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A new Australian study finds that the visual hallucinations are experienced by patients with macular degeneration (MD) may be linked to abnormally heightened activity in the visual cortex of the brain.
Macular degeneration is a retinal eye disease that causes progressive deterioration of the central region of the retina, leading to visual loss in the field of vision, while peripheral vision usually remains unaffected. MD is a leading cause of legal blindness in people over the age of 40.
Curiously, many MDs have been diagnosed with Charles Bonnet Syndrome, in which they experience hallucinations and the brain adjusts to significant vision loss. These hallucinations can manifest as simple geometric patterns or more complex scenes involving animals, people and places.
Some patients experience hallucinations while others do not remain unclear, but it has been suggested that the activity levels, or excitability, of certain visual regions of the brain may play a role.
In the new study, a research team from the University of Queensland's Brain Institute and the School of Psychology has shown that it can significantly increase the number of patients in the visual system.
The researchers used electroencephalography (EEG) to measure brain electrical activity in three groups: a group with macular degeneration and Charles Bonnet hallucinations, a group with macular degeneration and no hallucinations, and a control group of visually-healthy elderly people.
The participants were asked to look at their numbers on the screen while they were on the screen. The checkerboards produced unusual oscillations in visual areas of the brain that could be measured using mathematical techniques.
"Said first hallucinations," it is a huge visual response compared with participants who have the same visual loss but do not have the hallucinations, "said first author Dr. David Painter.
Painter noted that while MD patients who experience hallucinations have been shown to be hyperexcitable, the translation of this hyperexcitability into hallucinations was not automatic.
"During the testing, none of our participants experienced hallucinations, so it's not that heightened excitability of the brain produces hallucinations – it's some other factor," Painter said.
"Sometimes people have these hallucinations when they are in periods of low sensory stimulation, such as in low-light or periods of inactivity, but they can be triggered by such things as wrinkles or television – it varies for the individual. "
"What we are saying is that the reports of those reporting hallucinations are more excitable, but it still remains unclear how that excitability is being translated into hallucinations – that's a question for future research."
The findings could help reduce misdiagnosis of hallucinations in people with MD.
"When they get older and they start having these unusual experiences, they are often worried about something like that," he said. .
"Doctors sometimes do not recognize the disease, Charles Bonnet Syndrome by their brain excitability in response to flickering stimuli.
The findings are published in the journal Current Biology.
Source: University of Queensland
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