Multimodal Ganzfeld-induced visual experiences are associated with alongside mental experiences and distinct EEG microstate dynamics

Our minds are constantly at work, weaving together the sights, sounds, and sensations of the world into a coherent story. We see a tree, hear a bird, and our brain instantly organizes these inputs into a stable picture of reality. This process relies on a steady stream of information from our senses. But what happens when that stream stops? When the world around us becomes a blur of unchanging light and sound, the brain does not simply shut down. Instead, it begins to generate its own images and sounds, creating a vivid inner world that feels as real as the one outside. This phenomenon, where the mind fills in the void left by a lack of sensory input, offers a rare window into how our brains construct reality and how they might sometimes lose that grip, leading to experiences that others might call hallucinations.

A team of researchers set out to understand exactly what is happening inside the mind and brain during these moments of sensory deprivation. They invited people into a quiet room filled with a uniform, unstructured field of light and sound, a setup known as a Ganzfeld. In this environment, the usual sharp edges of the world dissolve into a soft, featureless haze. While sitting in this state, the participants were asked to pause and report what they were seeing and thinking. They described the complexity of the visual shapes appearing before their eyes and noted whether their minds were focused on predicting what might happen next, noticing when their expectations did not match reality, or simply drifting through old memories. At the same time, the researchers recorded the electrical activity of the participants' brains, tracking how different large-scale networks of neurons fired in rapid, shifting patterns over time.

The study revealed that as the visual experiences became more complex and detailed, the participants' thoughts also changed in specific ways. These mental shifts were not random; they were tightly linked to four distinct types of thinking: beliefs about what was being perceived, the struggle to predict the next moment, the active effort to update those predictions when they failed, and the presence of unrelated thoughts from the past. The researchers found that the brain's electrical activity reflected these changes with remarkable precision. When the inner visuals were simple, the brain operated in one pattern. When the visuals grew complex and the thoughts became more intricate, the brain switched to a different, often nonlinear, rhythm. These shifts involved networks responsible for processing sight, detecting what is important, and turning attention inward.

The findings suggest that the brain does not passively wait for the world to speak to it; it actively constructs reality based on a constant dialogue between expectation and sensory input. When the sensory input is removed, the brain's internal machinery becomes the primary driver of experience, and the way it organizes these internal events follows a distinct, measurable path. This work indicates that the Ganzfeld method provides a valuable model for studying how the brain generates experiences, offering a clearer view of the mechanisms that might go awry in conditions where people perceive things that are not there, such as in certain forms of psychosis. By mapping the connection between what we see in our minds and how our brains fire, the study helps clarify the delicate balance that keeps our perception of the world stable and real.