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. 2015 Oct 15:293:46-53.
doi: 10.1016/j.bbr.2015.07.029. Epub 2015 Jul 14.

Combined effects of marijuana and nicotine on memory performance and hippocampal volume

Francesca M Filbey  1 , Tim McQueeny  2 , Shrinath Kadamangudi  2 , Collette Bice  2 , Ariel Ketcherside  2
Affiliations

Combined effects of marijuana and nicotine on memory performance and hippocampal volume

Francesca M Filbey et al. Behav Brain Res. .

Abstract

Combined use of marijuana (MJ) and tobacco is highly prevalent in today's population. Individual use of either substance is linked to structural brain changes and altered cognitive function, especially with consistent reports of hippocampal volume deficits and poorer memory performance. However, the combined effects of MJ and tobacco on hippocampal structure and on learning and memory processes remain unknown. In this study, we examined both the individual and combined effects of MJ and tobacco on hippocampal volumes and memory performance in four groups of adults taken from two larger studies: MJ-only users (n=36), nicotine-only (Nic-only, n=19), combined marijuana and nicotine users (MJ+Nic, n=19) and non-using healthy controls (n=16). Total bilateral hippocampal volumes and memory performance (WMS-III logical memory) were compared across groups controlling for total brain size and recent alcohol use. Results found MJ and MJ+Nic groups had smaller total hippocampal volumes compared to Nic-only and controls. No significant difference between groups was found between immediate and delayed story recall. However, the controls showed a trend for larger hippocampal volumes being associated with better memory scores, while MJ+Nic users showed a unique inversion, whereby smaller hippocampal volume was associated with better memory. Overall, results suggest abnormalities in the brain-behavior relationships underlying memory processes with combined use of marijuana and nicotine use. Further research will need to address these complex interactions between MJ and nicotine.

Keywords: Cannabis; Comorbid substance use; Hippocampus; Morphometry; Nicotine.

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Conflict of interest statement

Conflicts of interest statement: The authors report no conflicts of interest.

Figures

Figure 1
Figure 1
Hippocampal volumes normalized as a ratio to total brain volume (TBV) expressed as a z-score by group (error bars are +2 standard error).
Figure 2
Figure 2
Bivariate scatterplots with fit lines by group for hippocampal volumes (as TBV ratio z-score) with WMS-III logical memory (a) immediate recall scaled score (b) and delayed recall scaled score.
Figure 3
Figure 3
Decomposing the interaction between hippocampal volumes (as TBV ratio z- score) and nicotine use intensity (cigarettes/day) predicting logical memory immediate recall scaled scores.
See this image and copyright information in PMC

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