Recent neuroimaging studies indicate that shamanic drumming induces an altered state that is biologically distinct from both ordinary wakefulness and drug-induced psychedelic states.
Here are the key findings from interesting papers on this topic: Neurological Correlates of the Shamanic Trance which correlated with visual imagery
: A study published in Frontiers in Human Neuroscience Neural Correlates of the Shamanic State of Consciousness found that while the subjective experience of a shamanic journey often mirrors a psychedelic trip, the brain activity is unique. Practitioners showed increased gamma power during drumming, which correlated with visual imagery, and decreased neural signal diversity. and decreased neural signal diversity.