Biomedical subjects

R Hari

Publications and source records attributed to R Hari.

At least 19 recordsLinked to original sources

PubMed2006

The imprint of action: motor cortex involvement in visual perception of handwritten letters.

Humans are able to recognize handwritten texts accurately despite the extreme variability of scripts from one writer to another. This skill has been suggested to rely on the observer's own knowledge about implicit motor rules involved in writing. To investigate the possible neural correlates of such an ability, we monitored with magnetoencephalography (MEG) the approximately 20-Hz oscillations originating from the motor cortex. The oscillations were more suppressed after visual presentation of handwritten than printed letters, indicating stronger excitation of the motor cortex to handwritten scripts. These results support the idea of embodied visual perception of handwritten scripts and the involvement of the motor cortex in the underlying action-perception link.

Adult↗

PubMed2006

Neuromagnetic responses to vowels vs. tones reveal hemispheric lateralization.

OBJECTIVE: To evaluate whether a simple auditory paradigm could demonstrate a difference in cortical lateralization between right- and left-handed subjects. Such information would be important for later development of clinical noninvasive tests of hemispheric language dominance in candidates for brain surgery. METHODS: Healthy subjects (10 strongly right-handed, 10 strongly left-handed, 5 weakly right-handed, and two ambidextrous) listened to binaural pairs of tones and pairs of Finnish vowels and decided whether the items in the pair were the same (target probability 20%). Cortical responses were recorded with whole-scalp magnetoencephalography. RESULTS: The laterality index for strengths of the auditory-cortex 100 ms responses (N100m) to vowels vs. tones suggested left-hemispheric dominance in 8 of the 10 strongly right-handed subjects, and right-hemispheric dominance in 7 of the 10 left-handed subjects. CONCLUSIONS: Our results demonstrate difference in hemispheric dominance for processing of vowels between right-handed and left-handed subjects. This difference resembles language lateralization suggested by previous invasive studies as well as by anatomical and functional comparisons in left- and right-handed subjects. SIGNIFICANCE: After comparison with the Wada test, this simple paradigm could prove useful as a noninvasive test for language lateralization in clinical settings.

Acoustic Stimulation↗

PubMed2005

On the human sensorimotor-cortex beta rhythm: sources and modeling.

Cortical oscillations in the beta band (13-35 Hz) are known to be modulated by the GABAergic agonist benzodiazepine. To investigate the mechanisms generating the approximately 20-Hz oscillations in the human cortex, we administered benzodiazepines to healthy adults and monitored cortical oscillatory activity by means of magnetoencephalography. Benzodiazepine increased the power and decreased the frequency of beta oscillations over rolandic areas. Minimum current estimates indicated the effect to take place around the hand area of the primary sensorimotor cortex. Given that previous research has identified sources of the beta rhythm in the motor cortex, our results suggest that these same motor-cortex beta sources are modulated by benzodiazepine. To explore the mechanisms underlying the increase in beta power with GABAergic inhibition, we simulated a conductance-based neuronal network comprising excitatory and inhibitory neurons. The model accounts for the increase in the beta power, the widening of the spectral peak, and the slowing down of the rhythms with benzodiazepines, implemented as an increase in GABAergic conductance. We found that an increase in IPSCs onto inhibitory neurons was more important for generating neuronal synchronization in the beta band than an increase in IPSCs onto excitatory pyramidal cells.

Adult↗

PubMed2004

Chlamydia trachomatis genital infection in apparently healthy adult population of Tamil Nadu, India: a population-based study.

Since the epidemiology of Chlamydia trachomatis infection in apparently healthy population has not been studied in India, a population-based study was conducted in the state of Tamil Nadu, India in order to analyse the prevalence of genital chlamydial infections in the community and to implement control programmes. A representative sample was taken from three randomly selected districts by using the 'probability proportional to size' cluster survey method. Households were the basic units of clusters. Adults aged 15-45 years, pre-identified from the selected households were enrolled during the medical camps conducted for a major study on community prevalence of sexually transmitted diseases in Tamil Nadu. Blood and urine samples collected from the study subjects were tested by enzyme-linked immunosorbent assay (ELISA) for anti-chlamydial IgM antibodies and by the commercial Amplicor polymerase chain reaction (PCR) test for chlamydial DNA. The prevalence of anti-C. trachomatis antibodies determined by IgM-ELISA was 2.4% (95% CI 1.6%-3.2%). The prevalence of genital chlamydial infection determined by PCR was 1.1% (95% CI 0.5%-1.7%). Majority of the detected infections (68.8%) were asymptomatic. This is the first Indian report on the prevalence of genital chlamydial infections in the general population. It is concluded that this study provides evidence for a substantial burden of approximately 10 million asymptomatic genital chlamydial infection cases in the sexually active age groups in the general population of India.

Adolescent↗

PubMed2003

Dorsal penile nerve stimulation elicits left-hemisphere dominant activation in the second somatosensory cortex.

Activation of peripheral mixed and cutaneous nerves activates a distributed cortical network including the second somatosensory cortex (SII) in the parietal operculum. SII activation has not been previously reported in the stimulation of the dorsal penile nerve (DPN). We recorded somatosensory evoked fields (SEFs) to DPN stimulation from 7 healthy adults with a 122-channel whole-scalp neuromagnetometer. Electrical pulses were applied once every 0.5 or 1.5 sec to the left and right DPN. For comparison, left and right median and tibial nerves were stimulated alternatingly at 1.5-sec intervals. DPN stimuli elicited weak, early responses in the vicinity of responses to tibial nerve stimulation in the primary somatosensory cortex. Strong later responses, peaking at 107-126 msec were evoked in the SII cortices of both hemispheres, with left-hemisphere dominance. In addition to tactile processing, SII could also contribute to mediating emotional effects of DPN stimuli.

Adult↗

PubMed2003

Task-dependent modulations of cortical oscillatory activity in human subjects during a bimanual precision grip task.

Oscillations are a widespread feature of normal brain activity and have been reported at a variety of different frequencies in different neuronal systems. The demonstration that oscillatory activity is present in motor command signals has prompted renewed interest in the possible functions of synchronous oscillatory activity within the primate sensorimotor system. In the current study, we investigated task-dependent modulations in coupling between sensorimotor cortical oscillators during a bimanual precision grip task. The task required a hold-ramp-hold pattern of grip force to be exerted on a compliant object with the dominant right hand, while maintaining a steady grip with the nondominant hand. We found significant task-related modulation of 15- to 30-Hz coherence between magnetoencephalographic (MEG) activity recorded from the left sensorimotor cortex and electromyographic (EMG) activity in hand muscles on the right side. This coherence was maximal during steady hold, but disappeared during the ramp movements. Interestingly coherence between the right sensorimotor MEG and left-hand EMG showed a similar, although less deeply modulated, task-related pattern, even though this hand was maintaining a simple steady grip. No significant ipsilateral MEG-EMG coherence was observed in the 15- to 30-Hz passband for either hand. These results suggest that the cortical oscillators in the two sensorimotor cortices are independent to some degree but that they may share a common mechanism that attenuates the cortical power in both hemispheres in the 15- to 30-Hz range during movements of one hand. The results are consistent with the hypothesis that oscillatory activity in the motor system is important in resetting the descending motor commands needed for changes in motor state, such as those that occur in the transition from movement to steady grip.

Adult↗

PubMed2003

Activation of the human posterior parietal and temporoparietal cortices during audiotactile interaction.

We recorded cortical-evoked responses with a whole-scalp neuromagnetometer to study human brain dynamics associated with audiotactile interaction. The subjects received unilateral auditory (A) or tactile (T) stimuli, or both stimuli simultaneously (AT), alternating to the left and right side. Responses to AT stimuli differed significantly from the algebraic sum of responses to A and T stimuli (A + T) at 75-85 and 105-130 ms and indicated suppressive audiotactile interaction. Source modeling revealed that the earlier interaction occurred in the contralateral posterior parietal cortex and the later interaction in the contralateral parietal opercula between the SII cortex and the auditory cortex. The interaction was significantly stronger in the left than the right hemisphere. In most subjects, AT responses were far more similar to T than to A responses, suggesting suppression of auditory processing during the spatially and temporally concordant audiotactile stimuli in which the tactile component was subjectively more salient.

Acoustic Stimulation↗

PubMed2002

Magnetoencephalographic correlates of audiotactile interaction.

To seek for correlates of an interaction between auditory and somatosensory processing, the brain's magnetic field in response to simultaneously presented auditory (A) and tactile (T) stimuli was compared with the sum of the respective unimodal responses (A+T). The stimuli were binaural 1047-Hz tone bursts of 60 dB sensation level and tactile pressure pulses to the right thumb. The mean interval between two stimuli of the same modality was 1.95 s. The magnetic field was recorded using a 306-channel whole-scalp neuromagnetometer. A clear audiotactile interaction was revealed in the hemisphere contralateral to the side of tactile stimulation in six of eight subjects, whereas in the ipsilateral hemisphere an interaction was noticed in only three subjects. The time courses of these audiotactile interaction fields typically showed major deflections of opposite polarities around 140 and 220 ms. The first deflection appeared to arise in the region of the secondary somatosensory cortex (SII). The polarity of this interaction was consistent with the view that the auditory stimulus resulted in a partial inhibition in SII. In two subjects, strong indications of auditory contributions to the interaction were available, although in different hemispheres. The relatively high interindividual variability of the observed interaction, which represents potential neural substrates for multisensory integration, could indicate that the way subjects perceive the simultaneous presentation of auditory and tactile stimuli differs.

Attention↗

PubMed2002

Cortical activation associated with passive movements of the human index finger: an MEG study.

We recorded somatosensory evoked fields to passive extensions of the left and right index fingers in eight healthy adults. A new nonmagnetic device was designed to produce calibrated extensions of 19 degrees, with a mean angular velocity of 630 degrees/s. The responses, recorded with a 306-channel neuromagnetometer, were modeled with current dipoles. The earliest activation was in the primary somatosensory cortex, with peaks at 36-58 and 30-82 ms for left and right index finger extensions, respectively. Later signals were observed in the left second somatosensory (SII) cortex in six of eight subjects at 75-175 and 75-155 ms for left- and right-sided extensions, respectively; three subjects showed bilateral SII activation in at least one condition. Our results suggest a predominant role for the human left SII cortex in proprioceptive processing.

Adult↗

PubMed2002

Oscillatory cortical drive to isometrically contracting muscle in Unverricht-Lundborg type progressive myoclonus epilepsy (ULD).

OBJECTIVE: We investigated with whole-scalp magnetoencephalography (MEG) oscillatory cortical drive to isometrically contracting muscle in 8 genetically verified, and thus etiologically homogeneous, Unverricht-Lundborg type progressive myoclonus epilepsy (ULD) patients suffering from cortical myoclonus and generalized tonic-clonic seizures. The results were compared with those of 8 healthy control subjects. METHODS: Cortical MEG signals were measured simultaneously with surface electromyography (EMG) during isometric contraction of the left and right first dorsal interosseus muscles. Cortex-muscle coherence and cross-correlograms between MEG and EMG signals were calculated as indicators of oscillatory cortical drive to muscle. The cortical areas involved in the maximum cortex-muscle coherence were also identified. RESULTS: In patients, the strengths of the dominant coherent peaks were 2-4 fold compared with the healthy controls. Whereas the coherence was found strictly in the contralateral primary motor cortex in controls, additional coherent activity was observed ipsilaterally in 5 out of 8 patients. CONCLUSIONS: The remarkably increased MEG-EMG coherence in ULD patients suggests altered oscillatory cortical drive to the muscle during isometric contraction. We suggest that the enhanced cortex-muscle coherence in ULD patients reflects reduced inhibition in the motor cortex, and may contribute to disturbed voluntary movements.

Adolescent↗

PubMed2002

Herbal medicines for liver diseases in India.

The use of natural remedies for the treatment of liver diseases has a long history, starting with the Ayurvedhic treatment, and extending to the Chinese, European and other systems of traditional medicines. The 21st century has seen a paradigm shift towards therapeutic evaluation of herbal products in liver diseases by carefully synergizing the strengths of the traditional systems of medicine with that of the modern concept of evidence-based medicinal evaluation, standardization of herbal products and randomized placebo controlled clinical trials to support clinical efficacy. The present review provides the status report on the scientific approaches made to herbal preparations used in Indian systems of medicine for the treatment of liver diseases. In spite of the availability of more than 300 preparations for the treatment of jaundice and chronic liver diseases in Indian systems of medicine using more than 87 Indian medicinal plants, only four terrestrial plants have been scientifically elucidated while adhering to the internationally acceptable scientific protocols. In-depth studies have proved Sylibum marianum to be anti-oxidative, antilipidperoxidative, antifibrotic, anti-inflammatory, immunomodulating and liver regenerative. Glycyrrhiza glabra has been shown to be hepatoprotective and capable of inducing an indigenous interferon. Picrorhiza kurroa is proved to be anti-inflammatory, hepatoprotective and immunomodulatory. Extensive studies on Phyllanthus amarus have confirmed this plant preparation as being anti-viral against hepatitis B and C viruses, hepatoprotective and immunomodulating, as well as possessing anti-inflammatory properties. For the first time in the Indian systems of medicine, a chemo-biological fingerprinting methodology for standardization of P. amarus preparation has been patented.

Humans↗

PubMed2002

Facilitation of neonatal nasotracheal intubation with premedication: a randomized controlled trial.

OBJECTIVES: To determine if premedication reduces the time and number of attempts by junior medical staff to achieve nasotracheal intubation in neonates. The experimental design was a non-blinded randomized controlled pilot trial. The setting was a perinatal centre in a university teaching hospital. METHODS: Twenty infants (within the ranges of 25-40 weeks gestation, 650-3660 g and 1 h to 81 days of age) requiring semi-urgent intubation were randomized to either premedication with morphine, atropine and suxamethonium, or to awake intubation. RESULTS: There were no significant differences between the two groups in regard to prior intubation experience of the staff or infant weight or gestation. The intubation procedure, including intervening events, to completion was significantly faster in premedicated infants (median 60 s vs 595 s; P = 0.002) who were intubated at a younger postnatal age. It took twice as many attempts to intubate a conscious infant (median 2 vs 1; P = 0.010). There was a greater decrease in heart rate from the baseline in the unpremedicated group (mean 68 b.p.m. vs 29 b.p.m.; P = 0.017), but decreases in oxygen saturation were not different. Blood was observed in the oral and nasal passages after intubation in five of the awake infants and in one of the premedicated infants. CONCLUSIONS: The use of premedication reduces the total time and number of attempts taken to achieve successful nasotracheal intubation of neonates by junior medical staff under supervision.

Analgesics, Opioid↗

PubMed2002

Whose arm is it anyway? An fMRI case study of supernumerary phantom limb.

Under normal circumstances, information from a number of sources is combined to compute a unitary percept of the body. However, after pathology these influences may be perceived simultaneously, resulting in multiple dissociated conscious representations. In a recent paper, we described subject E.P., a right-handed female stroke patient with a right frontomesial lesion who sporadically experiences a supernumerary 'ghost' left arm that occupies the previous position of the real left arm after a delay of 60-90 s. We used a delayed response paradigm with functional MRI to examine the haemodynamic correlates of E.P.'s illusion. Comparison of periods of time during scanning when the ghost arm was present against when it was not revealed a single cluster (9 voxels, t = 5.11, P < 0.012 corrected for multiple comparisons) located on the right medial wall in the supplementary motor area ('SMA proper'). Our results suggest that areas traditionally classified as part of the motor system can influence the conscious perception of the body. We propose that, as a consequence of her injury, E.P. is aware of the position of the phantom limb in this 'action space' while also continuing to be aware of the true position of her real limb on the basis of afferent somatosensory information.

Adult↗

PubMed2001

Stronger reactivity of the human primary motor cortex during observation of live rather than video motor acts.

The monkey premotor cortex contains neurons that are activated both when the monkey performs motor acts and when he observes actions made by others. A similar mirror neuron system, involving several brain areas, has been found in humans. We recorded neuromagnetic oscillatory activity from the primary motor cortex of 10 healthy subjects when they observed live and videotaped finger movements. The left and right median nerves were stimulated alternatingly and the poststimulus level of the approximately 20 Hz rhythm was quantified. Compared with the rest condition, the approximately 20 Hz rhythm was dampened 15-19% more when the subjects observed live rather than videotaped hand movements, indicating stronger activation of the primary motor cortex. These results suggest that the human mirror neuron system differentiates natural and artificially presented movements.

Adult↗

PubMed2001

Coinciding early activation of the human primary visual cortex and anteromedial cuneus.

Proper understanding of processes underlying visual perception requires information on the activation order of distinct brain areas. We measured dynamics of cortical signals with magnetoencephalography while human subjects viewed stimuli at four visual quadrants. The signals were analyzed with minimum current estimates at the individual and group level. Activation emerged 55-70 ms after stimulus onset both in the primary posterior visual areas and in the anteromedial part of the cuneus. Other cortical areas were active after this initial dual activation. Comparison of data between species suggests that the anteromedial cuneus either comprises a homologue of the monkey area V6 or is an area unique to humans. Our results show that visual stimuli activate two cortical areas right from the beginning of the cortical response. The anteromedial cuneus has the temporal position needed to interact with the primary visual cortex V1 and thereby to modify information transferred via V1 to extrastriate cortices.

Adult↗

PubMed2001

Three-dimensional integration of brain anatomy and function to facilitate intraoperative navigation around the sensorimotor strip.

We studied 12 patients with brain tumors in the vicinity of the sensorimotor region to provide a preoperative three-dimensional visualization of the functional anatomy of the rolandic cortex. We also evaluated the role of cortex-muscle coherence analysis and anatomical landmarks in identifying the sensorimotor cortex. The functional landmarks were based on neuromagnetic recordings with a whole-scalp magnetometer, coregistred with magnetic resonance images. Evoked fields to median and tibial nerve and lip stimuli were recorded to identify hand, foot and face representations in the somatosensory cortex. Oscillatory cortical activity, coherent with surface electromyogram during isometric muscle contraction, was analyzed to reveal the hand and foot representations in the precentral motor cortex. The central sulcus was identified also by available anatomical landmarks. The source locations, calculated from the neuromagnetic data, were displayed on 3-D surface reconstructions of the individual brains, including the veins. The preoperative data were verified during awake craniotomy by cortical stimulation in 7 patients and by cortical somatosensory evoked potentials in 5 patients. Sources of somatosensory evoked fields identified correctly the postcentral gyrus in all patients. Useful corroborative information was obtained from anatomical landmarks in 11 patients and from cortex-muscle correlograms in 8 patients. The preoperative visualization of the functional anatomy of the sensorimotor strip assisted in designing the operational strategy, facilitated orientation of the neurosurgeon during the operation, and speeded up the selection of sites for intraoperative stimulation or mapping, thereby helping to prevent damage of eloquent brain areas during surgery.

Adult↗

PubMed2001

Sustained activation of the human SII cortices by stimulus trains.

To compare the functional properties of neurons in the human primary (SI) and secondary (SII) cortices, we recorded somatosensory-evoked fields (SEFs) from seven healthy subjects to single electric stimuli and stimulus trains delivered to the median nerve at 8--12 Hz. The SI and SII cortices responded strikingly differently to stimulus trains: whereas SI followed each stimulus with a sharp transient response up to at least 12 Hz, the transient responses were much less prominent at SII, which mainly responded with a sustained field that returned to base level at 800--1000 ms. The different response patterns of SI and SII suggest that the inhibition, following the early excitatory responses, is weaker at SII than SI, or that inhibitory responses of these two areas differ in their relative timing.

Adult↗

PubMed2001

Evidence for a 7- to 9-Hz "sigma" rhythm in the human SII cortex.

Electrical activity of the human brain features several rhythmical components which can be readily studied with whole-scalp neuromagnetometers. We describe a new 7- to 9-Hz "sigma" rhythm in the human second somatosensory cortex, distinct from both the mu rhythm of the primary sensorimotor cortex and the tau rhythm of the supratemporal auditory cortex. Sigma shows rate-selective responsiveness to rhythmical median nerve stimulation and is enhanced by stimulation at the rhythm's dominant frequency. Single stimuli may trigger several periods of the rhythm. The functional significance of the sigma rhythm remains to be investigated.

Adult↗