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Biomedical subjects

P G Ray

Publications and source records attributed to P G Ray.

At least 19 recordsLinked to original sources
PubMed2005

Cognitive and behavioral effects of lamotrigine and topiramate in healthy volunteers.

BACKGROUND: The relative cognitive and behavioral effects of lamotrigine (LTG) and topiramate (TPM) are unclear. METHODS: The authors directly compared the cognitive and behavioral effects of LTG and TPM in 47 healthy adults using a double-blind, randomized crossover design with two 12-week treatment periods. During each treatment condition, subjects were titrated to receive either LTG or TPM at a target dose of 300 mg/day for each. Neuropsychological evaluation included 17 measures yielding 41 variables of cognitive function and subjective behavioral effects. Subjects were tested at the end of each antiepileptic drug (AED) treatment period and during two drug-free conditions (pretreatment baseline and 1 month following final AED withdrawal). RESULTS: Direct comparison of the two AEDs revealed significantly better performance on 33 (80%) variables for LTG, but none for TPM. Even after adjustment for blood levels, performance was better on 19 (46%) variables for LTG, but none for TPM. Differences spanned both objective cognitive and subjective behavioral measures. Comparison of TPM to the non-drug average revealed significantly better performance for non-drug average on 36 (88%) variables, but none for TPM. Comparison of LTG to non-drug average revealed better performance on 7 (17%) variables for non-drug average and 4 (10%) variables for LTG. CONCLUSIONS: Lamotrigine produces significantly fewer untoward cognitive and behavioral effects compared to topiramate (TPM) at the dosages, titrations, and timeframes employed in this study. The dosages employed may not have been equivalent in efficacy. Future studies are needed to delineate the cognitive and behavioral effects of TPM at lower dosages.

Adult↗
PubMed2004

An epidemic of rotavirus diarrhoea in Jawhar Taluk, Thane district, Maharashtra, India, December 2000-January 2001.

An epidemic of diarrhoea in Jawhar, a tribal area of Thane district, Maharashtra, India was investigated. Within a period of approximately 2 months 490 cases of acute diarrhoea were reported among children under 5 years of age, with a case fatality rate of 0.40%. Twenty-seven out of 39 (69.23%) rectal swabs/faecal specimens obtained from hospitalized paediatric patients up to 2 years of age from Jawhar were positive by ELISA for rotavirus. Of these, seven were in the age group of < or = 6 months. Seven ELISA-positive faecal specimens were positive for serotype G3 by RT PCR. Out of 15 serum samples collected from these patients, 12 showed the presence of rotavirus-specific IgM. Rotavirus appears to be the aetiological agent of this widespread outbreak in Jawhar, Thane district, Maharashtra state, India.

Adolescent↗
PubMed2002

Gamma coherence and conscious perception.

BACKGROUND: High-frequency (e.g., gamma 30 to 50 Hz) coherent neural activity has been postulated to underlie binding of independent neural assemblies and thus integrate processing across distributed neuronal networks to achieve a unified conscious experience. Prior studies suggest that gamma activity may play a role in perceptual mechanisms, but design limitations raise concerns. Thus, controversy exists as to the hypothesis that gamma activity is necessary for perceptual awareness. In addition, controversy exists as to whether the primary sensory cortices are involved directly in the mechanisms of conscious perception or just in processes prior to conscious awareness. OBJECTIVE: To investigate the relation of gamma coherence and perception. METHODS: Digital intracranial electrocorticographic recordings from implanted electrodes were obtained in six patients with intractable epilepsy during a simple somatosensory detection task for near-threshold stimuli applied to the contralateral hand. Signal analyses were then conducted using a quantitative approach that employed two-way Hanning digital bandpass filters to compute running correlations across pairs of channels at various time epochs for each patient and each perception state across multiple bandwidths. RESULTS: Gamma coherence occurs in the primary somatosensory cortex approximately 150 to 300 milliseconds after contralateral hand stimuli that are perceived, but not for nonperceived stimuli, which did not differ in character/intensity or early somatosensory evoked potentials. CONCLUSION: The results are consistent with the possible direct involvement of primary sensory cortex in elemental awareness and with a role for gamma coherence in conscious perception.

Adult↗
PubMed2001

Differential cognitive and behavioral effects of carbamazepine and lamotrigine.

BACKGROUND: The relative cognitive and behavioral effects of lamotrigine compared with the older standard antiepileptic drugs (AED) are uncertain. OBJECTIVE: To directly compare the cognitive and behavioral effects of carbamazepine and lamotrigine. METHODS: The cognitive and behavioral effects of carbamazepine and lamotrigine were assessed in 25 healthy adults using a double-blind, randomized crossover design with two 10-week treatment periods. During each treatment condition, subjects received either lamotrigine (150 mg/day) or carbamazepine (mean 696 mg/day) adjusted to a dose to achieve midrange standard therapeutic blood levels (mean 7.6 microg/mL). Subjects were tested at the end of each AED treatment period and in three drug-free conditions (two pretreatment baselines and a final posttreatment period [1 month after last AED]). The neuropsychological test battery included 19 measures yielding 40 total variables. RESULTS: Direct comparison of the two AED revealed significantly better performance on 19 (48%) variables for lamotrigine but none for carbamazepine. Differences spanned both objective cognitive and subjective behavioral measures, including cognitive speed, memory, graphomotor coding, neurotoxic symptoms, mood factors, sedation, perception of cognitive performance, and other quality-of-life perceptions. Comparison of carbamazepine with the nondrug average revealed significantly better performance for nondrug average on 24 (62%) variables but none for carbamazepine. Comparison of lamotrigine with nondrug average revealed better performance on one (2.5%) variable for nondrug average and on one (2.5%) variable for lamotrigine. CONCLUSION: Lamotrigine produces significantly fewer untoward cognitive and behavioral effects than carbamazepine at the dosages used in this study.

Adult↗
PubMed2001

Relationship of extinction to perceptual thresholds for single stimuli.

OBJECTIVE: To demonstrate the effects of target stimulus intensity on extinction to double simultaneous stimuli. BACKGROUND: Attentional deficits contribute to extinction in patients with brain lesions, but extinction (i.e., masking) can also be produced in healthy subjects. The relationship of extinction to perceptual thresholds for single stimuli remains uncertain. METHODS: Brief electrical pulses were applied simultaneously to the left and right index fingers of 16 healthy volunteers (8 young and 8 elderly adults) and 4 patients with right brain stroke (RBS). The stimulus to be perceived (i.e., target stimulus) was given at the lowest perceptual threshold to perceive any single stimulus (i.e., Minimal) and at the threshold to perceive 100% of single stimuli. The mask stimulus (i.e., stimulus given to block the target) was applied to the contralateral hand at intensities just below discomfort. RESULTS: Extinction was less for target stimuli at 100% than Minimal threshold for healthy subjects. Extinction of left targets was greater in patients with RBS than elderly control subjects. Left targets were extinguished less than right in healthy subjects. In contrast, the majority of left targets were extinguished in patients with RBS even when right mask intensity was reduced below right 100% threshold for single stimuli. RBS patients had less extinction for right targets despite having greater left mask - threshold difference than control subjects. In patients with RBS, right "targets" at 100% threshold extinguished left "masks" (20%) almost as frequently as left masks extinguished right targets (32%). CONCLUSIONS: Subtle changes in target intensity affect extinction in healthy adults. Asymmetries in mask and target intensities (relative to single-stimulus perceptual thresholds) affect extinction in RBS patients less for left targets but more for right targets as compared with control subjects.

Adult↗
PubMed2000

Train duration effects on perception: sensory deficit, neglect, and cerebral lateralization.

The mechanisms of conscious perception are uncertain. In a preliminary study, dramatic effects of train duration on perception in a patient with right brain stroke were noted. In this study, the mechanisms of train duration on perception of peripheral somatosensory stimuli are examined. Subjects included healthy adults and patients with right brain infarctions. Train duration effects on perception were examined in relation to cerebral infarction, handedness, age, elevated peripheral threshold via bupivacaine, and impaired attention via diazepam or scopolamine. Perceptual thresholds to electrical pulses on the hand decreased as train duration increased, but only over the first several hundred milliseconds. Compared to controls, right brain stroke patients showed much greater lowering of threshold in the affected hand as train duration was extended. Age and bupivacaine elevated thresholds, but had little or no influence on train duration effects. Diazepam and scopolamine had no effect on thresholds. Thresholds were lower in the left than right hand of healthy dextral subjects, irrespective of age. Sinistral subjects had less left/right asymmetry. Increased train duration effect in patients is not explained by a primary elevation in threshold or by impaired vigilance. Lower perceptual thresholds in the left hand of healthy dextral subjects is consistent with right cerebral dominance for externally directed attention.

Adjuvants, Anesthesia↗
PubMed1999

Physiology of perception: cortical stimulation and recording in humans.

OBJECTIVES: 1) To determine the effect of stimulus train duration (TD) on sensory perception using direct stimulation of somatosensory and visual cortices. 2) To investigate the occurrence of evoked potentials in response to stimulation that is subthreshold for perception. BACKGROUND: Studies of the mechanisms of conscious perception using direct cortical stimulation and recording techniques are rare. The clinical necessity to implant subdural electrode grids in epilepsy patients undergoing evaluation for surgery offers an opportunity to examine the role of stimulus parameters and evoked potentials in conscious perception. METHODS: Subjects included epilepsy patients with grids over somatosensory or occipital cortex. Single pulses (100 microseconds) and stimulus trains were applied to electrodes, and thresholds for perception were found. Evoked potentials were recorded in response to peripheral stimulation at intensities at, above, and below sensory threshold. RESULTS: During cortical stimulation, sensory threshold changed little for stimulus trains of 250 milliseconds and longer, but increased sharply as TD decreased below this level. Primary evoked activity was recorded in response to peripheral stimulations that were subthreshold for conscious perception. CONCLUSIONS: The results confirm a previous report of the effects of stimulus TD on sensory threshold. However, no motor responses occurred following somatosensory stimulation with short trains, as previously reported. The TD threshold pattern was similar in visual cortex. In agreement with the previous report, early components of the primary evoked response were not correlated with conscious sensory awareness.

Adolescent↗
PubMed1999

Differential cognitive effects of carbamazepine and gabapentin.

PURPOSE: The cognitive effects of the newer antiepileptic drugs (AEDs) compared with the older standard AEDs are uncertain. METHODS: We directly compared the cognitive effects of carbamazepine (CBZ) and gabapentin (GBP) in 35 healthy subjects by using a double-blind, randomized crossover design with two 5-week treatment periods. During each treatment condition, subjects received either GBP, 2,400 mg/day, or CBZ (mean, 731 mg/day) adjusted to a dose to achieve midrange standard therapeutic blood levels (mean, 8.3 microg/ml). Subjects were tested at the end of each AED treatment period and in four drug-free conditions [two pretreatment baselines and two post-treatment washout periods (1 month after each AED)]. The neuropsychological test battery included 17 measures yielding 31 total variables. RESULTS: Direct comparison of the two AEDs revealed significantly better performance on eight variables for GBP, but none for CBZ. Comparison of CBZ and GBP to the nondrug average revealed significant statistical differences for 15 (48%) of 31 the variables. Pairwise follow-up analyses of the 15 variables revealed significantly better performance for nondrug average on 13 variables compared with CBZ, and on four compared with GBP. GBP was better than nondrug average on one variable. CONCLUSIONS: Although both CBZ and GBP produced some effects, GBP produced significantly fewer untoward cognitive effects compared with CBZ at the dosages used in this study.

Acetates↗
PubMed1998

Magnetic stimulation of visual cortex: factors influencing the perception of phosphenes.

Using transcranial magnetic stimulation of occipital cortex, the authors studied the stimulus parameters that generate phosphenes in healthy volunteers. Single pulses or trains of stimuli readily elicited phosphenes in all subjects. The threshold current needed to elicit perception of phosphenes was essentially the same for stimulus trains from 250 msec to 2000 msec in length, but increased dramatically for trains of shorter duration. The effect of stimulus frequency was variable, with each subject having a distinctive "frequency tuning curve," but overall, the threshold current necessary to produce phosphenes decreased as frequency of stimulation increased. Using paired pulses, the perceptual threshold was flat for interstimulus intervals between 2 msec and 100 msec, but increased rapidly as the interstimulus interval was increased above 100 msec. Stimulation of sites lateral to the midline elicited phosphenes in the contralateral visual field. Phosphenes were dominant in the lower and peripheral aspects of the visual fields. The findings are discussed in relation to similar studies of electrical stimulation of somatosensory cortex.

Adult↗
PubMed1998

Physiology of somatosensory perception: cerebral lateralization and extinction.

OBJECTIVE: To demonstrate the effects of cerebral lateralization and temporal dynamics on somatosensory perception. BACKGROUND: We postulated that perceptual thresholds for simple somatosensory stimuli would be less in the left than the right hand, and that a left/right asymmetry in extinction would exist in healthy right-handed subjects (but not in left-handed subjects). During the course of these experiments we also examined the controversy concerning the temporal dynamics of somatosensory perception. METHODS: A total of 126 healthy subjects (age range, 6 to 73 years) participated in the study. Effects of handedness, age, vigilance, gaze, and temporal interval on somatosensory perception were examined in a series of experiments. Brief electric pulses were applied to the index finger of one or both hands. RESULTS: Perceptual thresholds are lower in the left than the right hand of healthy right-handed subjects in a large cohort across a wide age range. Left-handed subjects have no overall asymmetry. Even after compensation for baseline threshold differences, single stimuli in right-handed subjects are perceived more readily in the left than the right hand, and left-hand targets are more difficult to mask. Leftward eye/head gaze lowers thresholds in both hands of right-handed subjects (compared with right or straight gaze). Extinction was consistently maximal when the mask followed the target by 50 to 100 msec. CONCLUSIONS: The findings demonstrate clearly that left/right perceptual thresholds for simple somatosensory stimuli are asymmetric in healthy right-handed subjects. Both central and peripheral asymmetries exist. The central asymmetry and gaze effects are consistent with right cerebral dominance for externally directed attention. Access of somatosensory stimuli to conscious awareness is delayed and particularly vulnerable to disruption at 50 to 100 msec after onset of the stimulus.

Adolescent↗
PubMed1996

Assay of neutralizing antibodies to animal rotavirus strains and human rotavirus serotype G8 by a modified method in the residents of Pune, India.

In the western literature, four G serotypes (G1-G4) of human rotaviruses have been found to be of a major epidemiological importance. During the analysis of rotavirus serotypes from faecal samples in Pune, over 50% of specimens could not be serotyped with the available monoclonal antibodies against G1-G4 serotypes. The results prompted to look for the prevalence of neutralizing antibodies against serotypes other than the major human serotypes (G1-G4) in adults. Neutralizing antibodies against animal rotavirus serotype, viz. G3, G6 and G10, and human rotavirus serotype G8 were determined in adult sera, by a modified technique, which is ELISA-based and mechanized. The results showed that, of the 68 sera tested at 1:100 dilution, 65 (95.58%) were reactive for G3 (SA-11), 52 (76.47%) for G6 (Bovine Lincoln), 6 (8.82%) for G10 (B223), and 40 (58.82%) for G8 (M69) serotypes. It appears that the prevalence of rotaviruses in India may be quite different from that in the developed countries.

Adult↗
PubMed1992

Diazepam effects on the P3 event-related potential.

Cerebral event-related potentials arise from synchronous neural activity associated with cognitive processing. The P3 is a late positive component that is related to task complexity and is directly proportional to stimulus evaluation time. P3 latency and amplitude were examined after oral administration of diazepam, a commonly prescribed medication with known cognitive side effects. Latency of the P3 was significantly increased after a single dose of both 5 and 10 mg of diazepam but not after placebo. P3 amplitude decreased slightly, but not significantly after 10 mg of diazepam. Changes in P3 occurred in the absence of significant changes in the preceding evoked waves (N1, P2). These findings should be considered when the P3 is obtained for clinical or research purposes from medicated patients.

Acoustic Stimulation↗
PubMed1991

Lesions of nucleus basalis alter ChAT activity and EEG in rat frontal neocortex.

The EEG was recorded from frontal, parietal and visual cortices of sham-operated control rats and rats having ibotenic acid lesions of the nucleus basalis. Recordings were made during a period of rest and during stimulus-evoked desynchronization. Spectral power was determined using a Fast Fourier Transform routine; 3 artifact-free 4 sec epochs of resting activity and two 4 sec epochs of activated EEG were analyzed. Choline acetyltransferase activity (ChAT) was measured in each cortical area and was reduced in lesioned animals an average of 25% in frontal cortex, 19% in the parietal region and 10% in visual cortex. The percent of low frequency activity (1-12 Hz) in the frontal EEG was significantly greater in lesioned animals than in the control group during quiet rest; a significant correlation was found between ChAT activity and power in this band. Desynchronized activity was largely unaffected except for a reduction in 25-31 Hz activity in the frontal cortex of lesioned animals. EEG activity in both the parietal and visual areas was unchanged from control values.

Animals↗
PubMedDate not supplied

Effects of scopolamine on visual evoked potentials in aging and dementia.

The unusual combination of a normal pattern reversal VEP and a delayed flash VEP has been reported in patients with dementia of Alzheimer's type (DAT). Hyoscine hydrobromide has been reported to produce a similar VEP abnormality in young, healthy subjects. In the present study, we assessed the relative sensitivity of DAT patients and healthy young, middle-aged and elderly subjects to temporary cholinergic blockade. We report VEP latency values following 3 doses of scopolamine and after a peripheral anticholinergic agent. Flash P2 latency was not significantly slower in DAT patients than in the healthy elderly. Scopolamine increased P2 latency in the young controls but did not affect any other group. The pattern reversal P100 was normal in DAT, and a significant increase in latency occurred following scopolamine administration in both the control and patient groups.

Adult↗