Ayahuasca Research



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Study 2.

Effects Of Ayahuasca On Binocular Rivalry With Dichoptic Stimulus Alternation

Ede Frecska, Keith D. White and Luis E. Luna

One variant of stimulus presentation in binocular rivalry experiments is dichoptic stimulus alternation (DSA). In studies using DSA, stimuli are applied to the eyes in rapid alterations instead of keeping the stimulus presented to each eye constant, as in the classical paradigm (see previous study). Dichoptic stimulus alternation at frequencies much higher than the natural frequency of binocular rivalry can unveil underlying neuronal mechanisms of visual function.

This study was undertaken to investigate whether binocular rivalry survives high rates of DSA induced by ayahuasca. Individuals who were participating in ayahuasca ceremonials were requested to volunteer for binocular rivalry tests (DSA=0, 3.75, 7.5, 15 and 30 Hz) without and after drinking the brew.

Results indicated that ingestion of ayahuasca increased mean dominance periods both in standard binocular rivalry conditions (no DSA) and tests with DSA. At higher DSA rates (15 and 30 Hz) the total length of dominance periods was longer on ayahuasca.

Figure 1. Typical patterns of perceptual alternation in binocular rivalry at different DSA rates without ayahuasca

Figure 2. Typical patterns of perceptual alternation in binocular rivalry at different DSA rates with ayahuasca

From these results we conclude that ayahuasca induces changes of gamma oscillations in the visual pathways. Gamma (20-70 Hz) brain wave oscillations are prominent in the active brain. They represent a widely studied band of EEG frequencies co-occurring with information acquisition and are associated with various behavioral functions ranging from sensory binding to memory. Neurons which oscillate together (within 1 msec precision), work together regardless how far they are from each other in the brain. Gamma oscillation can be conceptualized as the clock speed of the group of synchronized neurons which are processing the same task: for example, binding several sensory inputs (visual, auditory etc.) into one subjective percept or performing memory tasks. Gamma synchronization has a potential to explain some experiences of altered states of consciousness. For example synesthesia, such as hearing a “brown” sound, can come from synchronized activity of some visual and auditory neurons. This kind of problem we have been addressing from a more direct approach in Study 5.