Neural correlates of the altered states of consciousness induced by acoustic rhythmic stimulation
[eng] Throughout history and across diverse cultures, sound has been a profound and persistent influence, shaping both individual experiences and collective bonds. Its role is evident in the way it has been harnessed in cultural and religious practices to achieve psychological states beyond the ordi...
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| Tipo de documento: | tese |
| Estado: | Versão publicada |
| Data de publicação: | 2024 |
| País: | España |
| Recursos: | Universidad de Barcelona |
| Repositório: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/221247 |
| Acesso em linha: | https://hdl.handle.net/2445/221247 http://hdl.handle.net/10803/694540 |
| Access Level: | Acceso aberto |
| Palavra-chave: | Neurociència cognitiva Escolta (Psicologia) Cognitive neuroscience Listening |
| Resumo: | [eng] Throughout history and across diverse cultures, sound has been a profound and persistent influence, shaping both individual experiences and collective bonds. Its role is evident in the way it has been harnessed in cultural and religious practices to achieve psychological states beyond the ordinary. To explore this in the past was one of the objectives of the ERC Artsoundscapes project in which this PhD can be framed. The project sought to investigate whether the acoustic properties of ritual sites facilitate the non-ordinary states desired in the spiritual practices performed there. Some psychological states reached by exposure to sound can be characterized as altered states of consciousness (ASCs). In particular, sound has been structured in various ways to facilitate non-ordinary experiences. One notable example is slow (i.e., around 2 Hz) and highly rhythmic patterns, which are employed across cultures to induce dissociative mental states. This includes drumming in shamanic rituals and the four-on-the-floor beats in electronic music events. The cross-cultural and cross-temporal use of sound to alter consciousness suggests that acoustic stimulation structured in specific ways can have a distinct effect on the central nervous system, explaining sound-induced ASCs. However, the precise cognitive and neural mechanisms of this phenomenon remain elusive. These types of non-ordinary experiences have not been adequately addressed in the scientific literature compared to other ASCs, such as some forms of meditative states and drug-induced ASCs. Previously, some progress has been made in understanding ASCs induced by highly metric sounds from a neuroscientific perspective. One physiological mechanism that has gained considerable attention in this field is neural entrainment, which refers to the phase synchronization of brainwaves with periodic external stimuli. However, systematic studies examining the direct relationship between neural entrainment and ASCs remain scarce. The primary goal of this doctoral thesis was to deepen our understanding of the neural mechanisms underlying ASCs induced by sound. Also, it aimed at advancing methodologies for studying states of altered phenomenology. A key focus of this research was on neural entrainment as a potential mechanism to explain how highly metric sounds contribute to proxies of these non-ordinary states. This exploration sought to expand our understanding of rituals in which sound is key, both historical and contemporary, by focusing on how sounds that are structured in specific ways may affect listeners. Additionally, it intended to provide a clearer insight into ASCs by examining non-ordinary experiences not influenced by pharmacological interventions. These interventions can bias our understanding of these experiences. ASCs are intricate and inherently subjective, posing challenges for their measurement. Traditionally, ASCs have been assessed through phenomenological experiences reported via retrospective questionnaires or cognitive tasks that provide insights into cognitive function at specific moments. In Study I, we reviewed research methodologies and identified gaps in the field of ASCs induced by sound. We also summarized the phenomenological, cognitive, and neural patterns associated with sound-induced ASCs into potential neurobiological mechanisms that might connect sound to non-ordinary experiences. Study I established the conceptual and methodological foundation for Studies II and III, which specifically examined rhythm-induced ASCs. In Studies II and III, we explored the relationship between proxies of ASCs induced by highly metric sounds and neural entrainment to these sounds. In particular, the sounds used were extracts of naturalistic electronic music in Study II and drumming in Study III. We manipulated rhythmic components of these auditory stimuli to create conditions of high and low strength of neural entrainment, which allowed us to subsequently explore whether the strength of entrainment was related to the intensity of phenomenological and cognitive characteristics related to ASCs. In Study II, we manipulated the strength of entrainment by varying the tempo of electronic music based on findings that entrainment to auditory stimuli reaches a maximum at rates around 2 Hz. In Study III, we manipulated entrainment by modulating the rhythmicity of drumming. To gain a comprehensive understanding of ASCs, non-ordinary states were measured by a combination of phenomenological and cognitive measures. Although neural entrainment typically refers to the synchronization in phase of neural activity with repetitive external stimuli, previous research has employed a frequency-tagging approach with electroencephalography to measure entrainment in a broad manner. Therefore, in Study II and Study III, we used a combination of frequency-tagging and electroencephalography to explore neural entrainment. Overall, this doctoral thesis reveals that highly metric and continuous auditory stimuli can induce characteristics of ASCs, including absorption, relaxation, pseudo-hallucinations, and vivid imagery. These states align with neurophysiological mechanisms involving the thalamus, thalamocortical interactions, and the default mode network, like those in psychotic and psychedelic experiences. When focusing on highly metric sounds, the rhythmic elements of these sounds enhance the subjective experience of dissolving psychological boundaries, consistent with 8 anthropological evidence that sound alone can induce ASCs in rituals. Additionally, personality traits, particularly absorption, significantly influence the phenomenological aspects of these states. High-absorption individuals reported greater disembodiment, while those with lower absorption experienced enhanced spiritual effects. Our findings also suggest that neural entrainment to highly metric sounds modulates cognitive functions related to ASCs, such as executive function and auditory sensitivity. This highlights the intricate role of both neural entrainment and personality traits in shaping sound-induced ASCs. In summary, this doctoral thesis advances our understanding of how sound induces ASCs. It highlights the role of neural entrainment, personality traits, and specific rhythmic elements in shaping ASCs induced by highly metric sounds. By integrating phenomenological, cognitive, and neural insights, this research offers a comprehensive view of the complex interplay between sound and ASCs, contributing valuable knowledge to both scientific and cultural perspectives on altered mental states. |
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