A recent study published in Neuropsychopharmacology investigates the acute effects of different types of cannabis on resting-state brain networks in young adults and adolescents. The research focuses particularly on the impact of the two predominant phytocannabinoids in cannabis—Delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD)—and their influence on brain connectivity.

Background and Motivation

Adolescence is a period of rapid neurodevelopment, making the endocannabinoid system particularly susceptible to changes. With the increasing prevalence of cannabis use among adolescents, understanding its effects on the developing brain is crucial. This study aimed to explore if adolescents are more or less vulnerable to cannabis’s impact on brain-network connectivity compared to young adults and whether CBD can mitigate THC’s effects.

Study Design and Participants

The study involved 46 semi-regular cannabis users, divided into two groups:

• Adolescents: 22 participants aged 16-17 years.
• Young Adults: 24 participants aged 26-29 years.

Both groups were matched for cannabis use frequency, which ranged between 0.5 and 3 days per week. Participants underwent fMRI scans to examine resting-state brain activity after inhaling vaporised cannabis.

Cannabis Administration and fMRI Scanning

Types of Cannabis Used

Participants were administered three types of cannabis in a randomised, double-blind, placebo-controlled design:

• Placebo: 0 mg THC, 0 mg CBD.
• THC-only: 8 mg THC per 75 kg body weight.
• THC + CBD: 8 mg THC and 24 mg CBD per 75 kg body weight.

Methodology

Cannabis was administered using a Volcano Medic Vaporizer to ensure precise dosing. Resting-state functional magnetic resonance imaging (fMRI) scans were conducted approximately 50 minutes post-inhalation to capture peak drug effects. Resting-state fMRI measures brain activity by detecting changes associated with blood flow while the participant is not performing any specific tasks.

Key Findings

The study revealed significant reductions in within-network connectivity across several key brain networks when participants were under the influence of cannabis compared to placebo:

Network Connectivity Disruptions

• Default Mode Network: F[2,88] = 3.97, P = 0.022, η² = 0.018
• Executive Control Network: F[2,88] = 18.62, P < 0.001, η² = 0.123
• Salience Network: F[2,88] = 12.12, P < 0.001, η² = 0.076
• Hippocampal Network: F[2,88] = 14.65, P < 0.001, η² = 0.087
• Limbic Striatal Network: F[2,88] = 16.19, P < 0.001, η² = 0.102

Whole-Brain Analysis

Whole-brain analysis showed significant disruptions in functional connectivity with cortical regions, as well as the executive control, salience, hippocampal, and limbic striatal networks compared to placebo.

Role of CBD

Contrary to common assumptions, CBD did not counteract THC’s disruptive effects. In some cases, CBD even potentiated the effects, further reducing connectivity both within networks and across the whole brain.

Age-Related Differences

The study observed age-related differences but found no interactions between age group and cannabis treatment in any brain network. This indicates that cannabis causes similar disruption to resting-state connectivity in both adolescent and adult brains.

Source: Nature