Luxembourg/Chicago, 08 May 2014. Neuroscientists from the Centre Hospitalier de Luxembourg and theUniversity of Luxembourg as well as Rush University Medical Center in Chicago (USA) have successfully, for the first time ever, identified part of the nerve pathways responsible for the visual disorders frequently observed in patients with Parkinson's disease. Their innovative approach "Blind to blindsight” was published in the current issue of the specialised journal “Brain”.
“Blindsight” is a strange phenomenon, observed in blind people whose visual cortex regions in the brain have been damaged. Given that some neural pathways still function well, people who are cortically blind are still able to react to certain visual information, even though this information cannot be transmitted to the upper brain centres devoted to vision.
To explain this phenomenon, it is assumed that a small amount of visual information is nevertheless unknowingly transmitted through other specific visual pathways. Thanks to blindsight, blind people can subconsciously locate a light source, unconsciously turn their eyes in the right direction and guess emotional facial expressions, such as danger or anger. All humans have this system which allows us, almost as a reflex, to react quickly and unconsciously to visual stimulations.
Researchers grouped around Dr Nico Diederich have now discovered that many of the visual disorders observed in patients with Parkinson's disease work in the opposite direction: these patients have normal vision, however they have slower eye movements and difficulty tracking objects that move. Furthermore, these patients have decreased contrast sensitivity as well as a reduced ability to analyse emotional expressions on the face of someone right in front of them. In short, these patients are “blind to blindsight”.
Using this new explanatory model, researchers have gained knowledge about the cerebral regions responsible for these visual disorders. Some have many Lewy bodies, cellular inclusions that are typical of the disease. They have shown for the first time ever that these disorders are due to disturbances in these old pathways from an “evolution” point of view.
One third of more than 5 million Parkinson's patients worldwide suffer from visual hallucinations, in addition to the disorders that have already been mentioned above. Often, these are “passage hallucinations”, during which normal visual stimuli cause patients to experience brief furtive visions of animals or moving people. The neural pathways involved may be the same as those responsible for the visual disorders described above. Slow or inadequate reactions to moving objects are also likely to affect the driving ability of Parkinson's patients.
“We have analysed all known visual disorders and have compared them with blindsight. Based on these analyses, it has been found that the vision problems of Parkinson's patients must be due in large part to the dysfunction of these old visual pathways” explains Dr Nico J. Diederich, a neurologist at the Centre Hospitalier de Luxembourg and researcher at the “Luxembourg Centre for Systems Biomedicine” at the University of Luxembourg, and who co-authored this publication with Dr Glenn Stebbins and Dr Christopher Goetz (Rush University Medical Center) and Dr Christine Schiltz (University of Luxembourg). These researchers hope that their findings will inspire other colleagues to take a “new look” at the unconscious or automatic phenomena that are disturbed in Parkinson's disease in order to better understand the processes involved.
Original publication: Nico J Diederich, Glenn Stebbins, Christine Schiltz, Christopher Goetz (2014) Are patients with Parkinson’s disease blind to blindsight? Brain ; doi: 10.1093/brain/awu/094
Released by the University of Luxembourg and the Centre Hospitalier de Luxembourg
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