Project Prakash: Challenging the Critical Period

Abstract

Project Prakash is an organization that reverses congenital blindness in children and adolescents in rural India with the hypothesis that these children will be able to recover some of their vision even though their visual system did not develop normally. This hypothesis challenges the scientific dogma established by the Nobel-prize winning research of Hubel and Wiesel that the brain cannot adapt to visual input after being completely deprived of vision during the critical first few months and years of life. Dr. Pawan Sinha presented his work at the largest and most respected ophthalmological research meeting, the Association for Research in Vision and Ophthalmology (ARVO), in Fort Lauderdale, Florida, on May 4, 2011.

It is rare for a philanthropic mission to act in harmony with groundbreaking research as well as provide a scientific answer to a philosophical debate. Pawan Sinha, Professor of Vision and Computational Neuroscience at MIT, has managed to take on these challenges with amazing success in his mission, Project Prakash, which means “light” in Sanskrit. Project Prakash brings sight to blind children and adolescents in India while answering the age-old question of what the blind would see if their sight were restored. Sinha presented his work at the Association for Research in Vision and Ophthalmology (ARVO) meeting in Fort Lauderdale, Florida, on May 4, 2011.

The philanthropic arm of Project Prakash, based at the Schroff Charity Eye Hospital in New Delhi, has traveled to hundreds of villages and screened more than 7,000 children in rural India. Much of the blindness in India is due to reversible causes, such as childhood cataracts, congenital infections, and misalignment of the eyes. Often, these conditions are not corrected since there is little access to health care in villages that are thousands of miles from major metropolitan centers. As a result of the screenings, thousands are given glasses, eye patches, or other simple treatments to correct common eye problems. All aspects of care including examination, treatment, transportation, and hospital stay are provided free of charge to the children.

The scientific research performed at Project Prakash challenges one of the most basic tenets of visual research: that the visual system cannot regain function if children do not see during their first years of life. This is based on the logic that since the eye problems are not corrected when the children are young, their brain does not form the complex system of interconnections that would normally harness and process the rich information captured by their eyes.

In a series of classic experiments, Hubel and Wiesel showed that there is a so-called “critical period” for the brain to be stimulated to form these connections. If visual input is completely blocked, these connections are not able to form correctly, even when full visual input is provided months or years later [1]. This theory was based on a group of experiments in which cats were subjected to periods of visual deprivation by suturing their eyelids closed at different stages of visual development. The scientists found that kittens were not able to develop useful vision even if the period of visual deprivation only occurred during the first 3 months of life. When the experiment is performed on older cats, vision is completely unaffected by a period of visual deprivation. In keeping with this research, correctable eye problems are usually diagnosed soon after birth or in infancy and treated as soon as is safely possible in the United States. If a child’s eye problem is not caught at birth or within the first few months of life, the child’s vision is considered compromised.

The five children and adolescents in the recent study published by Dr. Sinha’s laboratory in Nature Neuroscience [2] represent a truly unique study population: They have causes of blindness that can be completely reversed even though they are quite advanced in age. Four of the children (Subjects YS: 8-year-old male; BG: 17-year-old male; SK: 12-year-old male; and PS: 14-year-old male) were born with cataracts, and the fifth (Subject PK: 16-year-old female) has corneal opacities. These conditions cloud the normally clear tissues of the front of the eye, blocking the child’s view of the world. The lens and cornea both can be safely removed and replaced with synthetic or donated tissues. Thus, these children allowed for study of how the visual system functions when being activated for the first time in adolescence.

In this study, five subjects had their blindness surgically corrected and were immediately presented with three-dimensional Lego-like objects and tested to determine if they could recognize objects by sight that they previously were acquainted with only by touch. The study had three conditions: tactile presentation/tactile test, visual presentation/visual test, and tactile presentation/visual test. The subject was given an object during a study period and then presented with the studied object and a distractor object. The subject’s task was to choose the studied object. The first two conditions confirmed that all subjects were able to reliably identify an object both by sight and touch before it tested a subject’s ability to recognize an object by sight after having studied it with touch alone. The study also re-tested subjects several days to several months after their initial surgery to follow up changes in their visual abilities.

The research also directly answers one of the great philosophical questions, Molyneux’s problem [3], which asks whether a blind person who has his sight restored will be able to recognize an object previously known only by touch. If this premise were true, John Locke and other philosophical empiricists would believe that this confirmed the existence of an innate conception of an object that was separate from all sensory input. In modern neuroscience research, this could mean that neurons dedicated to cross-sensory interaction were present even though visual information had not been provided. So what was the answer? The study found that immediately after surgery, subjects were able to identify objects with 58 percent accuracy, only slightly better than random chance. So, in other words, a resounding “No.” However, within a week, their performance increased considerably to above 80 percent accuracy. This shows that although the sight-deprived visual system does not operate optimally, it seems to have a great degree of plasticity even when deprived of visual input during the critical period.

Project Prakash and these few brave children have offered each other an exceptional opportunity they would not otherwise have. These children have contributed greatly to the field of vision research and neuroplasticity by sharing their personal experiences with the world. Project Prakash will continue to recruit new children and teenagers with reversible causes of blindness and study these children closely to learn exactly how their vision develops after surgery and how it differs from children who have lived with vision for their entire lives.

Initial follow-up work in the laboratory has focused on facial recognition and which aspects of a face are critical to recognition such as color, degree of blur, and rotational orientation [4]. By testing different attributes of an image, the research team hopes to gain insight into how the vision naive brain processes visual information and what strategies it uses to organize the rudimentary visual function it recovers.

Glossary

ARVO

Association for Research in Vision and Ophthalmology