Biomedical subjects

R B Govindan

Publications and source records attributed to R B Govindan.

4 recordsLinked to original sources

PubMed2006

Time delay and partial coherence analyses to identify cortical connectivities.

Recently it has been demonstrated by Albo that partial coherence analysis is sensitive to signal to noise ratio (SNR) and that it will always identify the signal with the highest SNR among the three signals as the main (driving) influence. We propose to use time delay analysis in parallel to partial coherence analysis to identify the connectivities between the multivariate time series. Both are applied to a theoretical model (used by Albo) to analyse the connections introduced in the model. Time delay analysis identifies the connections correctly. We also apply these analyses to the electroencephalogram (EEG) and electromyogram of essential tremor patients and EEG of normal subjects while bimanually tapping their index fingers. Biologically plausible cortico-muscular and cortico-cortical connections are identified by these methods.

Algorithms↗

PubMed2005

Parkinsonian action tremor: interference with object manipulation and lacking levodopa response.

It has been postulated that Parkinsonian action tremor is distinct from classical resting tremor and that it may contribute to a loss of manual dexterity in Parkinson's disease. We analyzed pinch grip coordination in 20 patients with Parkinson's disease. An object with and without an additional 500 g weight was grasped, lifted and held for a short time with opposed thumb and index finger. Force sensors recorded the force exerted by both fingers. Spectral analysis of the force traces was performed. Transition times between grasping and lifting the object were measured. 18 age matched normal volunteers served as a control group. While holding the object, there were force oscillations in the 3.5-6.5 Hz band indicating (reemerging) classical Parkinsonian tremor in 65% of the patients. This was reduced to 15-20% under levodopa. Oscillations in the 6-15 Hz band were found in 30% (50% with weight) of the patients, remaining unchanged under levodopa, and in 10% (20% with weight) of the normal controls. During lift initiation, 6-15 Hz oscillations were found in all patients and the majority of controls. The band power was positively correlated with the movement transition times in the severely akinetic patients and was significantly higher than in controls. It remained unchanged under levodopa. Our data confirm that Parkinsonian action tremor activated during complex voluntary movements is distinct from classical resting tremor. It does not show a clear levodopa response but affects dextrous movement coordination when associated with clinically severe overall akinesia.

Adult↗

PubMed2004

Two different pathogenetic mechanisms in psychogenic tremor.

BACKGROUND: The pathophysiologic mechanism underlying psychogenic tremor is not clear. Continuous voluntary production of tremor may be uncovered by a positive entrainment of tremor in different limbs. But some patients have tremor ongoing during their waking time which is unlikely to be produced voluntarily. Therefore, nonvoluntary physiologic oscillatory mechanisms must be considered. METHODS: Fifteen patients with psychogenic tremor manifesting in both hands, who were diagnosed using established criteria, were examined. Postural tremor was recorded with accelerometry and electromyography (EMG) while the hands were held against gravity. Power spectral peak frequencies and accelerometric total power as a measure of amplitude were determined. Coherency spectra between the EMG signals from the right and left arm were calculated. RESULTS: Seven of 15 patients showed a significant coherency between the two hands; the remaining 8 patients maintained independent oscillations. Clinical presentation, tremor frequencies, and amplitudes were not significantly different between the two groups. CONCLUSIONS: Two different pathogenetic mechanisms may play a role in psychogenic tremor. Bilateral voluntary movements are typically coherent. Thus, coherent psychogenic tremor would be in keeping with voluntarily produced oscillations. Absent coherence is an indication of another, possibly nonvoluntary mechanism like clonus or enhanced physiologic tremor.

Adult↗

PubMed2002

Global climate models violate scaling of the observed atmospheric variability.

We test the scaling performance of seven leading global climate models by using detrended fluctuation analysis. We analyze temperature records of six representative sites around the globe simulated by the models, for two different scenarios: (i) with greenhouse gas forcing only and (ii) with greenhouse gas plus aerosol forcing. We find that the simulated records for both scenarios fail to reproduce the universal scaling behavior of the observed records and display wide performance differences. The deviations from the scaling behavior are more pronounced in the first scenario, where also the trends are clearly overestimated.

Journal Article↗