- Natalie Banacos

Dr. Frank Werblin at UC Berkeley has dedicated nearly his entire academic life to the study of the eye and visual processing. More recently Dr. Werblin has completed his model of the retinal processing system he has deemed “The Retinal Hypercircuit”. The Hypercircuit itself is made up of the five classical retina cell types: Photoreceptor, Horizontal, Bipolar, Amacrine and Retinal Ganglion Cells, but more recently, a collaborative effort has identified over 50 morphologically different cell types. Of this vast array of unique cell types the most variance falls in the morphology of the Amacrine cells, which offer horizontal properties in the Inner Plexiform Layer between the Bipolar and Ganglion Cells. Although the mechanics behind the Hypercirtuit are fascinating, what I find arguably more important is the output of the system, a topic which Werblin has indirectly stumbled upon, but which I believe could potentially lead to an incredibly progressive line of research.

Amacrine Cell Types

In his studies, Werblin has stumbled upon a couple novel properties of Ganglion Cell output which may hold more information about visual processing than meets the eye. First, he has discovered that the stream of visual information to the brain is actually not a “stream” at all, rather a set of discrete pieces of information sent at different times and with different inherent signal properties. Another finding was that each of the 12 morphologically distinct Ganglion Cells processes only a certain type of stimuli. Perhaps, as an example, one type of Ganglion Cell processes the signal that “something is looming” while another “something is moving to the right”. Although this organization is indeed the work of the Hypercircuit and is mind-blowingly complex, Werblin has shown that the signal leaving the each Retinal Ganglion Cell encodes a certain stimulus quality, discrete in time and purpose. There is a problem with this theory though: We actually perceive a “stream”!

In a recent e-mail correspondence with Dr. Werblin I asked whether there were certain signals that were processed more quickly than others. If you think about it this must be true. When someone jumps out of a bush at night and scares you, you are not at first aware that the person is wearing a red coat, rather that they are there, human and dangerous! This was indeed the response I received from Dr. Werblin. He said enthusiastically, “YES SOME MORE QUICKLY THAN OTHERS” and further that they are probably organized in an evolutionarily advantageous processing order. But again, there is a problem with this, we perceive stream…And not only that but another potent flaw in this discrete logic: If we were to be a constant delay between visual cues, say, we perceive “thereness” before we perceive “color” from birth to death that delay would be constantly growing. Hypothetically, if there were a 0.001ms difference between when we perceive “shape” and “color”, for every second of life we would be adding 0.001ms to the total gap between our perception of shape and color. Visually, we could represent this as two divergent graphs, each having a slope corresponding to the rate at which we perceive that discrete visual quality. As these graphs grow over time they are divergent which means that if our system worked in this simple discrete manner then by late life we would be perceiving the shape of a stimulus, only to receive the color information a day or so later.

Divergence of Visual Stiumulus Quality Arrival Time

So, in essence, it cannot be this simple, there must be something we are missing. Sadly, no research has ever been dedicated to answering this question so for now we can only guess and I think I have a solution that works.

Remember, the visual information is discrete in time and quality. The cut of visual information from the retina to the brain, or what actually makes the signals discrete, is done by a short eye movements called a Microsaccades which occur thousands of times per second. I believe, and again this is all speculation, that these Microsaccades have developed to sync up all of our visual data from all of the different Ganglion Cells. I think that they function to hold the feed of visual information until all of the visual qualities have been analyzed by their respective locations in the brain and the proper reactions have been then initiated. Once our brain has reacted to one of these discrete packages defined by microsaccadic borders our eyes can let up, the saccade can stop, and our eyes can again be soaked in a new set of electromagnetic data for analysis. If we could further analyze which qualities are encoded and sent by the retina in what order we may be able to extract information about downstream processing or evolutionary importance, but until then this idea may have to lie in the realm of mere hypothesis.

Again, I have to stress that this is speculation based on emergent data not intended for this use, but, as a closing remark I would like to mention one thing: When I posited this idea to Dr. Werblin himself he responded with simply, “MAKES SENSE!!!”. Further, for anyone interested in the more detailed workings of the hypercircuit, on The Werblin Lab’s website, which is linked just below, there is a visual walk-through detailing the entire logic and processes behind and within it.

Werblin Retinal Hypercircuit – Werblin Lab

The mantis shrimp diverged evolutionarily from the crustacean mainline about 400 years ago and have since developed unique characteristics. Unlike most other crustaceans, they actively hunt prey and kill it with a crushing blow which has been theorized to be strong enough to create bubbles containing gas at temperatures upwards of 2000 Kelvin. This quality, however, is nowhere near as stunning as the mantis shrimp’s most incredible attribute: their eyes. In April 2001, the most comprehensive paper to date describing the mantis shrimp’s visual system was published by Justin Marshall and Thomas Cronin in The Biological Bulletin. In their paper, the authors described the unusual characteristics of the mantis shrimp visual system and hypothesized the applications of this system in the development of machine vision.

Mantis Shrimp Eye via New Scientist

The first moderately unique quality of the mantis shrimp eye is a property which arises simply from the anatomy itself. Each eye is broken up into three distinct areas: two hemispherical regions on either side of a central “midband” area. Interestingly, each ommatidium (photoreceptor) in the hemispherical regions has a corresponding ommatidium in the opposing hemisphere with which it shares a visual field. This characteristic allows for stereoscopic visual perception within each eye. In other words, each eye of the mantis shrimp has the internal ability to produce depth perception and create a three-dimensional representation of the world without input from the other eye. While the eyes of humans have to move in synchrony in order to create depth perception, the eyes of the mantis shrimp can move freely from one another and still possess the ability to model the surrounding world in three dimensions.
The next interesting ability of the mantis shrimp eye that the authors discussed was its ability to qualitatively detect polarized light. Most objects reflect light of a specific wavelength which gives rise to color vision. In a similar fashion, most objects also reflect light with a certain polarization that is characteristic of the material itself and mantis shrimp have the unique ability to detect and distinguish different planes of polarization, allowing them to identify materials at a distance.
On a final but similar note, the authors also suggest that the mantis shrimp eye also might possess the extremely unique ability to make sense of circularly polarized light. Circularly polarized light is an emergent property of the reflected light of some metals and membranes, and the authors seem to believe that the shrimp’s R8 receptor may act as a quarter-wavelength retarder which would allow the animal to convert circularly polarized light into linearly polarized light which they could then sense using their previously described polarized light receptor system.
The most important conclusion the authors suggest can be drawn from this paper is the parallel processing systems used to detect all of these different properties of light. Since most of the shrimp’s ommatidia or photoreceptors are specific for detecting a single light property, little higher level processing of the information is needed. This layout, they say, is a potent model for the creation of machine vision systems as little higher level processing is needed for extremely precise color vision. The authors think that this sort of thinking – drawing ideas for mechanical systems through the design of biological ones - will be increasingly important in the future. That aside, the mantis shrimp is an incredible animal and the inner workings of the eye are still very much a mystery and will require much more research to fully understand.

Parallel Processing and Image Analysis in the Eyes of Mantis Shrimps – The Biological Bulletin

The Art of Thriving -New Scientist

Ayahuasca is found to produce life-changing visions but can it also produce life-changing cures?

“As I closed my eyes, images – if they can be called such – began racing at an ever-increasing speed before me. Swirls of colors, shapes, forms, textures and sounds simply overpowered me to the point where I became immobile. Like many others before me, no doubt, I became somewhat frightened. What had I let myself in for? When I opened my eyes, the phantasmagoria of forms vanished, and I saw myself in the same room with the others”

Donald M. Topping’s description is very similar to the accounts many others have given. He brought up many questions on the vividness of visions produced after his very first ingestion of the hallucinogenic brew Ayahausca.  What underlying brain mechanisms allow potentially healing, uplifting and fearful experiences to occur behind closed eyelids?  That is what Draulio B. de Araujo and others sought out to find.

Ayahausca is a thick, brown potion served orally as a tea decoction made of a bush (Psychotria viridis), which is a rich source of N,N-dimethyltryptamine (DMT), and a liana (Banisteriopsis caapi) containing beta-carbolines (such as harmine, harmaline, and tetrahydroharmine).  The mixture of these two plants allows for the inhibition, by the beta-carbolines, of monoamine oxidase (MAO) ultimately causing DMT to be psychoactive after ingested.  Naturally, when DMT is orally ingested by itself, it is inactivated by MAO.  Soon after ingestion, the levels of 5-HT rise to incredible amounts.  The unnatural changes in brain chemicals as a result of Ayahuasca are believed to cause the powerful visual hallucinations that have been continuously reported.

Using functional Magnetic Resonance Imaging (fMRI), Arauji et. al., the Brain Institute at the Federal University of Rio Grande do Norte took in ten participates whom were all frequent Ayahuasca users and photographed their brains before and after an ingestion of 120-200 mL of Ayahuasca to see where activation in the brain takes place.  A closed-eyes imagery task was completed for both stages.  The imagery task included three conditions: viewing natural images (people, animals, or trees), mentally generating the previously seen images, and then viewing a scrambled version of the image presented in the first condition.  The scrambled image served as a baseline.  Psychiatric scales were also applied at intervals of 0, 40, 80, and 200 min after ingestion to detect symptoms of psychosis and mania.

Results would demonstrate an overall increase in the psychiatric scales after Ayahuasca intake, with a significant increase at 40 and 80 min.  The mean time for DMT in the Ayahuasca mixture to reach its peak concentration, T_max, is 90-120 minutes.  This would also explain why an Ayahuasca experience can last for several hours.  Results from the fMRI data showed significant activity in the occipital, temporal, and frontal cortical areas which are involved with vision, memory, and intention, respectively.

BOLD responses before and after Ayahuasca intake

Moreover, the activity in the occipital areas (BA17, BA19, and BA7) was significant because the BOLD signal amplitude after intake increased during the imagery condition, but not during the natural image condition. It is also worth mentioning that the increased activity of the BA17 location in the occipital region, which works with the cuneus and lingual gyrus, corresponds to the peripheral visual field.  This area may play a major role in why post-Ayahausca imagery is so intense even behind closed eyelids.  Ayahuasca also induced activity in temporal areas in the parahippocampal cortex (BA30) and the retrosplenial cortex (BA37) during the imagery condition, which are areas that deal with the retrieval of episodic memories and the processing of contextual associations.  In addition, frontopolar cortex (BA10) activity was also increased during the imagery condition perhaps because subjects intentionally create the images in their minds and interestingly enough, was the only area to produce a positive BOLD signal during the imagery condition before the intake and then potentiated after intake.

In the Amazon jungle, Kira Salak, a writer for National Geographic, photographs Shamans during an ayahuasca ceremony in Peru.

While my interest continues to grow about this psychotropic plant tea, I can rest assured that I know how my primary visual cortex activity can be intensified and like others be able to experience another dimension of reality behind closed eyes.  Besides its original use in select South American religious ceremonies, Ayahuasca can be used for therapy. People like Donald M. Topping, after going through several sessions of Ayahuasca ingestion, left his oncologist’s office one day with his cancer activity indicator below normal.  Many more have left with their symptoms of depression and anxiety miraculously gone, which can also be seen in another study by R.G. Santos et. al. where they suggest Ayahuasca can produce beneficial effects on mood and anxiety.  Even after its many centuries of use there is still much to be learned about the neural basis of Ayahuasca’s potent psychological effects. Unraveling the mystery of Ayahuasca could potentially be utilized in the future as a readily available alternative medicine.

Seeing with the eyes shut: Neural basis of enhanced imagery following ayahuasca ingestion
– Human Brain Mapping

Effects of ayahuasca on psychometric measures of anxiety, panic-like and hopelessness in Santo Daime members – Journal of Ethnopharmacology

Human Pharmacology of Ayahuasca: Subjective and
Cardiovascular Effects, Monoamine Metabolite Excretion, and
Pharmacokinetics – JPET

Human Pharmacology of Ayahuasca: Subjective and Cardiovascular Effects, Monoamine Metabolite Excretion, and Pharmacokinetics – National Geographic

Ayahuasca and Cancer: One Man’s Experience – Maps.org

Most would agree that the most important of our basic senses is sight. Without it, many basic forms of communication fall apart, the vibrance of the world around us dulls, and our understanding and ability to sense the complexity of the physical world diminishes. Without the ability to see, it would logically be impossible to portray our surroundings artistically in a coherent and visually realistic manner…

…wait…what?

Esref was born without the privilege of sight. As a result, he never developed the thalamo-cortical projections from the lateral geniculate nucleus (LGN) to the primary visual cortex necessary for sight perception. However, instead of letting his occipital lobe go to waste, Esref’s brain adapted by using that same cortical real estate for other senses, primarily touch.

With Esref’s enhanced sense of touch he claims he can, “see more with his fingers than sighted people can see with their eyes.” A bold statement: after all, Esref has no idea what seeing is like. Conversely, sighted people don’t know what the sense of touch is like when the visual cortex becomes involved, so can we really deny his claim? The circular nature of this subjective discussion renders both opinions null but it does raise the question: is a subjective experience a product of the sensory modality involved or is it a product of the cortical area involved? And what exactly is Esref subjectively perceiving when he is feeling his way through a landscape? Is it as vivid as the subjective experience that sighted people perceive? It seems this question is impossible to resolve but seeing the landscapes Esref paints makes one believe that he is indeed sensing the world just as vividly as the rest of us.

Esref provides a new perspective on perception which throws a kink into anyone’s previously held beliefs about subjective experience and raises many internal questions. Personally, this new perspective leaves me with one question in particular: we can all agree that the 2003 blockbuster Daredevil was horrible, but wasn’t the rooftop rain scene where the blind Ben Affleck uses the sound of the raindrops on Jennifer Garner’s face to create a mental construct of her one of the most forward thinking, cognitive science-inspired scenes in all of cinematography?

Foreshortening, convergence and drawings from a blind adult – Perception

For patients who have lost their sight to various eye diseases, artificial retina technology allows them to experience limited vision once more.

The external parts of the artificial retina device include glasses with a mounted camera and a small computer.

The device also includes an electrode implanted onto the patient’s retina. When the camera “sees” an image, the computer is able to translate these into a pattern of neural signals. This pattern is then transmitted to the implanted electrode, and directly stimulates the optic nerve. These signals are then able to be processed by the brain and interpreted as very rudimentary images.

The first artificial retina to be implanted in a patient, known as Argus I, included only sixteen electrodes that stimulated the optic nerve. However, the patient with this implant was still able to tell the differences between light and dark, and could make out basic shapes. The newer version of the technology, Argus II, now includes sixty electrodes. However, it is still limited in that patients can only tell the differences between light and dark areas, and can only see shapes, outlines, and blurs, and not detailed images. Regardless, this is a large improvement over no sight, and patients with the implant are satisfied with simply a partial regain of their vision, and are hopeful that the technology will continue to improve. As of late, a third model of the artificial retina is in development, and will include over 200 electrodes.

Though the project began almost ten years ago, the implant has recently been approved for patients in Europe. The company has not yet submitted approval to the FDA, but hopes to do so by the end of this year.

Second Sight – How is Argus II Designed to Produce Sight?

CBS News HealthPop – First Artificial Retina Approved in Europe

US Department of Energy Office of Science – About the Artificial Retina Project

Finding Nemo's Marlin

In Disney/Pixar’s “Finding Nemo,” Marlin and Dory are swimming through murky waters en route to Sydney Harbor. Marlin suddenly exclaims, “Wait, I have definitely seen this floating speck before. That means we’ve passed it before and that means we’re going in circles and that means we’re not going straight!” – and he is probably right.

Is it really possible that when we cannot see where we are going, we actually travel in circles? Souman et al. tested this belief through a variety of experiments. They found in all cases that when deprived of a visual stimulus, it is actually impossible to travel in a straight line.

The first set of experiments had participants travel through a wood without visual impediments (such as blindfolds). One set of subjects traveled through the woods when it was cloudy, the second set when it was sunny. All of the cloudy group walked in circles and walked in areas that they had previously been, without noticing they had crossed a previous path. In contrast, all of the subjects who could see the sun were able to maintain a course that was relatively straight and had no circles.

The experiment was also performed on blindfolded subjects in an open field.

Paths of Blindfolded Subjects

The blue paths correspond to the subjects that walked on cloudy days. Their paths are mostly curved with many circles. The small straight areas of walking are most likely caused by the setup of the trial – participants walked for a period of time, then were unblindfolded and allowed to walk to the starting point of the next walking block. Even so, when blindfolded, lack of a visual stimulus when blindfolded always resulted in walking in curved motions or in circles. This contrasts the yellow path; this subject walked on a sunny day, and maintained a straight course for a long distance.

What causes this strange phenomenon? Could it perhaps be subtle differences in leg length that introduce a bias to walk in one direction, thus accounting for the circular motion? Nope – the circle directions were still random. Adding shoe soles to add a more than subtle difference in leg length didn’t make a difference: the participants continued to walk in random circles.

Perhaps the only explanation is that our vision is so necessary for our daily lives that our body randomizes without it. This idea is demonstrated in studies in which subjects are kept in a room with constant lighting: their biological clocks become completely randomized with no night and day inputs. More studies should be performed to truly understand the importance of the visual system. Since we rely so heavily on vision, is it natural for movements to become randomized without it? Do those who are blind from birth experience the same walking in circles phenomenon? For now, the conclusion here is that the sensory systems are complex and there is still much work to be done in understanding this strange phenomenon. So, if you ever find yourself lost in murky Australian waters, you probably should not just keep swimming, but rather, ask a friendly passing whale for directions.

A Mystery: Why Can’t We Walk Straight? : Krulwich Wonders… – NPR

Walking Straight into Circles – Current Biology

Most of us are probably not strangers to the recent hub-bub in the media regarding the effects of video gaming on the brain.  From whinny mothers and senators complaining that graphic video games predispose our youth to violence and damage their minds, to the claims that daily “brain training” video game exercises can improve your overall mental well-being, it can be hard to determine just how video games are actually affecting our brains.  While the jury is still out as to whether or not violent video games overload the amygdala or if playing Brain Age everyday on your Nintendo DS can boost your memory and cognitive abilities, several studies produced in the last year or so have made some very interesting discoveries regarding the effects of gaming on the brain.  Though many of us may want to hear that playing StarCraft all day will predispose us to being strategic wizards and give us an edge at the next chess match, such is not the case.  The actually findings, however,  may still surprise you.

When you think of mentally stimulating activity in the realm of video games, you probably wouldn’t think of something like Call of Duty or the Prince of Persia as a game that would really get synaptic efficacy churning.  One would probably be more inclined to attribute that to electronic chess, or puzzle games like Tetris or Bejeweled, or even a tactical strategy game like Command and Conquer.  According to most independent studies into video gaming, however, it actually has been shown that fast paced, action gaming (and more commonly first person shooter games) just like Call of Duty are the only types of video games that provide any beneficial effects on the brain.  That’s right, your annoying roommate and all his obnoxious friends playing Halo at 3 am while you are trying to devise the perfect battle plan in WarCraft are doing something more mentally constructive than you!  How exactly though do video games provide any benefit (karma, magic, summoned magical demons!?) and what areas of the brain do they act upon?

By testing the reaction times of groups of patients both with and without extensive video gaming experience, researchers C. Shawn Green and Daphne Bavelier seem to have provided evidence that playing video games can substantially boost one’s overall attentional skills.  Unlike subjects without any experience playing video games, Green and Bavelier observed that gamers exhibited a much stronger ability to fixate upon specific visual and spatial cues while filtering out superfluous ones.  Subjects with gaming experience also displayed much faster reaction times in the spatial localization and object recognition tests that Green and Bavelier administered to them.  Even more interesting was that the researchers observed that these attentional abilities were not just specific to the test paradigms themselves, and could be applied to multiple other tests and situations with similarly above average results.

When you consider the circumstances of the kind of video games that these subjects are used to performing under, these results seem to make sense.  The action and pace of the games are fast and sporadic, with stimuli randomly popping up all over the place.  The gamers are constantly conditioned and trained to respond quickly to certain stimuli, while filtering other unimportant stimuli out (and of course, they are rewarded for proper responses by either advancing further in the game or winning in general).  Another important aspect of these games that Bavelier points to is the fact that there is no set of right/wrong answers or a specific learning paradigm in them due to how random the games are.  For this reason, and due to the fast pace such gameplay demands, Bavelier and Green also speculate that action video gaming benefits the decision making skills of gamers as well by, again, forcing them to think and react accurately and quickly to specific stimuli while ignoring/rejecting others that would lead to a mistake in the game (a skill that the two have coined as probabilistic interference).  This goes strongly against all that admonishment your mother would give you back in the day about rotting your brain away in front of the Super Nintendo.  In actuality, you could have been sharpening it!

General model of visuomotor processing and the relative brain regions involved in such tasks.

Enhanced spatial attention and quick decision making are apparently not the only unexpected benefit of video gaming; according to a research team in Toronto, Canada, extensive gaming can also improve hand-eye coordinative tasks and overall visuomotor abilities. Through performing fMRI analysis on several test subject both with extensive gaming experience (or week long game training) and no video game experience while they conducted different visuomotor tasks (navigating a maze with joysticks, pointing in one direction while facing the other, etc.), it was found that those with gaming experience performed leagues better than those without.  Even more curious, however, was that it the gamers seemed to perform so much better and quicker than the non-gamers because they utilized a completely different neural network than the non-gamers to process the test data!  While non-gamers primarily employed their parietal lobes in the visuomotor tasks, the gamers utilized the prefrontal, premotor, primary sensorimotor and a larger portion of their parietal regions to process and respond to the tasks.

This shift in processing channels, however, did not result from viewing test information differently, or processing it differently in the retina; instead it came through a complete reorganization of the visuomotor pathways in the brain, developing a more efficient and effective pathway!  Much like Bavelier and Green, the Canadian research team seems to attribute these changes to the fast pace of action gaming and the high attention to detail that said games demand of the players.  Not only must the players translate the movements they desire for their in-game character onto the screen itself (and memorize multiple button patterns to do so), but they must constantly react as quickly and accurately as possible if they want to be able to keep playing.  The researchers even joke at one point that with all the training such games offer to the players in speed, precision and accuracy with hand-eye coordinative movements, many of them could be potential candidates for surgeons someday!

Pwning noobs today, performing life-saving laparoscopic surgery tomorrow.

Despite the fact that video games may not give us amazing deductive powers by playing puzzle games or promote superhuman prefrontal abilities through strategy gaming, they can help us respond faster and develop different processing pathways for visuomotor tasks (a prospect that could prove to be very beneficial for Alzheimer’s patients who are highly impaired in parietal visuospatial performance).  While we know that joystick and button-pad gaming can foster such benefits, it would be interesting to see if any of the new “motion controlled” types of video games could increase the development of such skills by forcing the player to move the controller in the actual direction of movement or action in the game (as pioneered by Nintendo’s Wii and the Playstation’s Move).  This would be most interesting to study in Microsoft’s Xbox Kinect console, a system that translates real time motion captured movements into the game itself, so a player can use his/her arms, legs and entire body as the controllers!  Could this foster enhanced visuomotor skills as well, or only serve to make you look silly as you prance around in front of the TV screen?

Sources and Related Reading:

Neuroscience News – Gamers Have Advantage in Performing Visuomotor Tasks

Medical News Today – Sharpening Decision-Making Skills Through Action Video Game Play

Nature Neuroscience – Carrot Sticks or Joysticks: Video Games Improve Vision

Cortex – Extensive Video Game Experience Alters Cortical Networks for Complex Visuospatial Transformations

PubMed Central – Effects of Action Video Games on the Spatial Distribution of Visuospatial Attention

Vision is one of the most impressive functions of the human brain. It interprets nothing but electromagnetic waves and paints a glorious picture of our daily existence from the scattered chaotic sea of intertwining light waves that we call home. Many see their vision deteriorate and the world blur as time goes on and these problems can be corrected by optometry, but blindness comes on like a relentless infidel for more than two million people worldwide in the form of retinitis pigmentosa (RP). RP is a heritible genetic disorder that leads to degeneration and loss of function in the retina’s photoreceptor cells, and can lead to full blindness in a matter of years. There is no cure or treatment for RP, but new research may change that very soon.

TOP: Macroscopic human eye (left) and rod and cone cell arrangement on the retina (right). BOTTOM: Normal human retina (left) and human retina with retinitis pigmentosa (right)/(Source: Medical-Look.com)

Vision starts in the photoreceptor when light activates rhodopsin, a G-protein coupled receptor pigment consisting of light sensitive opsin and retinal. Light triggers a conformational change in retinal that kick starts a G-coupled visual cascade and the flow of visual information to the brain. In retinitis pigmentosa, rhodopsins in the photoreceptors become insensitive to light starting in the rod cells, and blindness sets in gradually. Rod cells are used in low light and deteriorate first, leading to night blindness, and dysfunction in cone cells used for color vision and acuity sets in until full blindness plagues the individual. Fortunately, a team of French scientists has investigated this degradation and has found a way to combat it by reactivating the photoreceptor cells through genetics. Their study was featured in the July 23rd issue of Science.

Artificially colored micrograph image of retinal rods (yellow-green) and cones (blue). (Credit: Science Photo Library @ sciencephoto.com)

The scientists isolated an achaebacterial rhodopsin analog called halorhodopsin that functions in the yellow and green wavelength range. They then introduced a halorhodopsin encoding gene into retinitis pigmentosa model mice via a viral vector and also created a control group. In their experiments, it was found that both slow and fast degrading retinal cells in the experimental mice regained their light sensitivity in response to integration of halorhodopsin into their insensitive photoreceptor cells. Electrical responses were recorded from ganglion cells (the third tier cell in the visual cascade) and healthy photoreceptor spikes were observed in response to light stimulation. Most importantly, lateral inhibition (the mechanism by which the brain discriminates edges of objects) was fully preserved, while mono-directional movement was retained. Halorhodopsin mice also performed significantly better than the control RP mice in a battery of visually guided tasks, demonstrating that their photoreceptors had been successfully resensitized by halorhodopsin integration. The scientists also tested the resensitizing ability of halorhodopsin on cultured human retinal cells. They were successful in integrating halorhodopsin into human cells via viral vectors, but could not conduct any clinical trials. However, photoreceptors expressing halorhodopsin demonstrated photocurrents and photovoltages that would be adequate to restore human vision.

Theoretical device that allows a halorhodopsin treated patient to see by projecting patterned light onto the eyes derived from camera input. (Credit: Y. Greenman/Science)

This opens the door to treatment of retinitis pigmentosa in the genes – the same place where it starts. Although halorhodopsin therapy will not fully restore all wavelengths in human vision, it can still serve as a tool to bring restore vision in the blind through optical devices. For example, an RP patient could be treated with halorhodopsin gene thearpy, then outfitted with a device that images the visual field and translates it into halorhodopsin recognizable wavelengths. This light mosaic is then projected onto the patient’s eyes and the can “see” what is in front of them. The supplied image of the device is from a perspective article in the beginning of the current issue of Science.

View the full text Science article here (HTML) or here (PDF) and the perspective piece about the article here. Be sure to discuss in the comments!

Sources:

Seeing the Light of Day - Science (Perspective)

Genetic Reactivation of Cone Photoreceptors Restores Responses in Retinitis Pigmentosa - Science (Research Article)