A controlled imaging comparison found both shared and different network changes after d-amphetamine, LSD and MDMA. Counting altered networks did not provide a simple scale of how psychologically powerful or impairing each drug was.
Avram and colleagues analyzed resting-state fMRI from a double-blind, placebo-controlled crossover trial involving 28 healthy volunteers. They examined connectivity within networks, connectivity between networks, seed-based connections and global connectivity.
These measures describe relationships among imaging signals. “Integrity” in this context means within-network connectivity; it is not a direct measure of structural brain damage or personal integrity.
All active drugs reduced within-network integrity in several networks. The amphetamine conditions affected more networks on that measure than LSD, while LSD uniquely reduced default-mode-network integrity. LSD also produced more pronounced changes on some between-network and seed-based measures.
Thus, the apparent magnitude of a drug effect depended on the connectivity metric selected. A count from one analysis could not stand in for the complete imaging profile.
The researchers compared connectivity changes with receptor-density maps. Such spatial associations can generate mechanistic hypotheses, but the maps do not constitute direct simultaneous receptor measurements in each participant.
The authors also identified potential carryover effects as a limitation. In a crossover experiment, the possibility that an earlier condition influences a later one must be considered even when sessions are separated.
The results do not validate fMRI as a test for intoxication, establish a blood concentration cutoff or quantify an individual’s driving impairment. Healthy-volunteer group patterns also require independent validation before use in a different clinical or forensic population.
The paper supports specifying which network measure changed and under which condition. It does not support interpreting every increase as improvement, every decrease as injury, or every wider pattern as greater functional impairment.
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