Vilayanur S. "Rama" Ramachandran is a neurologist best known for his work in the fields of behavioral neurology and psychophysics. He is currently the Director of the Center for Brain and Cognition, Professor in the Psychology Department and Neurosciences Program at the University of California, San Diego, and Adjunct Professor of Biology at the Salk Institute for Biological Studies.
Ramachandran initially obtained an M.D. at Stanley Medical College in Madras, India, and subsequently obtained a Ph.D. from Trinity College at the University of Cambridge. Ramachandran’s early work was on visual perception but he is best known for his experiments in behavioral neurology which, despite their apparent simplicity, have had a profound impact on the way we think about the brain.
Ramachandran has been elected to fellowships at All Souls College, Oxford, and the Royal Institution, London (which also awarded him the Henry Dale Medal). He gave the 2003 BBC Reith Lectures and was conferred the title of Padma Bhushan by the President of India in 2007. He has been called “The Marco Polo of neuroscience” by Richard Dawkins and "the modern Paul Broca" by Eric Kandel. Newsweek magazine named him a member of "The Century Club", one of the "hundred most prominent people to watch" in the 21st century.
Ramachandran has published over 180 papers in scientific journals. Twenty of these have appeared in the highly prestigious scientific journal Nature, and many others have appeared in such journals as Science, Nature Neuroscience, Perception and Vision Research. He is author of the acclaimed book Phantoms in the Brain that has been translated into nine languages and formed the basis for a two part series on BBC Channel 4 TV (UK) and a 1-hour PBS special in the USA. He is the editor of the Encyclopedia of the Human Brain (2002), and is co-author of the bi-monthly "Illusions" column in Scientific American Mind. The two phases of his career can be summarized as follows:
He is credited with discovering several new visual effects and illusions; most notably perceived slowing of motion at equiluminance (when red and green are seen as equally bright), stereoscopic "capture" using illusory contours, stereoscopic learning, shape-from-shading, and motion capture. He invented (together with Richard Gregory) filling in of "artificial scotomas" and discovered a new "dynamic noise after effect". He also invented a class of stimuli (phantom contours) that selectively activate the magnocellular pathway in human vision and are now being used to diagnose dyslexia.
Ramachandran’s work (together with that of many other colleagues, including Patrick Cavanagh, Ken Nakayama, and Alan Gilchrist) initiated a "neo-gestalt" revolution in the study of vision – following the tradition of Irvin Rock, Bela Julesz, Julian Hochberg, and Richard Gregory (and the generation of Gestaltists prior to that: Kurt Koffka, Wolfgang Kohler, Stuart Anstis, and Max Wertheimer). This work helped inspire a new era of physiological experiments and AI modeling of visual processes.
Many of his visual illusions, including brief explanations of how they work are available on his website at Ramachandran illusions
When an arm or leg is amputated patients continue to vividly feel the presence of the missing limb a "phantom limb". In the early 1990’s Ramachandran began using this phenomenon as a probe for exploring neural plasticity in the adult human brain. Ramachandran suggested that phantom limbs might be due to changes in the brain, rather than in the peripheral nerves. The input from the limb is mapped on to the somatosensory cortex in an orderly manner, forming a representation which is referred to as the somatosensory homonculus. Input from the hand is located next to the input from the arm, input from the foot is located next to input from the hand, and so on. One oddity is input from the face is located next to input from the hand. Due to the way that the surface of the body is represented in the brain, stimulation to the cheek should elicit phantom limb sensations if the brain had reorganized after amputation, but not if the changes were simply peripheral. For example if, after arm amputation, the face on the same side of the body is touched the patient feels sensations in his/her phantom arm; the sensations (touch, temperature, vibration, etc.) are referred from the face to phantom in an organized manner (the somatotopic arrangement). Ramachandran and colleagues first demonstrated this remapping by showing that stroking different parts of the face led to perceptions of being touched on different parts of the missing limb.
Ramachandran conjectured (and showed using MEG) that when the arm is amputated the vacated cortical territory corresponding to the missing arm is “invaded” by neurons which respond to stimulation of the face which normally would only go to the face region of the cortical homonculus. Signals from the face would then activate the original hand area of cortex and higher brain centers interpret this activation as arising from the phantom hand. The results show that brain maps are highly malleable; not fixed at birth as was previously believed.
Most patients with phantom arms feel that they can move their phantoms but in many the phantom is fixed or "paralyzed", often in a cramped position that is excruciatingly painful. Ramachandran suggested that this paralysis was because every time the patient attempted to move the paralyzed limb, he or she received sensory feedback (through vision and proprioception) that the limb did not move. This feedback stamped itself into the brain circuitry through a process of Hebbian learning, so that, even when the limb was no longer present, the brain had learned that the limb (and subsequent phantom) was paralyzed. In order to overcome this learned paralysis, Ramachandran created the mirror box in which a mirror is placed vertically in front of the patient and had patients look at the mirror reflection of the normal arm so that the reflection was optically superimposed on the felt location of the phantom (thus creating the visual illusion that the phantom had been resurrected). Remarkably if the patient now moved his normal hand while looking at the reflection, he not only saw the phantom move (as expected) but felt it to move as well. In some patients this seemed to abolish the pain in the phantom. In others the phantom disappeared entirely – along with the pain – for the first time in years. The clinical usefulness of this mirror visual feedback (MVF) procedure has now been confirmed by several groups using double-blind placebo controlled trials. In the same series of studies, Ramachandran also found that merely creating the visual illusion of seeing the phantom being touched (using mirrors) sometimes evoked touch sensations in the phantom. Ramachandran also used phantom limbs to explore the perceptual correlates of the mirror neuron system in humans. Sensory neurons in the brain are activated in response to that person being touched, and a certain proportion of these same neurons also fire when someone watches another person, being touched (mirror neurons) as if the neuron was “reading” the other persons mind or “empathizing”. But the person watching someone else being touched does not normally experience the touch delivered to the other person presumably because the skin on his own hand is sending a null signal (to the non-mirror neuron type sensory neurons) that vetoes the output of mirror neurons. Consistent with this theory, Ramachandran found that when a patient with a phantom arm watched another person’s intact hand being rubbed, he actually felt his phantom being rubbed. Massaging the other persons hand appeared to relieve the pain in the phantom, an observation that might have clinical implications if confirmed.
Taken collectively, these results (together with the work of Michael Merzenich, Jon Kaas, Paul Bach-y-Rita, Alvaro Pascal-Leone, and others) have ushered in a new approach to brain function and neurological rehabilitation. The old picture of the brain as a set of autonomous modules hardwired at birth has been replaced with the view that the so-called brain modules are in a state of dynamic equilibrium with each other and with the sensory input. Many neurological disorders - but not all - may result from a shift in this equilibrium rather than permanent destruction of neural tissue. This is not only of considerable theoretical interest but also clinically useful because it implies that relatively simple procedures may be enormously effective in rehabilitation of brain function.
More recently, Ramachandran studied the neural mechanisms of grapheme-color synesthesia, a condition in which viewing black and white letters or numbers on a page evokes the experience of seeing colors. Ramachandran (with then PhD student, Edward Hubbard) showed that some synesthetes (those who experience synesthesia) were better able to detect "embedded figures" composed of one letter or number (for example a triangle composed of 2s) on a background of another number (for example 5s). This is a difficult task for people who do not experience synesthesia. However, some synesthetes report that the colors they see help them to find and identify the embedded shape. Their performance on behavioral tasks show that some synesthetes are better at this task than non-synesthetes.
Based on his previous work on phantom limbs, Ramachandran suggested that synesthesia may arise from a similar cross-activation between brain regions. However, rather than being within a single sensory stream, this form of cross-activation would occur between sensory streams, and is thought to be due to genetic differences, rather than neural re-organization. In fMRI experiments, increased activity in a color selective region (hV4) was found in synesthetes compared to non-synesthetes when they viewed letters and numbers that evoked synesthetic colors, compared with symbols that did not.