Abstract
ObjectiveLittle is known about the effects of polysubstance use and cigarette smoking on brain morphometry. This study examined neocortical brain morphometric differences between abstinent polysubstance dependent and alcohol-only dependent treatment seekers (ALC) as well as light drinking controls (CON), the associations of cigarette smoking in these polysubstance users (PSU), and morphometric relationships to cognition and inhibitory control.MethodsAll participants completed extensive neuropsychological assessments and 4 Tesla brain magnetic resonance imaging. PSU and ALC were abstinent for one month at the time of study. Parcellated morphological data (volume, surface area, thickness) were obtained with FreeSurfer methodology for the following bilateral components: dorso-prefrontal cortex (DPFC), anterior cingulate cortex (ACC), orbitofrontal cortex (OFC), and insula. Regional group differences were examined and structural data correlated with domains of cognition and inhibitory control.ResultsPSU had significantly smaller left OFC volume and surface area and trends to smaller right DPFC volume and surface area compared to CON; PSU did not differ significantly from ALC on these measures. PSU, however, had significantly thinner right ACC than ALC. Smoking PSU had significantly larger right OFC surface area than non-smoking PSU. No significant relationships between morphometry and quantity/frequency of substance use, alcohol use, or age of onset of heavy drinking were observed. PSU exhibited distinct relationships between brain structure and processing speed, cognitive efficiency, working memory and inhibitory control that were not observed in ALC or CON.ConclusionPolysubstance users have unique morphometric abnormalities and structure-function relationships when compared to individuals dependent only on alcohol and light drinking controls. Chronic cigarette smoking is associated with structural brain irregularities in polysubstance users. Further elucidation of these distinctive characteristics could help inform the development of targeted and thus potentially more effective treatments in this large but understudied population.
Highlights
Magnetic resonance imaging methods can be used to identify unique structural differences between substance dependent populations as well as behaviorally significant neurocognitive correlates
polysubstance users (PSU) had significantly smaller left orbitofrontal cortex (OFC) volume and surface area and trends to smaller right dorso-prefrontal cortex (DPFC) volume and surface area compared to CON; PSU did not differ significantly from alcohol-only dependent treatment seekers (ALC) on these measures
In previous magnetic resonance imaging based studies, we found that alcohol dependent treatment seekers with concurrent cocaine dependence had greater gross structural abnormalities than cocaine dependent individuals without alcohol dependence [8, 9]
Summary
Magnetic resonance imaging methods can be used to identify unique structural differences between substance dependent populations as well as behaviorally significant neurocognitive correlates. In previous magnetic resonance imaging based studies, we found that alcohol dependent treatment seekers with concurrent cocaine dependence had greater gross structural abnormalities (i.e., lobar tissue volumes) than cocaine dependent individuals without alcohol dependence [8, 9]. This was consistent with a study in abstinent polysubstance users (cocaine, alcohol, heroin, marijuana) that reported prefrontal cortical volume loss compared to non-drug using healthy controls (CON) [10]. Identifying and characterizing behavioral correlates of such potentially distinct morphometric abnormalities in PSU may inform more efficient substance use treatment [16, 17]
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