A recent study published in Experimental and clinical psychopharmacology Researchers have discovered a surprising link between adolescent alcohol use and brain structure. They found that larger hippocampal volumes were associated with adolescent alcohol use, while no such relationship was found for tobacco or cannabis use. This study adds new dimensions to our understanding of how different patterns of substance use affect the adolescent brain.
Substance use among adolescents is a major public health problem because of its potential long-term impacts on physical and mental health. Adolescence is a period of significant brain development, making it a particularly vulnerable period to the potentially adverse effects of substance use.
Previous research has linked adolescent substance use to cognitive deficits, such as memory impairment and impulsivity, that can persist into adulthood. Despite this, much of the existing neuroimaging research has focused on heavy substance use, leaving a gap in our understanding of how more typical and recreational levels of use affect the brain.
The present study aimed to fill this gap by examining the relationship between trajectories of alcohol, tobacco, and cannabis use during adolescence and brain gray matter volume in early adulthood. This approach focusing on the pattern of use over time, rather than a binary heavy use/nonuse approach, is novel and provides insight into how different levels of substance use affect brain development.
Gray matter is a key component of the central nervous system, consisting primarily of neuronal cell bodies, dendrites, and unmyelinated axons. It is essential for information processing in the brain and spinal cord, enabling functions such as muscle control, sensory perception, memory, emotion, and decision making. Gray matter forms the outer layer of the brain, known as the cerebral cortex, and is also found in various subcortical structures, contributing to the brain’s ability to interpret and respond to a wide range of stimuli.
The researchers recruited 1,594 participants from the Birmingham, Alabama, area as part of the Healthy Passages study, a longitudinal survey of adolescent health. Participants were initially recruited from fifth-grade classrooms and followed up at ages 11, 13, 16, and 19. At each time point, participants reported their alcohol, tobacco, and cannabis use, and a subset of 350 participants underwent magnetic resonance imaging (MRI) to measure brain structure around age 20.
The study used latent growth curve models (LGCM) to analyze substance use trajectories over time, estimating the initial level of use at age 14, the linear progression of use, and the acceleration or deceleration of use. These trajectories were then used to predict brain gray matter volume in various regions, including the hippocampus, amygdala, and nucleus accumbens.
The researchers found that cortical gray matter volume was not associated with alcohol, tobacco, or cannabis use trajectories. However, a significant relationship was found between subcortical gray matter volume and alcohol use trajectories.
Higher alcohol consumption at age 14 was associated with larger hippocampal volumes on both sides of the brain. The alcohol consumption intercept, which represents the level of consumption at age 14, was positively correlated with hippocampal volume, indicating that early initiation of alcohol consumption may be related to larger hippocampal size in early adulthood.
No relationship was observed between tobacco or cannabis use and the volume of cortical or subcortical gray matter regions.
These findings challenge some of the conventional wisdom about adolescent substance use and brain development. While many studies have reported that heavy drinking is associated with reduced gray matter volume in various brain regions, this study found that even typical recreational alcohol use during adolescence is linked to larger hippocampal volumes.
The hippocampus plays a key role in memory formation and emotional regulation, and changes in its structure may underlie some of the cognitive and emotional effects associated with alcohol consumption. The finding that early alcohol consumption is linked to larger hippocampal volumes suggests that different patterns of alcohol consumption may impact brain development in different ways. This could imply that light or recreational drinking interferes with the natural process of synapse pruning, leading to the retention of connections that would otherwise be pruned.
Furthermore, the lack of significant results regarding tobacco and cannabis use suggests that these substances may have less impact on brain structure than alcohol, or that the consumption patterns in the population studied were not sufficient to detect changes.
The findings highlight the importance of considering different patterns of substance use and their specific impacts on brain development. Future research should continue to explore these relationships, particularly with larger samples and more diverse populations. Longitudinal neuroimaging studies that track brain changes over time in relation to substance use are essential to understanding the causal pathways involved.
“These findings suggest that certain trajectories of alcohol use (i.e., early initiation) may be the most important patterns to address through population-level prevention and intervention programs, given their relationship to brain structure,” the researchers concluded.
“These findings provide new insights into the neural impact of recreational levels of alcohol consumption in adolescents, given that previous neuroimaging research has focused primarily on binge drinking. Thus, the findings of the current study can inform prevention efforts by highlighting the trajectories of alcohol use that are most likely to be associated with changes in brain structure. This new knowledge can help promote efficient use of resources and target the most harmful patterns of substance use at the population level.”
The study, “Hippocampal Gray Matter Volume in Young Adults Varies with Adolescent Alcohol Use,” was authored by Juliann B. Purcell, Nathaniel G. Harnett, Sylvie Mrug, Marc N. Elliott, Susan Tortolero Emery, Mark A. Schuster, and David C. Knight.
