Some people have lost their eyesight, but they continue to “see” in vivid visual hallucination.
This is not a miracle but a neurological syndrome that has been known for more than 250 years considered rare but is probably much more common than previously thought.
In 1769, the Swiss scientist Charles Bonnet described how his 87-year-old grandfather had almost complete blindness but saw clearly and in detailed visions of people, animals, and buildings.
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Scientists at the Weizmann Institute of Science, led by Prof. Rafi Malach, investigated the phenomenon. Their findings, published today in the scientific journal Brain, suggest that regular, spontaneous activity in the visual centers can trigger visual hallucinations in the blind.
In fact, it is possible that many of those who have lost their sight experience this syndrome but are afraid to share it with others for fear of considered as if they lost their minds.
However, this syndrome indicates an utterly normal brain activity – and these hallucinations have no connection or affinity to any mental illness or neurological disease.
The scientists at the Weizmann Institute of Science documented the brain activity of blind people with Charles Bonnet Syndrome – and even translated their visions into videos that were later shown to people with normal vision – to understand the brain activity for this syndrome.
The findings reveal the mechanism responsible for these hallucinations’ appearance. They show that both visions derived from external sensory input and hallucination originating in the brain are related to the activity of those brain regions that create the visual experience.
Prof. Rafi Malach’s laboratory in the Department of Neurobiology is studying one of the most miraculous human brain features – our ability to behave spontaneously and creatively.
These mysterious “spontaneous resting waves”, which occur all over the brain, take place well below the consciousness threshold. Although this phenomenon, whether this brain activity is related to behavior, has been extensively studied, it is still a mystery. Their function is still largely unknown.
The Israeli research group hypothesized that spontaneous behavior is made possible by extremely slow brain activity oscillations, which occur below the threshold of consciousness.
The ability to test whether spontaneous brain activity leads to unexpected behavior is minimal for several reasons: First, it is not possible to command people to behave spontaneously, and certainly not on subjects who are inside an MRI machine.
Second, it is difficult to distinguish between brain activity that originates from environmental stimuli and spontaneous brain activity that does not arise as a result of environmental stimulation.
In a study led by Dr. Avital Hahamy, a former research student in Malach’s lab who is now a postdoctoral research fellow at University College London, the relation between these hallucinations and the spontaneous brain activity has indeed been unveiled.
Five people who lost sight but experienced clear visual hallucinations from time to time participated in the research.
These participants’ brain activity was measured using functional magnetic resonance imaging (fMRI) scanner while they described their hallucinations as these occurred. The scientists then created movies based on the participants’ verbal descriptions, and they showed these movies to a sighted control group, also inside the fMRI scanner.
A second control group consisted of blind people who had lost their sight but did not experience visual hallucinations. These asked to imagine similar visual images while in the scanner.
Visual areas of the brain activated in the three groups – the hallucinated, those that watched the films, and those creating imagery in their minds’ eye.
But the researchers noted a difference in the timing of the neural activity between these groups. As expected, in sighted and imaginative blind people, neural activity in the visual areas occurred in response to vision or the task of imagination.
In people with Charles Bonnet syndrome, something else happened: neural activity emerged just before the onset of the hallucinations.
The researchers saw how a slow wave of activity – probably a “spontaneous resting waves” – gradually rose, and only then did it hurt the minds of Charles the Builder’s visionaries.
“Our research clearly shows that the same visual system works both when we see the outside world and also when we imagine, hallucinate – and probably also dream,” says Prof. Malach. “The study illustrates the creative power of vision and the importance of spontaneous resting waves in the brain’s ability for spontaneous and creative behavior,” he said.
Aside from the importance of the scientific findings, Dr. Hakami also seeks to raise awareness of this syndrome’s existence, which is of great anxiety among those dealing with it.
“Often, people with Charles Bonnet syndrome do not tell their doctor or even their families. It is important for these people to understand that this is a completely normal phenomenon – although their eyes no longer transmit information to the brain, their brains’ visual system is typical and continues to work. These hallucinations are evidence of this.”