Increased risk-taking decision-making but not altered response to punishment in stimulant-using young adults. Drug. Alcohol Depend. 78, 83-90). Since outcome uncertainty is a critical element of risk, we investigated whether such individuals have different neural responses to uncertainty than their stimulant-naive peers.

Method: Eleven young adults (age 18-25) who had used stimulants were compared with 11 age- and education-matched stimulant-naive controls using functional magnetic resonance imaging and a card prediction task with relatively certain/uncertain outcome conditions.

Results: The caudate, an area involved in processing salient events, was among those regions more active in users than controls in response to uncertainty. Personality measures revealed that users were more impulsive than controls, and that neural response to uncertainty in a number of areas, including the thalamus/caudate, was positively correlated with impulsivity.

Conclusions: These results are consistent with the idea that young adults who have used stimulants find uncertainty particularly salient, due in part to preexisting differences in impulsivity, and may be subject to more "action pressure" when making decisions under uncertainty. This neural and personality profile may constitute a marker for increased risk of stimulant use.

Figure 1

Behavioral performance on the card prediction task. (a,b) Reaction times were slower and more incorrect predictions made on uncertain trials than certain ones, but stimulant users performed similarly to controls in both conditions. (c) There was more response uncertainty as reflected by entropy calculations (see Methods and Materials) on uncertain trials than certain ones. Stimulant users had higher response entropy than controls overall but not as a function of trial certainty. Error bars indicate SE.

Figure 2

Activation related to uncertain-certain trials in stimulant users and controls. (a) Activation of the bilateral thalamus/left caudate in stimulant users > controls during action selection in the uncertain-certain contrast (p < 0.05, corrected cluster-wise). (b) Percent signal change for the activation in a was positively correlated with BIS-11 impulsivity scores in the 10 users and 8 controls for whom personality data were available.