An fmri study of verbal and non-verbal working memory in addiction
Saturday, Oct 13, 2012, 2:00 PM - 3:00 PM
*M. L. FAULKNER
, D. A. LIAO
, E. C. STRAIN
, M. Z. MINTZER
, J. E. DESMOND
, C. L. MARVEL
Psychiatry and Behavioral Sci., Johns Hopkins University, Sch. of Med., Baltimore, MD;
Neurosci., Johns Hopkins Univ., Baltimore, MD
Working memory (WM) is the ability to hold and manipulate information in mind. WM deficits in addiction may contribute to one’s inability to control drug seeking urges and impulses (e.g., ruminative cravings) (Marvel et al., 2012). Neuroimaging studies have shown that during WM for verbal content, motor areas are activated in conjunction with the anterior insula, an area believed to be involved in “interoception”, or the awareness of internally generated thoughts. Together, these activations suggest that an inner speech mechanism supports WM (Marvel & Desmond, 2012). A disrupted inner speech mechanism may contribute to ruminative drug cravings. However, few studies of addiction have examined the neural correlates of verbal WM.
We used fMRI to study verbal vs non-verbal WM in 5 methadone-maintained, opioid-dependent patients and 5 healthy controls. Patients had no illicit drug use for at least 60 days and were maintained on methadone for at least 6 months prior to testing. Participants had no history of Axis I psychiatric disorders (except for their drug use) or neurological disorders.
Participants were visually presented with verbal stimuli (letters) or non-verbal stimuli (Chinese characters). In each trial, target presentation was followed by a 4-6 sec delay while participants covertly rehearsed the targets. Finally a probe item was presented, and participants indicated via button press whether the probe matched the target. A 2 (group: patients vs. controls) x 2 (trial type: verbal vs. non-verbal) mixed design ANOVA for accuracy and response times (RT) was conducted. Event-related fMRI data analysis focused on group differences during the delay phase of the task for accurate trials only.
: There were no group differences in accuracy or RT performance. There was a main effect of trial type for RT (p< .001): participants responded faster to the non-verbal condition. Imaging analysis revealed that both groups activated motor areas of WM (e.g., left inferior frontal, premotor, cerebellar regions) in the verbal relative to non-verbal conditions. Yet, in the verbal condition, patients significantly hyperactivated the left anterior insula and anterior cingulate, a region associated with attention.
These preliminary findings indicate that patients were able to engage motor-related inner speech mechanisms used in verbal WM. However, they hyperactivated brain regions believed to involve awareness of and attention to internally generated thoughts. We speculate that heightened sensitivity to internally generated thoughts, normally an integral aspect of verbal WM, may contribute to ruminative drug craving in addiction.
NIDA Grant K01 DA030442
NIDA Grant K24 DA 023186
[Authors]. [Abstract Title]. Program No. XXX.XX. 2012 Neuroscience Meeting Planner. New Orleans, LA: Society for Neuroscience, 2012. Online.
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