Scientists from the University of Montreal have found out how LSD (lysergic acid diethylamide) changes the brain's electrical activity. It turned out that the drug not only weakens the main rhythms but also speeds them up, and also makes signals more complex and less predictable. The work was published in the journal Communications Biology.
The study involved 17 healthy volunteers. Each underwent two scanning sessions 14 days apart: in one case they were given 75 micrograms of LSD intravenously, in the other a harmless saline solution (placebo). The participants did not know what exactly was being administered to them. About four hours after the injection, they underwent magnetoencephalography (MEG), a non-invasive procedure in which the head is placed in a helmet with sensors that pick up magnetic fields from neuron activity. The scanning was performed twice for seven minutes: first in silence with eyes closed, then while listening to ambient music.
It was traditionally believed that classical psychedelics cause desynchronization, a decrease in the coherence of brain rhythms. However, standard analysis methods can confuse the speeding up of waves with their weakening. The authors used a special mathematical approach to separate rhythmic waves and background noise. It turned out that the weakening of alpha and beta waves does indeed occur, but not as widely as older methods showed. In addition, LSD accelerated alpha waves by an average of 2 Hz and beta waves by 5 Hz. Based on frequency shifts alone, a machine learning algorithm determined with more than 82% accuracy whether a recording was made after LSD or placebo (chance level is 50%).
In addition, the drug increased the complexity of signals. Two metrics were used to assess it: Lempel-Ziv complexity (counts the number of new patterns in the signal) and Higuchi fractal dimension (shows how "rough" and self-similar the signal is at different scales). Both indicators rose noticeably, especially in the occipital regions responsible for vision. Based on these features, the algorithm distinguished the states with more than 76% accuracy.
The effects of LSD were distributed unevenly across the brain: they were stronger in areas associated with vision, hearing, language, emotions and mental imagery, but hardly affected the motor cortex, which controls movements. The weakening and speeding up of waves did not always coincide, which suggests that these are two independent processes.
The influence of music turned out to be unexpected. Initially, the scientists assumed that it would enhance the drug's effect, but preliminary data (which did not pass strict statistical testing) indicated the opposite: music rather slightly reduced the changes, possibly acting as an external support that prevents the mind from fully immersing itself in the altered state. The authors emphasize that this result requires further research with a larger sample.
Among the limitations of the work are the small number of participants (17 people) and the fact that scanning was carried out four hours after administration, when the peak effect of the drug had already passed. The scientists also note that the acceleration of rhythms may affect other measures, for example functional connectivity, a measure of how coherently different areas of the brain work together. This analysis is planned in the near future.