Neuroscientists gain insights into blindsight

Nadja Geipert NEUROSCIENTISTS using transcranial magnetic stimulation to induce temporary blindness report that healthy volunteers are still able to sense colour and orientation of visual stimuli through a secondary unconscious visual pathway. The study answers the thirty- year old question whether this phenomena, called blindsight – first observed several decades ago in legally blind patients due to primary visual cortex damage – exists in healthy humans. The researchers used Tony Ro transcranial magnetic stimulation (TMS) to induce very short-term projected from the retina to blindness in four healthy women visual cortex, he explained. and two men.The first step was to use TMS to localise the Blinded subjects discriminate primary visual cortex and colour and orientation of Ro PhD, photo by Jeff Fitlow Courtesy of Tony determine the stimulation visual stimuli By placing a transcranial magnetic stimulation coil over the visual cortex of the brain, a brief period of blindness was induced in sighted individuals. Nonetheless, it was intensity needed for disruption. shown that both colour and orientation can be processed unconsciously without primary visual cortex, a phenomenon being referred to as blindsight. Then the scientists presented the When asked what they had seen, study participants with either the volunteers responded that “blinded” volunteers’ performance As a last step, the investigators demonstrate some ability to green or red dots while they couldn’t see anything. But was well above chance. asked the study participants to respond to visual stimuli even “blinding” them briefly with TMS. when forced to choose between a “We showed that people can rate how confident they felt though they can no longer “see”. They did a similar experiment vertical and horizontal line or a discriminate colour and about their guesses on a scale Until now it was unclear with six different volunteers, this green and red dot, the participants orientation of visual stimuli at from 1 to 10.When they rated whether this secondary pathway time using vertical or horizontal guessed correctly 75% of the time highly accurate levels without any themselves more confident about also functions in healthy subjects lines. when it came to the stimulus’ conscious awareness and while their guesses, they also were with an intact visual cortex, and The stimulation with TMS, orientation and 81% of the time their primary visual cortex was more accurate. But still, even the many researchers hypothesised which lasts only 60-100 when guessing the stimulus’ disrupted, ” said Tony Ro PhD, participants who rated their that the secondary pathway, milliseconds over visual cortex, colour. One person even guessed associate professor of psychology confidence low guessed which most likely runs from the has to occur after presenting the the colour of the visual stimulus at Rice University in Houston, accurately much more often than retina to the superior colliculus visual stimulus to effectively correctly every time. Statistical Texas and the study’s lead they estimated, which suggests directly to the extrastriate interrupt the information being analysis confirmed that the investigator. the subjects had processed more cortex, only strengthens when information than they were people suffer from primary visual aware of. cortex damage. “There is a dissociation between what people know Expanding applications about their performance and “We will learn their actual performance,” said Dr Ro. more about how for TMS In the cases of higher confidence ratings, the subjects the visual brain is recently become advanced sad face.The face appeared might have been unaware of their enough for the stimulation of either to the left or the right of knowledge, but the unconscious organised through very specific brain regions. It is a fixation dot, and the study processing probably still affected currently used in some countries participants had to report on their sense of their own this kind of work,” for the treatment of depression. both the location and the performance, according to Dr Sabine Kastner PhD Some optimists even see emotional expression of the Ro. “If you would have asked me, if potential for future use in the face.When activity in the striate Most importantly however, the the secondary pathway functions treatment of schizophrenia, cortex was disrupted, they findings indicate that the brain in healthy people, I would have Parkinson’s disease and epilepsy. couldn’t localise the faces but has an alternate visual pathway said no way.We will learn more Jacob Jolij A second experiment also they still guessed the faces’ that bypasses the primary visual about how the visual brain is published in the Proceedings of emotion well above chance level. cortex and allows for the organised through this kind of Transcranial magnetic stimulation the National Academy of “I think our studies firmly “correct” processing of visual work,” said Sabine Kastner MD involves using a large coil placed Sciences just a few weeks before establish TMS as an important information without PhD, associate professor of on a subject’s skull that produces Dr Ro’s research used TMS tool in the study of blindsight consciousness. psychology at Princeton a magnetic field that can successfully to induce affective and visual awareness, and University, New Jersey. penetrate a few centimetres blindness— the ability to detect convincingly show that blindsight Secondary pathway of visual This research provides first deep and induce electrical signals the emotional expression of a can be induced in normal processing evidence that the secondary in the brain.As a result, the face without seeing it. observers,” Jacob Jolij, PhD, a Vision researchers have known pathway for visual processing is brain’s regular biochemical “It shows that we process postdoctoral fellow at the Swiss for some time that the pathway functional, she emphasised. activities are disrupted. emotional information outside of Federal Institute of Technology in for conscious processing of visual “The secondary pathways are Aside from its ability to induce visual awareness,“said Dr Sabine Lausanne, told EuroTimes. information runs from the retina used almost for sure. If they temporary blindness,TMS has Kastner. to a sub-cortical structure, the were recruited later, then you [email protected] many other applications. It can In the experiment, ten thalamus, and then to the visual would not be able to show it on also deactivate other parts of neurologically normal volunteers cortex.They have also long this kind of short-term basis the brain for investigation.The were presented with schematic believed that there is a with TMS.The experiment technology has been around for faces or emoticons that secondary pathway that springs delivers strong evidence that more than 20 years but has only expressed a neutral, a happy or a to action when patients with they are being used and that they visual cortex damage have some function.”

EuroTimes March 2006 Thirty years ago, Lawrence functionally and physiological “We think these alternative damage or Riddoch syndrome in scanner to activate the pathways Weiskrantz and colleagues at separate pathways.The first, routes are there for coarse which patients can only perceive and determine their specific Oxford University first observed conscious pathway runs from the coding of visual information; visual stimuli in motion. Maybe function, according to Dr blindsight in a patient with retina through the lateral these pathways allow us to react such patients could be trained Kastner. cortical blindness due to primary geniculate nucleus in the quickly without extensive through visual test trials “I think it’s one of these visual cortex lesions. thalamus terminating in the processing.” combined with feedback on their findings that will spark more Weiskrantz discovered that primary visual cortex.A second, studies along those lines,” she even though the subject unconscious, pathway runs from added. performed like a blind person on the retina through the superior The discovery of blindsight contributed visual performance tasks, when colliculus in the midbrain to the The study appeared in the journal he forced the subject to make a motor areas of the brain stem. to the popular neurological idea that Proceeding of the National Academies of decision about a visual stimulus, The current study used Science (PNAS, November 15, 2005 vol. the patient performed at a 70% colours and orientation, which 102 no. 46 16875–16879). performance level – well above can’t be processed very visual processing occurs in two chance. Since that initial effectively in those brain regions Tony Ro PhD observation, this forced-choice of the midbrain and indicates functionally and physiological separate [email protected] paradigm, which was also used in that there is a pathway that Sabine Kastner PhD the above experiment, was bypasses the normal primary pathways. [email protected] tested on many other subjects processing hierarchy, with direct with similar lesions and usually thalamic projections to the led to the same findings. extrastriate cortex. While blindsight is a rare performance to trust their The discovery of blindsight Secondary pathways might phenomenon, Dr Ro still thinks unconscious visual instincts. contributed to the popular make sense from an evolutionary his research might have future In the meantime, the next step neurological idea that visual standpoint, noted Dr Ro. clinical applications for patients should be a similar experiment processing occurs in two with primary visual cortex like Dr Ro’s done in an fMRI Europe’s ophthalmologists more united than divided on key issues Dermot McGrath list for cataract removal was rising surgeons (95%) said their cataract The same conservative Heidelberg, Germany.A survey, in Lisbon but in 2002 the government gave procedures were sutureless. approach also holds true for highlighting key issues in refractive a two-month waiting list surgical technique, said Dr Henry, surgery such as the type of THEY might speak different guarantee, which meant that Dutch surgery rates with monomanual phaco used by technology used, prices charged languages but when it comes to patients were less inclined to increasing over 80% of surgeons, compared and procedure volumes problems of rising costs, tighter spend their own money to have In his annual survey of the to bimanual at 15%. performed, was sent to 267 margins and coping with ever- the surgery performed,” he said. practice styles and preferences of Dutch surgeons are almost German refractive surgeons.A higher volumes of cataract In total, Danish surgeons Dutch cataract surgeons,Ype unanimous in their preference for total of 132 (49%) surgeons patients, Europe’s performed an estimated 37,500 Henry MD said that the volume of superior incisions (91%), with replied. ophthalmologists all seem to be cataract surgeries in 2004, 99.7% cataract surgery continues to rise hardly any temporal or steepest K The more notable findings singing the same song. of which were phacoemulsification in the Netherlands. Some 286 out incisions. included the fact that more than The key issues facing the procedures, with just 0.3% using of 396 cataract surgeons who The viscoelastic of choice is 90% of respondents performed continent’s eye doctors were extracapsular extraction. In terms responded to the survey (72%) Healon (AMO) at 48%, followed LASIK surgery, 50% PRK, 43% brought into sharp focus in a of the type of anaesthesia used, reported a gradual but steady by ProVisc (Alcon) with 21%.The LASEK, and 13% Epi-LASIK. Phakic series of presentations on practice 45% preferred topical, 25% increase in the volume of patients preferred technique for IOLs and refractive lens exchange styles and trends in various intracameral, 16% peribulbar, and being treated for cataract. phacoemulsification is four- are also increasingly popular European countries during the 8% retrobulbar. quadrant divide-and-conquer for procedures, noted Dr Auffarth, XXIII Congress of the ESCRS. 80% of surgeons. with 42% of respondents In the 12th annual survey of In terms of lens choice, acrylic performing both on a regular Danish cataract surgery,Tom “In 2002 the government gave a two- is the most popular IOL material, basis. Eggert Hansen MD, Odense accounting for 75%, with a Some 77% of respondents said University Hospital, said that this month waiting list guarantee, which majority preferring hydrophobic that they used their excimer laser year’s responses highlighted some lenses. Dr Henry also noted that in private practice or a laser clinic. interesting trends. meant that patients were less inclined despite the growing range of For laser centre surgeons, 46% “There are just a little over 100 multifocal IOLs coming on stream, used the Bausch and Lomb 217 or cataract surgeons in Denmark and to spend their own money to have the more than 98% of respondents 217z laser, followed by 24% for 100 of them exactly responded said they implanted five or less the Schwind Esiris, and 12% for this year, which is a high response surgery performed,” multifocal IOLs per year. the Wavelight Allegretto. Private rate. Of those who responded, “We do a lot of cataract and it is The Dutch survey revealed practice users also preferred the 32% work in private practices and Dr Hansen reported that both increasing all the time.About 27% rates of dropped nucleus of 0.70 Bausch and Lomb 217 (34%), 68% at public hospitals.And on 12 o’ clock and oblique incisions of surgeons perform between 16 per 1,000 cases. Endophthalmitis followed by the Allegretto (33%) average we perform about 375 have their loyal advocates among to 25 cataract operations per occurred at a rate of 0.45 per and CZ Meditec Mel 80 (17%). In operations per year,” he said. Danish surgeons (34% each), month, 48% between 26 and 50 1,000 cases. university eye clinics, the Schwind Dr Hansen said that 13% of the followed by temporal (24%) and and 12% over 50 per month,” said Concerning cataract outcome Esiris is the most popular, used by cataract surgeries were paid for meridian incisions (8%).The Dr Henry,Academic Hospital Vrije data collection, 54% of cataract 37% of respondents.The most by patients themselves, while 87% preferred location for the incision University,Amsterdam,The surgeons are using a computer widely used microkeratome is the were paid for by public funds. He is 1.0mm behind the limbus for Netherlands. program to collect the data, B&L Hansatome (59%) followed noted that a government initiative 40% of respondents, while 30% Dr Henry noted that the compared to only 37% a year ago. by the AMO Amadeus (15%), he to reduce cataract waiting lists on opt for corneal incisions, and 25% approach to anaesthesia is still reported. the national health service had the prefer the limbal approach. quite conservative in Holland. Refractive surgery growing in Tom Eggert Hansen MD, effect of reducing the number of In terms of IOL use, 78% of Retrobulbar is still number one, Germany [email protected] patients willing to pay for the respondents expressed a although declining, at 51%.Topical The evolving refractive practice Ype Henry MD, FEBO operation themselves. preference for acrylic lenses, anaesthesia is becoming more trends of German [email protected] “The statistics show that in the followed by 17% for PMMA and popular and is now used by about ophthalmologists were analysed by Gerd Auffarth MD, years 1998 to 2001, the waiting just 2% for silicon.Almost all one fifth of respondents. Gerd Auffarth MD, University of [email protected]

EuroTimes March 2006