For thousands of years, humans have used drum rhythms in rituals, ceremonies, and practices designed to induce altered states of consciousness. Yet what exactly happens in the brain under the influence of repetitive sound—and why do some individuals experience profound shifts in perception while others feel almost nothing?
Researchers at the University of Barcelona sought to investigate this phenomenon within a controlled laboratory environment. The study involved 27 volunteers who had no prior history of significant dissociative states. For twelve minutes, participants listened to either steady, rhythmic drumbeats or non-rhythmic sound sequences. During this time, their brain activity was recorded using electroencephalography (EEG), while changes in their subjective experiences were evaluated through specialized questionnaires.
The results, published in the journal Annals of the New York Academy of Sciences, revealed that rhythmic stimulation enhanced feelings of unity and connectedness compared to chaotic sounds. This effect was particularly pronounced in individuals with high "trait absorption"—a predisposition for total immersion in internal sensations, music, or mental imagery. Such participants more frequently reported sensations of altered body perception, the transcendence of the traditional boundaries of the "self," and spiritual experiences.
Interestingly, while drum rhythms did increase the synchronization of brain activity, the degree of this synchronization did not directly correlate with the depth of the subjective experience. In other words, the brain might "lock on" to an external rhythm, but this entrainment does not automatically trigger a transition into an unusual state of consciousness.
The study’s authors—Raquel Aparicio-Terrés, Samantha López-Mochales, Margarita Díaz-Andreu, and Carles Escera—highlight the vital importance of individual differences. While rhythm can establish the necessary conditions for altered perception, personal predisposition and the capacity for absorption play a key role.
From the perspective of predictive processing theory, a repetitive rhythm may reduce temporal uncertainty, making it easier for the brain to anticipate the next signal and integrate sensory streams. However, the findings indicate that consciousness is shaped by more than just neural synchronization alone. It is also heavily influenced by "top-down" processing, such as expectations, attention, past experiences, and personality traits.
This can be compared to musicians performing in an orchestra. While a shared rhythm helps everyone play in unison, only those who are fully immersed in the music experience that moment where the divide between the performer and the melody vanishes.
The research demonstrates that altered states of consciousness can be triggered not only by meditation or substances but also through simple external structures like sound, repetition, and rhythm. It reveals that our brains are remarkably sensitive to the temporal patterns found in the world around us.
Nevertheless, the study does have its limitations, as the sample size was small and long-term effects were not investigated. Further research is necessary to uncover how rhythms interact with the brain and why a drumbeat remains just a sound for some, yet serves as a gateway to an altered reality for others.
