Delta-9-tetrahydrocannabinol, neural oscillations above 20 Hz and induced acute psychosis.
An acute challenge with delta-9-tetrahydrocannabinol (THC) can induce psychotic symptoms including delusions. High electroencephalography (EEG) frequencies, above 20 Hz, have previously been implicated in psychosis and schizophrenia. The objective of this study is to determine the effect of intravenous THC compared to placebo on high-frequency EEG. A double-blind cross-over study design was used. In the resting state, the high-beta to low-gamma magnitude (21-45 Hz) was investigated (n 13 pairs 4 THC only). Also, the event-related synchronisation (ERS) of motor-associated high gamma was studied using a self-paced button press task (n 15). In the resting state, there was a significant condition × frequency interaction (p 0.00017), consisting of a shift towards higher frequencies under THC conditions (reduced high beta 21-27 Hz and increased low gamma 27-45 Hz). There was also a condition × frequency × location interaction (p 0.006), such that the reduction in 21-27-Hz magnitude tended to be more prominent in anterior regions, whilst posterior areas tended to show greater 27-45-Hz increases. This effect was correlated with positive symptoms, as assessed on the Positive and Negative Syndrome Scale (PANSS) (r 0.429, p 0.042). In the motor task, there was a main effect of THC to increase 65-130-Hz ERS (p 0.035) over contra-lateral sensorimotor areas, which was driven by increased magnitude in the higher, 85-130-Hz band (p 0.02) and not the 65-85-Hz band. The THC-induced shift to faster gamma oscillations may represent an over-activation of the cortex, possibly related to saliency misattribution in the delusional state.