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Biomedical subjects

R Hari

Publications and source records attributed to R Hari.

At least 217 records · Page 12Linked to original sources
PubMed1983

Brainstem auditory-evoked potentials in progressive myoclonus epilepsy without Lafora bodies.

We studied brainstem auditory-evoked potentials of 11 patients suffering from the Finnish type of progressive myoclonus epilepsy (without Lafora bodies). All patients were ambulatory and had regular antiepileptic medication. The responses of 5 patients were interpreted as totally normal. In 6 cases there were slight deformations of the wave forms or of the amplitudes of the responses. The central conduction time of all patients was within the +/- 2 S.D. limits of the normal values. Postauricular muscular responses were not more prominent in patients than in controls. The results indicate that there is not any significant dysfunction in the cholinergic auditory pathways of the brainstem of these patients.

Adolescent↗
PubMed1983

Neuromagnetic responses from the second somatosensory cortex in man.

Cerebral magnetic fields elicited by electric stimulation of peripheral nerves were studied in man. Responses were found over the Sylvian fissure at latencies of 95-125 ms for both contra- and ipsilateral stimuli. The field distribution indicated that the responses are generated in the second somatosensory cortex SII at the upper bank of the Sylvian fissure. These responses seem to provide the first non-invasive tool to study the function of SII in man.

Adult↗
PubMed1983

Cerebral magnetic fields preceding self-paced plantar flexions of the foot.

Cerebral magnetic fields preceding self-paced plantar flexions of the feet were studied with a SQUID gradiometer in 4 subjects. A slow magnetoencephalographic (MEG) shift was observed to begin as early as 1 sec before the movement. The shift changed its polarity between frontal and parietal areas. The MEG shifts preceding right and left foot movements were similar in shape, but their polarities differed at many recording locations. Simultaneous movements of both feet were preceded by shifts approximately equal to the sum of the shifts preceding the unilateral foot movements at the same recording location. The results suggest that the EEG and MEG shifts preceding foot movements are largely generated by tangential current sources on the mesial surface of the contralateral hemisphere around the motor representation area of the foot.

Brain↗
PubMed1983

Slow EEG potentials preceding self-paced plantar flexions of hand and foot.

Slow EEG shifts preceding voluntary self-paced plantar flexions of hand and foot were studied in five healthy right handed subjects. The EEG was recorded from a coronal electrode chain at the central areas. The movements were preceded by slow negative shifts beginning even as early as one second before the movement and culminating in fast slopes during the early EMG activity at the onset of the movements. The EEG shifts preceding hand and foot movements were differently distributed over the scalp: hand movements were preceded by contralaterally maximal shifts a few hundred milliseconds before the movement, whereas the potential distribution preceding foot movements were symmetrical or ipsilaterally dominant. It is suggested that the differences in the scalp distributions are due to the different orientation of the current dipoles at the cortical motor areas of hand and foot.

Adult↗
PubMed1982

Interstimulus interval dependence of the auditory vertex response and its magnetic counterpart: implications for their neural generation.

Auditory vertex responses elicited by short tone bursts were compared with their magnetic counter parts. Special attention was paid to the behaviour of the N100 deflection of the response. Electrical responses were recorded from scalp locations Fp2, Fz, Cz, Pz, C4 and T4 and the magnetic responses half way between P4 and T6, at a point where the response has one of its amplitude extrema. Different ISIs (from 1 to 16 sec) were applied in order to differentiate specific and nonspecific evoked potential components from each other. The main results were as follows: (1) The scalp distsribution of the electical vertex response depends on the ISI used: with frequent stimulation there are no marked differences in the amplitudes of N100 between frontal and central areas but with long ISIs the amplitude maxima move to the vertex. (2) The magnetic responses also show a clear ISI dependence. The magnetic counterpart of N100 saturates at shorter ISIs than N100 recorded from the vertex. Independent of the ISI the magnetic counterpart of P200 is constantly very small. On the basis of the different sensitivities of the EEG and MEG to current sources of different orientations it is concluded that the auditory vertex response contains both modality specific and non-specific components. Experimental conditions, especially the ISI used, determine the relative contributions of these components to the potential recorded on the scalp.

Adult↗
PubMed1980

Evoked potentials elicited by long vibrotactile stimuli in the human EEG.

Evoked potentials elicited by long vibrotactile stimuli were studied in six subjects. Stimuli were vibratory bursts (60 HZ, 600 ms, 680 micrometers) delivered to the back of the hand trains of four stimuli with an interstimulus-interval of 2 s. Stimulus trains were repeated once every minute. EEG was recorded from vertex and from ipsi- and contralateral parietal areas. First stimuli of the trains elicited a transient response followed by a large negative sustained potential which reached its peak amplitude about 700 ms after the stimulus onset and which was not restricted to the stimulus duration. The negative component of the transient on-response as well as the sustained potential was at the 1st stimulus of the train maximal in amplitude at the vertex, and no significant difference between the ipsi- and contralateral parietal areas was detected. Stimulus repetition in the train resulted in a marked decrease of the transient response, and in an almost complete disappearance of the sustained potential, which was only occasionally observed during repeated stimuli.

Dominance, Cerebral↗
PubMed1979

Auditory evoked transient and sustained potentials in the human EEG: I. Effects of expectation of stimuli.

The characteristics of auditory evoked transient and sustained potentials were recorded using trains of four-tone stimuli of 1-second duration (interstimulus interval = 1 second) presented once every minute. The subject either attentively expected the stimuli or ignored them while reading. The electroencephalogram was recorded from derivations Cz-Al and Fz-Al. Expectation of the stimuli was associated with increased amplitudes of the transient responses both at the first stimulus of the train and during stimulus repetition. In contrast, the sustained potential at the first stimulus of the train was unchanged or smaller when the subject expected the stimuli. During stimulus repetition, however, the amplitude of the potential was enhanced by expectation of the stimuli. The results support the hypothesis of two sustained potential components and stress the importance of stimulus repetition rate when sustained potentials are studied.

Acoustic Stimulation↗
PubMed1979

Auditory evoked transient and sustained potentials in the human EEG: II. Effects of small doses of ethanol.

The effect of small doses of ethanol (0.4 g/kg) on auditory evoked transient and sustained potentials was studied. Tones of 1-second duration were presented in trains of four stimuli (interstimulus interval = 1 second; intertrain interval = 1 minute). The electroencephalogram was recorded from derivation Cz-Al. Ethanol depressed the transient responses both at the first stimulus of the train and during repeated stimuli. The sustained potentials elicited by the first stimuli of the train were not affected by ethanol, whereas the sustained potentials elicited by repeated stimuli were larger in amplitude under the influence of ethanol than during control experiments. It is suggested that the decrease of the transient responses under the influence of ethanol is mainly due to depression of the reticular formation, whereas the increase of sustained potentials reflects ethanol-induced release of intracortical inhibition.

Acoustic Stimulation↗
PubMed1979

Biphasic effects of ethanol on behavioral and electrophysiological parameters can be explained by functional organization of neural networks.

The biphasic effect of ethanol on the CNS is usually explained by assuming that excitatory and depressant effects are mediated by different mechanisms. The present alternative explanation states that ethanol depresses the activity of all neurons to the same extent, but that the biphasic effect can result from the functional organization of the neural network concerned. Current experimental evidence is in accordance with both explanations.

Behavior↗
PubMed1978

Effect of stimulus repetition on negative sustained potentials elicited by auditory and visual stimuli in the human EEG.

Effect of repetition of auditory and visual stimuli on sensory-evoked sustained potentials was studied. The stimuli were tones and flashes of 1 sec duration presented in trains of six stimuli with an inter-stimulus-interval of 1 sec. The repetition rate of the trains was 1 train/min. The EEG was recorded from electrodes located at Cz, Pz and Oz. Both auditory and visual stimuli elicited negative sustained potentials which during the first stimuli of the trains were maximal in amplitude and shortest in latency at Cz. Repetition of the stimulus resulted in almost complete disappearance of the sustained potentials; for auditory stimulation a small negative shift was recorded only at Cz, whereas for visual stimulation a small sustained potential was seen only at Pz and Oz. The results indicate that the slow potentials evoked by short tones or lights are composed of at least two components. One of these components may reflect neural processing associated with orienting reflex. The other component seems to be related to specific neural processing of the stimulus.

Acoustic Stimulation↗