Hippocampal gray matter volume in young adulthood varies with adolescent alcohol use
Journal article
Summary and highlights
A new study published in Experimental and Clinical Psychopharmacology reveals that alcohol use alters brain structures in adolescents. Researchers found that larger hippocampal volumes are affected by alcohol use during adolescence, while no such relationship was found for tobacco or cannabis use. This study contributes new knowledge to improve the understanding of how different types and patterns of substance use harm the adolescent brain.
Substance use among adolescents is a critical public health issue due to its potential long-term impact on both physical and mental health. Adolescence is a period of significant brain development, making it a particularly vulnerable time for the detrimental effects of harmful substances, such as alcohol.
PsyPost reports that previous research has linked substance use during adolescence to cognitive deficits, such as memory disruption, that can persist into adulthood. Nevertheless, so far most of the neuroimaging research focused only on heavy substance use, leaving a gap in the understanding of how low-dose consumption of harmful substances, such as alcohol, affect the brain.
This new study is closing this gap. Researchers investigated the relationship between trajectories of alcohol, tobacco, and cannabis use during adolescence and brain gray matter volume in young adulthood. This focus on the pattern of use over time, rather than a binary heavy-use vs. non-use approach, is novel and provides insights into how varying levels of substance use impact brain development, according to PsyPost reporting.
Understanding grey matter
Grey matter is a major component of the central nervous system. Grey matter is distinguished from white matter in that it contains numerous cell bodies and relatively few myelinated axons, while white matter contains relatively few cell bodies and is composed chiefly of long-range myelinated axons. Grey 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, according to Wikipedia. Grey matter contains most of the brain’s neuronal cell bodies. The grey matter includes regions of the brain involved in muscle control, and sensory perception such as seeing and hearing, memory, emotions, speech, decision-making, and self-control.
Study methodology
The researchers recruited 1,594 participants from the Birmingham, Alabama area as part of the Healthy Passages Study, a longitudinal investigation 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 use of alcohol, tobacco, and cannabis, and a subset of 350 participants underwent magnetic resonance imaging (MRI) to measure brain structure at approximately age 20.
The study used latent growth curve models (LGCMs) to analyze the trajectories of substance use 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 grey matter volume in various regions, including the hippocampus, amygdala, and nucleus accumbens.
Highlight findings
These findings challenge some of the existing notions about adolescent substance use and brain development.”
Eric W. Dolan, in PsyPost
The researchers found that cortical gray matter volume was not associated with trajectories of alcohol, tobacco, or cannabis use. However, a significant relationship was found between subcortical gray matter volume and alcohol use trajectories.
Greater alcohol use at age 14 was associated with larger volumes of the hippocampus on both sides of the brain. The intercept of alcohol use, which represents the level of use at age 14, had a positive correlation with hippocampal volume, indicating that early initiation of alcohol use might be linked to larger hippocampal size in young adulthood.
There was no observed relationship between the use of tobacco or cannabis and the volume of either cortical or subcortical gray matter regions.
These findings challenge some of the existing notions about adolescent substance use and brain development. While many studies have reported that heavy alcohol use is linked with reduced grey matter volume in various brain regions, this study found that even low and medium dose use of alcohol 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 could underlie some of the cognitive and emotional effects linked with alcohol use. The finding that early alcohol use is linked to larger hippocampal volumes suggests that different patterns of alcohol use may impact brain development in diverse ways. This could imply that already low and medium dose alcohol use interferes with the natural pruning process of synapses, leading to a retention of connections that would otherwise be pruned.
Why alterations in the hippocampal structure of adolescent brains are concerning
The finding that early initiation of alcohol use is linked to larger hippocampal size in young adulthood is concerning for several reasons:
- Abnormal Brain Development: During adolescence, the brain undergoes critical developmental processes, including synaptic pruning (eliminating unnecessary neural connections) and myelination (strengthening important neural pathways). Alcohol use at a young age can interfere with these processes, potentially causing the hippocampus to develop abnormally. A larger hippocampus in this context suggests that alcohol may be disrupting the natural pattern of brain maturation, leading to an atypical structural response.
- Impaired Memory and Learning: The hippocampus is central to memory formation and learning. If its growth is affected by alcohol use, the ability of young adults to form and retrieve memories may be compromised. A larger hippocampus may not function optimally if its growth is a consequence of damage or altered brain wiring caused by alcohol exposure.
- Maladaptive Stress Response: The hippocampus plays a role in regulating the body’s response to stress. Alcohol use during adolescence might impair the hippocampus’s ability to modulate stress hormones like cortisol, leading to exaggerated or dysregulated responses to stress. This could contribute to mental health issues like anxiety, depression, or heightened emotional reactivity.
- Link to Cognitive and Emotional Issues: If early alcohol use leads to abnormal hippocampal growth, it may increase the risk of long-term cognitive and emotional problems. Studies have shown that adolescents who consume alcohol are at higher risk of attention deficits, poor academic performance, and difficulties with emotional regulation, all of which could be tied to altered hippocampal function.
- Potential for Addiction Vulnerability: The hippocampus is involved in forming reward-related memories, which can influence addiction pathways. Early alcohol use may alter the development of this region, increasing the risk of addictive behaviors in adulthood due to changes in how the brain processes rewards and reinforcement.
Overall, a larger hippocampus in young adults who initiated alcohol use early suggests that alcohol may have disrupted normal brain development, leading to structural changes that could affect cognitive, emotional, and behavioral functioning.
Abstract
Adolescent substance use is linked with negative future outcomes (e.g., depression, anxiety, substance use disorder). Given that the brain undergoes significant maturation during adolescence, this developmental period may represent a time of particular vulnerability to substance use.
Neuroimaging research has largely focused on heavy or binge patterns of substance use; thus, relatively less is known about the neural impact of a broader range of adolescent substance use.
Characterizing the neural impact of a broader range of adolescent substance use may inform prevention and treatment efforts. The present study investigated relationships between adolescent substance use trajectories (i.e., alcohol, tobacco, and cannabis) and grey matter volume in young adulthood.
Substance use was assessed in 1,594 participants at ages 11, 13, 16, and 19. Following the last assessment, 320 participants completed a single magnetic resonance imaging session to assess brain grey matter volume.
Latent growth curve models were used to estimate growth parameters characterizing alcohol, tobacco, and cannabis use trajectories for each participant. These growth parameters (i.e., intercept, linear slope, and quadratic slope) were then used as predictors of grey matter volume.
The grey matter volume of the hippocampus was positively associated with age 14 alcohol use (i.e., intercept) but not other trajectories (i.e., progression or acceleration) or substances (tobacco or cannabis).
These results provide new insight into the neural impact of distinct adolescent alcohol, tobacco, and cannabis use trajectories, which may help to refine prevention and treatment efforts.