Researchers from the Netherlands Institute of Neuroscience have begun to unravel the mystery behind hallucinations caused by flickering lights. Specifically, they wanted to understand the hallucinations of geometric shapes first observed in 1819, when neuroscientist Jan Purkinje discovered that bright full-field light flashes could cause our brains to perceive geometric patterns and images spontaneously.
Still, while scientists have known about this phenomenon for two centuries, the study authors say this is the first work to try to unravel the exact mechanisms in the brain responsible for these non-drug-induced hallucinations.
The Difficulty of Studying Hallucinations in the Human Brain
In the press release announcing the study, the neuroscientists who conducted the experiments note that actually studying the process behind these stroboscopic-induced hallucinations is exceedingly difficult, especially in humans. According to the study’s lead author, Rasa Gulbinaite, this is due to the complex structure of our brains.
“I study brain waves, and the effect rhythmic lights, sounds, and touch have on our brain rhythms,” Gulbinaite explains. “In humans, this is difficult to measure because our brain has folds, and what happens on the bottom of the lake is not necessarily what we can measure on the surface.”
However, Gulbinaite says that mice’s brains are flat. This fundamental difference makes it easier to “map the activity on the surface.”
Experiments Show Perception of Geometric Patterns Could Be Caused by Standing Waves
To conduct their experiments, the team used genetically modified mice. Specifically, the mice were programmed with a “fluorescent label” attached to specific neurons. When these particular neurons were activated, they glowed, allowing the researchers the unique ability to observe that neural activation in real-time directly.
“When we stimulate a specific location in the visual field, we expect to see activity in the corresponding area of the visual cortex that represents this location,” Gulbinaite said.
That neural activation was also tracked with a high-speed camera that took pictures of the brain’s surface while the mice were exposed to flickering lights. Since these particular mice were genetically modified to have the neurons of their visual cortex light up in response to visual stimuli, Gulcinaite said this was “precisely what we observed.”
However, the research team also noticed something else. When the mice were shown the flickering lights, traveling waves of neural activity propagated from the initially stimulated spot “through the visual cortex.” Unlike a typical traveling wave pattern, they noticed that these waves were bouncing back on each other to cause peaks of neural activity. Scientists call these “standing waves.”
“These waves resembled the ripples created by a raindrop falling into a pond,” Gulbinaite said. “When raindrops fall at regular intervals, their ripples spread out, bounce off the banks, interfere with each other, and can create patterns similar to standing waves.”
According to the study authors, this is “exactly” what they witnessed in the mouse brain during stimulation with flickering lights. The traveling waves originating in one part of the visual cortex “transformed” into standing waves. The resulting peaks of neural activity caused by the collision of these traveling waves meant that certain regions became more active while others became less active.
“Some parts of the pond’s surface appear still, while others oscillate with maximum amplitude,” Gulbinaite said.
Whether or not the Mice Hallucinated Geometric Patterns is Still Undetermined
In the study’s conclusion, the researchers point out that although their work confirmed the hypothesis that flickering lights can cause standing waves in the brain’s visual cortex, this does not necessarily mean that the mice in the experiment also experienced hallucinations the same way humans do.
“Whether mice also hallucinated geometric patterns, we cannot tell because we cannot ask: this is the most challenging part of our research.” Gulbinaite conceded.
Still, the study authors believe their work found good evidence that this is the case. For example, they note that when people describe their hallucinations caused by flickering lights, they often also note that the hallucinations become “finer” or more precise when the frequency of the flickering lights increases. According to Gulbinaite, “that is exactly what we also saw in the brains of mice: as the frequency increased, the patterns in the visual cortex became finer.”
The researchers note that follow-up efforts will be needed to further clarify whether the observed standing wave patterns cause hallucinations in humans. However, they believe the study’s results show they are on the right track.
“We don’t have a definitive answer yet,” Gulbinaite said, “but we are now showing convincing evidence for the first time.”
The experimental study “Spatiotemporal resonance in mouse primary visual cortex” was published in the scientific journal Current Biology.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.