Search PubMed⌕ Search

Biomedical subjects

V S Ramachandran

Publications and source records attributed to V S Ramachandran.

At least 19 recordsLinked to original sources
PubMed2006

Situational therapy for Wernicke's aphasia.

Patients with Wernicke's or expressive aphasia are able to produce fluent speech, however, this speech may be complete gibberish sounds and totally incomprehensible, or even when comprehensible to a degree is often laced with severe errors and abnormalities such as verbal and phonemic paraphasias and neologisms. Furthermore, patient's with Wernicke's aphasia have poor to no understanding of speech or language. There is no proven method for rehabilitation of Wernicke's aphasia, or even much guidance for physicians or speech therapists to treat Wernicke's aphasia patients. In contrast to their poor to non-existent communication skills using speech or other forms of language, it has long been appreciated informally and formally that Wernicke's aphasia patients are able to communicate well, even normally, using non-verbal means such as actions, movements, props, gestures, facials expressions, and affect. Furthermore, in non-language domains Wernicke's aphasia patients can show normal memory and learning abilities. Thus, we here suggest that the non-language communication channels of Wernicke's aphasia patients be channeled and utilized in their functional rehabilitation: Specifically, we suggest that therapy for Wernicke's aphasia patients should consist of placing patients in real or simulated important functional situations--e.g., buying food, taking transport--and let the patients train and learn to use and hone their non-language communication means and skills for improved practical functioning.

Aphasia, Wernicke↗
PubMed2005

Neurocognitive mechanisms of synesthesia.

Synesthesia is a condition in which stimulation of one sensory modality causes unusual experiences in a second, unstimulated modality. Although long treated as a curiosity, recent research with a combination of phenomenological, behavioral, and neuroimaging methods has begun to identify the cognitive and neural basis of synesthesia. Here, we review this literature with an emphasis on grapheme-color synesthesia, in which viewing letters and numbers induces the perception of colors. We discuss both the substantial progress that has been made in the past fifteen years and some open questions. In particular, we focus on debates in the field relating to the neural basis of synesthesia, including the relationship between synesthesia and attention and the role of meaning in synesthetic colors. We propose that some, but probably not all, of these differences can be accounted for by differences in the synesthetes studied and discuss some methodological implications of these individual differences.

Attention↗
PubMed2005

V.S. Ramachandran.

Explore the source record for details and available documents.

Career Choice↗
PubMed2003

Projecting sensations to external objects: evidence from skin conductance response.

Subjects perceived touch sensations as arising from a table (or a rubber hand) when both the table (or the rubber hand) and their own real hand were repeatedly tapped and stroked in synchrony with the real hand hidden from view. If the table or rubber hand was then 'injured', subjects displayed a strong skin conductance response (SCR) even though nothing was done to the real hand. Sensations could even be projected to anatomically impossible locations. The illusion was much less vivid, as indicated by subjective reports and SCR, if the real hand was simultaneously visible during stroking, or if the real hand was hidden but touched asynchronously. The fact that the illusion could be significantly diminished when the real hand was simultaneously visible suggests that the illusion and associated SCRs were due to perceptual assimilation of the table (or rubber hand) into one's body image rather than associative conditioning. These experiments demonstrate the malleability of body image and the brain's remarkable capacity for detecting statistical correlations in the sensory input.

Galvanic Skin Response↗
PubMed2003

Modular organization of adaptive colouration in flounder and cuttlefish revealed by independent component analysis.

Flounders and cuttlefish have an impressive ability to change colouration, for camouflage and, in the case of cuttlefish, for communication. We pursue the hypothesis that these diverse patterns are created by combining a small number of distinct pattern modules. Independent component analysis (ICA) is a powerful tool for identifying independent sources of variation in linear mixtures of signals. Two versions of ICA are used, one assuming that sources have independence over time, and the other over space. These reveal the modularity of the skin colouration system, and suggest how the pattern modules are combined in specific behavioural contexts. ICA may therefore be a useful tool for studying animal camouflage and communication.

Adaptation, Physiological↗
PubMed2001

Autonomic responses of autistic children to people and objects.

Several recent lines of inquiry have pointed to the amygdala as a potential lesion site in autism. Because one function of the amygdala may be to produce autonomic arousal at the sight of a significant face, we compared the responses of autistic children to their mothers' face and to a plain paper cup. Unlike normals, the autistic children as a whole did not show a larger response to the person than to the cup. We also monitored sympathetic activity in autistic children as they engaged in a wide range of everyday behaviours. The children tended to use self-stimulation activities in order to calm hyper-responsive activity of the sympathetic ('fight or flight') branch of the autonomic nervous system. A small percentage of our autistic subjects had hyporesponsive sympathetic activity, with essentially no electrodermal responses except to self-injurious behaviour. We sketch a hypothesis about autism according to which autistic children use overt behaviour in order to control a malfunctioning autonomic nervous system and suggest that they have learned to avoid using certain processing areas in the temporal lobes.

Adolescent↗
PubMed2001

Psychophysical investigations into the neural basis of synaesthesia.

We studied two otherwise normal, synaesthetic subjects who 'saw' a specific colour every time they saw a specific number or letter. We conducted four experiments in order to show that this was a genuine perceptual experience rather than merely a memory association. (i) The synaesthetically induced colours could lead to perceptual grouping, even though the inducing numerals or letters did not. (ii) Synaesthetically induced colours were not experienced if the graphemes were presented peripherally. (iii) Roman numerals were ineffective: the actual number grapheme was required. (iv) If two graphemes were alternated the induced colours were also seen in alternation. However, colours were no longer experienced if the graphemes were alternated at more than 4 Hz. We propose that grapheme colour synaesthesia arises from 'cross-wiring' between the 'colour centre' (area V4 or V8) and the 'number area', both of which lie in the fusiform gyrus. We also suggest a similar explanation for the representation of metaphors in the brain: hence, the higher incidence of synaesthesia among artists and poets.

Auditory Perception↗
PubMed2000

Phantom limbs and neural plasticity.

The study of phantom limbs has received tremendous impetus from recent studies linking changes in cortical topography with perceptual experience. Systematic psychophysical testing and functional imaging studies on patients with phantom limbs provide 2 unique opportunities. First, they allow us to demonstrate neural plasticity in the adult human brain. Second, by tracking perceptual changes (such as referred sensations) and changes in cortical topography in individual patients, we can begin to explore how the activity of sensory maps gives rise to conscious experience. Finally, phantom limbs also allow us to explore intersensory effects and the manner in which the brain constructs and updates a "body image" throughout life.

Adult↗
PubMed1999

Can mirrors alleviate visual hemineglect?

Following right hemisphere stroke, many patients display an indifference to objects and events in the left side of the world ('neglect'). Here, we describe a new technique that might help accelerate recovery from neglect. The patient sits at a table and a mirror is propped vertically on the patient's right side in the parasagittal plane, so that when the patient rotates his head rightward and looks into the mirror, he sees the neglected side of the world reflected in the mirror. Our question was: since the sensory information was now coming from the non-neglected left side, would this somehow make him overcome the neglect? In pilot experiments, two types of responses were seen: (a) In one subset of patients the presence of the mirror seemed to enhance the patients' awareness of the neglected field, so that they reached correctly for an object that was shown in the neglected field. Will repeated practice with this task accelerate recovery from neglect? (b) The second group of patients kept reaching into the mirror to grasp the reflection or kept groping behind the mirror ('mirror agnosia'). If the mirror was placed in the coronal position and the object placed behind their head, then some of these patients (from group B) reached correctly for the object. Quite apart from its obvious theoretical implications, we believe this technique might provide a new approach for the treatment of visual hemineglect.

Brain↗
PubMed1998

Consciousness and body image: lessons from phantom limbs, Capgras syndrome and pain asymbolia.

Words such as 'consciousness' and 'self' actually encompass a number of distinct phenomena that are loosely lumped together. The study of neurological syndromes allows us to explore the neural mechanisms that might underlie different aspects of self, such as body image and emotional responses to sensory stimuli, and perhaps even laughter and humour. Mapping the 'functional logic' of the many different attributes of human nature on to specific neural circuits in the brain offers the best hope of understanding how the activity of neurons gives rise to conscious experience. We consider three neurological syndromes (phantom limbs, Capgras delusion and pain asymbolia) to illustrate this idea.

Body Image↗
PubMed1998

Acute plasticity in the human somatosensory cortex following amputation.

We studied a patient after amputation of an arm and found that in less than 24 h stimuli applied on the ipsilateral face were referred in a precise, topographically organized, modality-specific manner to distinct points on the phantom. Functional magnetic resonance imaging (fMRI) performed one month later showed that brush-evoked activity in the brain demonstrates objective signal changes which correlate with perceptual changes in the phantom hand. This finding in humans corresponds to the observations of immediate plasticity in cortical pathways described in animals, including primates. The results suggest that reorganization of sensory pathways occurs very soon after amputation in humans, potentially due to the unmasking of ordinarily silent inputs rather than sprouting of new axon terminals.

Adult↗
PubMed1998

Psychophysical evidence for boundary and surface systems in human vision.

Psychophysical evidence is given for the existence of two distinct systems in human vision: a fast, sign-invariant system concerned with extracting contours and a slower, sign-sensitive system concerned with assigning surface color. A class of stimuli we developed seems to selectively activate the fast, contour system. This stimulus is formed by adjacent fields of black and white spots, which flicker in counterphase at 15 Hz, on a uniform gray field. Although subjects can not discriminate the temporal phase relationship between the fields of spots, they can, nevertheless see a "Phantom Contour" separating the two indiscriminable fields. The surface characteristics (temporal phase relationship of the spots) can only be seen when the stimulus is significantly slower (flicker < 7 Hz). In addition, phantom contours disappear with equiluminant spots but can be seen with very low contrast spots (< 10% contrast), and are enhanced with peripheral viewing. Taken together, the results suggest that the fast contour-extracting system may be the magnocellular system or a magno-recipient area. Implications for a stimulus which could isolate a contour extracting system, or a magno-recipient area are discussed.

Color Perception↗
PubMed1998

The neurology and evolution of humor, laughter, and smiling: the false alarm theory.

Laughter (and humor) involves the gradual build-up of expectation (a model) followed by a sudden twist or anomaly that entails a change in the model--but only as long as the new model is non-threatening--so that there is a deflation of expectation. The loud explosive sound is produced, we suggest, to inform conspecifics that there has been a 'false alarm', to which they need not orient. The same logic may underlie tickling (menacing approach followed by a light non-threatening contact). Thus tickling may serve as 'play', a rehearsal for adult laughter. And lastly, when one primate encounters another, he may have always begun with a threat gesture--to bare his canines--but upon recognizing the individual as kin he may stop the grimace halfway and 'smile'. When the insular cortex is damaged, patients giggle in response to pain, presumably because they can still sense the pain ('danger') but the pain is no longer aversive ('false alarm'), thereby fulfilling the two key requirements for laughter.

Biological Evolution↗
PubMed1998

The perception of phantom limbs. The D. O. Hebb lecture.

Almost everyone who has a limb amputated will experience a phantom limb--the vivid impression that the limb is not only still present, but in some cases, painful. There is now a wealth of empirical evidence demonstrating changes in cortical topography in primates following deafferentation or amputation, and this review will attempt to relate these in a systematic way to the clinical phenomenology of phantom limbs. With the advent of non-invasive imaging techniques such as MEG (magnetoencephalogram) and functional MRI, topographical reorganization can also be demonstrated in humans, so that it is now possible to track perceptual changes and changes in cortical topography in individual patients. We suggest, therefore, that these patients provide a valuable opportunity not only for exploring neural plasticity in the adult human brain but also for understanding the relationship between the activity of sensory neurons and conscious experience. We conclude with a theory of phantom limbs, some striking demonstrations of phantoms induced in normal subjects, and some remarks about the relevance of these phenomena to the question of how the brain constructs a 'body image.'

Adult↗
PubMed1997

Mirror agnosia.

Normal people rarely confuse the mirror image of an object with a real object so long as they realize they are looking into a mirror. We report a new neurological sign, 'mirror agnosia', following right parietal lesions in which this ability is severely compromised. We studied four right hemisphere stroke patients who had left visual field 'neglect'. i.e. they were indifferent to objects in their left visual field even though they were not blind. We then placed a vertical parasagittal mirror on each patients' right so that they could clearly see the reflection of objects placed in the (neglected) visual field. When shown a candy or pen on their left, the patients kept banging their hand into the mirror or groped behind it attempting to grab the reflection; they did not reach for the real object on the left, even though they were mentally quite lucid and knew they were looking into a mirror. Remarkably, all four patients kept complaining that the object was 'in the mirror', 'outside my reach' or 'behind the mirror'. Thus, even the patients' ability to make simple logical inferences about mirrors has been selectively warped to accommodate the strange new sensory world that they now inhabit. The finding may have implications for understanding how the brain creates representations of mirror reflections.

Aged↗