Growing concerns about the impact of cannabis on developing brains have prompted new research into the cellular mechanisms behind cognitive impairment [[1]].A new study published in *Nature Communications* pinpoints a key role for astrocytes – brain cells traditionally considered merely supportive – in mediating the effects of THC on learning and memory. The findings, stemming from research led by Dr. Marta Navarrete, could offer targets for future interventions aimed at mitigating the risks of adolescent cannabis use, a period when the brain is particularly vulnerable [[2]].
Growing evidence suggests that cannabis use can impair memory, but the extent of that impairment depends on factors like frequency of use and age of initiation. Understanding how cannabis affects the brain is a crucial public health concern, especially as rates of use continue to be monitored.
A new study led by Dr. Marta Navarrete at the Cajal-CSIC Neuroscience Center in Spain, published in the journal Nature Communications, sheds light on the cellular mechanisms behind cannabis-related memory and learning problems, particularly when use begins during adolescence. The research focuses on a type of brain cell called astrocytes, traditionally considered support cells for neurons.
Researchers found that tetrahydrocannabinol (THC), the primary psychoactive component of cannabis, overstimulates astrocytes, disrupting communication between brain regions involved in learning. This overstimulation appears to be a key factor in the cognitive deficits observed in adolescent cannabis users.
In animal models, reducing this astrocyte overstimulation prevented the development of cognitive impairments, and even allowed for some recovery of lost function. While these results come from studies on mice, they highlight the particular vulnerability of the adolescent brain to cannabinoids.
The adolescent brain is undergoing significant reorganization, with regions like the hippocampus (involved in memory) and the nucleus accumbens (related to pleasure, motivation, and reward) still maturing. This period also coincides with the highest rates of cannabis use, particularly in Western countries.
Recent data from Spain’s 2025 “Estudes” survey, published by the Ministry of Health, indicates a 5.9 percentage point decrease in the percentage of students aged 14-18 who have ever tried cannabis, down to 21% compared to 2023. However, cannabis remains the most prevalent illicit substance used by students in this age group. The survey found that 21.0% of students reported ever having used cannabis, 15.5% in the last 12 months, and 11.6% in the last 30 days. The average age of first use is 14.8 years.
These findings contrast with data from a separate Ministry of Health report, “Informe Edades 2024,” which shows that 43.7% of individuals aged 15-64 have used cannabis at some point in their lives (compared to 40.9% in 2022). The average age of first use in this older population is slightly above 18, and 2.8% reported daily cannabis use in the last month.
Previous research has established a link between THC and memory and learning deficits, but the specific cellular mechanisms remained unclear. Dr. Navarrete’s team identified a specific group of astrocytes, known as an astrocyte ensemble, as playing a critical role in these cognitive effects.
Astrocytes, once viewed solely as support cells, are now recognized as active participants in brain function. They communicate with neurons and regulate processes essential for synaptic transmission. Each astrocyte can form up to two million connections in the human brain, demonstrating their complexity.
“This study reaffirms the central role of astrocytes in brain function, demonstrating that their involvement is crucial,” the researchers stated. “Specifically, we show that altering these cells is sufficient to cause the cognitive deficits that appear after exposure to THC during adolescence.”
The study involved monitoring how THC alters astrocyte activity in the nucleus accumbens, a key region of the brain’s reward circuit. Adolescent mice exposed to THC performed significantly worse on a spatial learning task, exhibiting more errors than control groups. Spatial learning relies on coordinated activity between the hippocampus and the nucleus accumbens.
Building on previous work showing that astrocytes form specialized functional groups, the researchers investigated the specific astrocyte ensemble involved in this learning circuit. They utilized AstroLight, an innovative technique that uses light to convert astrocyte calcium activity into protein expression. This allowed them to precisely manipulate astrocyte function, either increasing or decreasing activity.
Using AstroLight, the team identified the astrocyte ensemble involved in spatial learning and modulated its activity during or after THC exposure. They found that reducing the activity of this specific astrocyte subset prevented cognitive deficits, while activating it after THC treatment improved spatial learning. “These results underscore the essential role this astrocyte ensemble plays in the effects of the psychoactive substance in cannabis during adolescence,” explained Cristina Martín-Monteagudo.
These findings offer a new perspective on the effects of cannabis during critical stages of brain development and could pave the way for more targeted interventions in the future. “Our data indicate that manipulating these astrocytes directly changes how the brain responds to cannabis during adolescence, and provides a clear map of which cells we need to study to understand and mitigate the effects of these substances at vulnerable ages,” researchers noted.
“This work reminds us that brain development is not a uniform process and that there are windows of particular vulnerability,” added Martín-Monteagudo. “This research is an important step towards protecting mental and cognitive health during adolescence.” The study was a collaborative effort involving researchers from the University of California, Los Angeles (UCLA), the Achucarro Basque Center for Neuroscience, and the Neurocentre Magendie at the University of Bordeaux, highlighting the importance of international cooperation in neuroscience research.
