Cortical activation during delay discounting in abstinent methamphetamine dependent individuals.
BACKGROUND
Methamphetamine (MA)-dependent individuals prefer smaller immediate over larger delayed rewards in delay discounting (DD) tasks. Human and animal data implicate ventral (amygdala, ventral striatum, ventrolateral prefrontal cortex insula) and dorsal (dorsolateral prefrontal cortex, dorsal anterior cingulate cortex and posterior parietal cortex) systems in DD decisions. The ventral system is hypothesized to respond to the salience and immediacy of rewards while the dorsal system is implicated in the process of comparison and choice.


METHODS
We used functional Magnetic Resonance Imaging to probe the neural correlates of DD in 19 recently abstinent MA-dependent patients and 17 age- and gender-matched controls.


RESULTS
Hard DD choices were associated with greatest activation in bilateral middle cingulate, posterior parietal cortex (PPC), and the right rostral insula. Control subjects showed more activation than MA patients bilaterally in the precuneus and in the right caudate nucleus, anterior cingulate cortex (ACC), and dorsolateral prefrontal cortex (DLPFC). Magnitude of discounting was correlated with activity in the amygdala, DLPFC, posterior cingulate cortex and PPC.


CONCLUSIONS
Our findings were consistent with a model wherein dorsal cognitive systems modulate the neural response of ventral regions. Patients addicted to MA, who strongly prefer smaller immediate over larger delayed rewards, activate the dorsal cognitive control system in order to overcome their preference. Activation of the amygdala during choice of delayed rewards was associated with a greater degree of discounting, suggesting that heavily discounting MA-dependent individuals may be more responsive to the negative salience of delayed rewards than controls.
Hoffman
William F
WF
Mental Health and Clinical Neurosciences Division P35C, Veterans Affairs Medical Center, 3710 SW US Veterans Hospital Road, Portland, OR 97239, USA. hoffmanw@ohsu.edu
Schwartz
Daniel L
DL
Huckans
Marilyn S
MS
McFarland
Bentson H
BH
Meiri
Gal
G
Stevens
Alexander A
AA
Mitchell
Suzanne H
SH
D000328:Adult; D019969:Amphetamine-Related Disorders / Q000175:diagnosis* / Q000523:psychology; D000679:Amygdala / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology; D016739:Behavior, Addictive / Q000139:chemically induced / Q000175:diagnosis* / Q000523:psychology; D002755:Choice Behavior / Q000187:drug effects / Q000502:physiology*; D003627:Data Interpretation, Statistical; D005260:Female; D006179:Gyrus Cinguli / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D010296:Parietal Lobe / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology; D017397:Prefrontal Cortex / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*