Vision Loss and Other Sensory Deficits

Sensory deficits such as blindness and low vision are very common forms of disability, affecting over 300 million people worldwide according to World Health Organization estimates.

Loss of vision has many causes, and while some cases are treatable or preventable, many others are not. In particular, there is currently no way to reverse damage to the retina or the visual part of the brain, and new treatments are urgently needed for these conditions.

Researchers at the McGovern Institute are studying how the visual system works, how it develops and adapts to the visual world, and how it responds to deprivation or disease. Insights from this fundamental work will be central to the development of new therapeutic approaches for visual and other deficits. McGovern researchers are also collaborating with colleagues in the MIT School of Engineering to develop new technologies such as implantable prosthetic devices that could eventually be used to treat blindness and other disorders.

Faculty members whose research is relevant to vision loss and other sensory deficits include:

Ed Boyden

Ed Boyden is a pioneer in the development of optogenetics, a technology that involves genetically manipulating neurons so that they can be controlled by light. Optogenetics is widely used as a research tool, and also has many potential therapeutic applications, including the treatment of sensory deficits. For example, it may be possible to restore light sensitivity to a retina that is damaged through diseases such as retinitis pigmentosa. Boyden and collaborators at the McGovern Institute recently reported the first use of optogenetics in primates, an essential step on the road to eventual human therapeutic applications. Boyden is also a co-founder of Eos Neuroscience Inc., an early-stage biotech company that intends to develop optogenetic technology as a treatment for retinal blindness.

Martha Constantine-Paton

Martha Constantine-Paton studies how the mammalian brain becomes wired in response to experience. This is a fundamental question for normal development and is also relevant to many developmental problems, including sensory deficits. For example, amblyopia, one of the most common causes of visual problems in children, results from a failure in the normal development of the brain’s visual pathways. Normal vision requires the brain to combine signals from both eyes, but if the movement or function of one eye is impaired (for example, through strabismus or astigmatism), then the brain is unable to learn how to combine the signals. If treated during early childhood, while the brain is still malleable in response to visual experience, these problems are usually self-correcting. Beyond this so-called ‘critical period,’ however, the brain loses its plasticity and is unable to compensate. As a result, depth perception and visual acuity may be permanently impaired. Constantine-Paton studies the synaptic mechanisms that underlie this developmental plasticity. Her work focuses specifically on the visual system, but the principles that emerge are also relevant to other senses and to higher cognitive functions such as language acquisition.

Bob Horvitz

Bob Horvitz uses the nematode worm Caenorhabditis elegans as a model system to understand the development and function of the nervous system. Among the many areas that have been illuminated by his work is the genetic control of cell survival and cell death. For example, one recent study identified a gene that promotes the survival of certain sensory neurons in worms, through a novel genetic pathway that is different from any previously known cell survival mechanism. Like many aspects of worm biology, this mechanism appears to be shared with mammals. Mutations in the mouse counterpart of the worm gene lead to hearing loss, a result of progressive degeneration of the sensory cells of the inner ear. Understanding the mechanisms that control sensory neuronal death may lead to new strategies for preventing sensory deficits such as retinal blindness and hearing loss that result from death of human sensory neurons.

Nancy Kanwisher

Nancy Kanwisher studies human visual perception using a combination of neuroimaging and behavioral testing. One of her interests is how the visual system develops in response to experience, both in normal development and in visual deficits such as blindness. For example, macular degeneration (MD), one of the most common causes of blindness, causes blind spots in the visual field of one eye, and Kanwisher’s studies on MD patients have revealed the plasticity of the brain’s response to visual deprivation. Her recent work demonstrates that the brain can respond very rapidly to visual deprivation, suggesting that the brain has a network of silent connections that underlie its plasticity.

Rebecca Saxe

Rebecca Saxe studies the neural basis of human social cognition and abstract thought. The Saxe Lab uses imaging technologies and behavioral studies to understand how individuals view the mental states of other people (called 'theory of mind'), make moral judgments about others, and construct complex and abstract thoughts about how other individuals think about the world around us. Saxe is interested in how theory of mind develops in children with developmental difficulties, including those with sensory deficits. Her lab is currently investigating theory of mind development in blind children, who learn of others’ beliefs through hearing instead of sight, and deaf children, who may be exposed to language later in life than hearing children.

Sensory prosthetics

Although prevention is the ultimate goal, for patients with irreversible vision loss, sensory prosthesis is an appealing therapeutic strategy. This is already well established in the case of hearing loss. Cochlear implants, which convert sounds into direct electrical stimulation of sensory nerves, have been used to treat almost 200,000 patients worldwide.

A prosthetic device to treat blindness would be a major advance, but two major challenges must be overcome to make this a reality. First, if we are to deliver sensory information directly to the brain, we need to understand how the brain normally represents information, and what types of signals should be inserted in order to create an artificial stimulus that the brain can interpret. It will also be important to understand the plasticity of the brain, since the brain needs to learn to interpret the information. Second, we must overcome the engineering challenge of building effective prosthetic devices.

Many groups at the McGovern Institute are studying the first problem. James DiCarlo, Robert Desimone, Nancy Kanwisher, and Tomaso Poggio are all engaged in studies of sensory coding, using a variety of technologies and systems.

Several groups are also working on the technology needed to build brain-machine interfaces, with support from McGovern Institute Neurotechnology MINT Program. For example, Michale Fee collaborates with MIT electronic engineers to develop and test a wireless low-power stimulator and associated electronics that will be needed to build an effective neural prosthetic device. Ed Boyden is collaborating with experts in microfabrication to develop implantable optical devices that can both drive and record neural activity, and that could eventually form the basis of a new generation of interfaces between neural and electronic circuits.

Selected References

Millisecond-timescale optical control of neural dynamics in the nonhuman primate brain.Han X, Qian X, Bernstein JG, Zhou HH, Franzesi GT, Stern P, Bronson RT, Graybiel AM, Desimone R, Boyden ES. Neuron. 2009 Apr 30;62(2):191-8.

Circuit-specific expression of channelrhodopsin restores visual function in blind rd1, rd16, and rho -/- mice. A. HORSAGER, J.-W. LIU, E. S. BOYDEN, A. C. ARMAN, B. C. MATTEO, A. P. SAMPATH, W. W. HAUSWIRTH (2009) Soc Neurosci. Abstr 403.6

The C. elegans protein CEH-30 protects male-specific neurons from apoptosis independently of the Bcl-2 homolog CED-9. Schwartz HT, Horvitz HR. Genes Dev. 2007 Dec 1;21(23):3181-94.

NR2A-/- mice lack long-term potentiation but retain NMDA receptor and L-type Ca2+ channel-dependent long-term depression in the juvenile superior colliculus. Zhao JP, Constantine-Paton M. J Neurosci. 2007 Dec 12;27(50):13649-54.

"Referred visual sensations": rapid perceptual elongation after visual cortical deprivation. Dilks DD, Baker CI, Liu Y, Kanwisher N. J Neurosci. 2009 Jul 15;29(28):8960-4.

Reorganization of visual processing in macular degeneration is not specific to the "preferred retinal locus". Dilks DD, Baker CI, Peli E, Kanwisher N. J Neurosci. 2009 Mar 4;29(9):2768-73.

Reorganization of visual processing in macular degeneration: replication and clues about the role of foveal loss. Baker CI, Dilks DD, Peli E, Kanwisher N. Vision Res. 2008 Aug;48(18):1910-9.

Reorganization of visual processing in macular degeneration. Baker CI, Peli E, Knouf N, Kanwisher NG. J Neurosci. 2005 Jan 19;25(3):614-8.

Wireless neural stimulation in freely behaving small animals. Arfin SK, Long MA, Fee MS, Sarpeshkar R. J Neurophysiol. 2009 Jul;102(1):598-60