Biomedical subjects

Carolyn A Gunraj

Publications and source records attributed to Carolyn A Gunraj.

5 recordsLinked to original sources

PubMed2006

Cortical and spinal abnormalities in psychogenic dystonia.

OBJECTIVE: The pathophysiology of psychogenic dystonia has not been examined, but a growing body of literature suggests that abnormal sensory input from repetitive movements can lead to plastic cortical changes. Reduced cortical and spinal inhibition is well documented in organic dystonia. We tested the hypothesis that aberrant sensory input associated with abnormal posture may cause similar abnormalities by testing patients with psychogenic dystonia. METHODS: We assessed cortical and spinal inhibitory circuits and cortical activity associated with voluntary movement in 10 patients with clinically definite psychogenic dystonia, 8 patients with organic dystonia, and 12 age-matched healthy control subjects. RESULTS: Three measures of cortical inhibition, resting short- and long-interval intracortical inhibition and cortical silent period, were reduced in both psychogenic dystonia and organic dystonia. Cutaneous silent period mediated by spinal circuitries was increased in psychogenic and organic dystonia. Forearm spinal reciprocal inhibition was reduced in psychogenic dystonia. INTERPRETATION: Psychogenic and organic dystonia share similar physiological abnormalities. Previous findings of abnormal cortical and spinal excitability in organic dystonia may, in part, be a consequence rather than a cause of dystonia. Alternatively, these findings may represent endophenotypic abnormalities that predispose to both types of dystonia.

Adult↗

PubMed2005

Representation of facial muscles in human motor cortex.

Whether there is a projection from the primary motor cortex (M1) to upper facial muscles and how the facial M1 area is modulated by intracortical inhibitory and facilitatory circuits remains controversial. To assess these issues, we applied transcranial magnetic stimulation (TMS) to the M1 and recorded from resting and active contralateral (C-OOc) and ipsilateral orbicularis oculi (I-OOc), and contralateral (C-Tr) and ipsilateral triangularis (I-Tr) muscles in 12 volunteers. In five subjects, the effects of stimulating at different scalp positions were assessed. Paired TMS at interstimulus intervals (ISIs) of 2 ms were used to elicit short interval intracortical inhibition (SICI) and ISI of 10 ms for intracortical facilitation (ICF). Long interval intracortical inhibition (LICI) was evaluated at ISIs between 50 and 200 ms, both at rest and during muscle activation. The silent period (SP) was also determined. C-OOc and I-OOc responses were recorded in all subjects. The optimal position for eliciting C-OOc responses was lateral to the hand representation in all subjects and MEP amplitude markedly diminished when the coil was placed 2 cm away from the optimal position. For the I-OOc, responses were present in more scalp sites and the latency decreased with more anterior placement of the coil. C-Tr response was recorded in 10 out of 12 subjects and the I-Tr muscle showed either no response or low amplitude response, probably due to volume conduction. SICI and ICF were present in the C-OOc and C-Tr, but not in the I-OOc muscle. Muscle activation attenuated SICI and ICF. LICI at rest showed facilitation at 50 ms ISI in all muscles, but there was no significant inhibition at other ISIs. There was no significant inhibition or facilitation with the LICI protocol during muscle contraction. The SP was present in the C-OOc, C-Tr and I-OOc muscles and the mean durations ranged from 92 to 104 ms. These findings suggest that the I-OOc muscle response is probably related to the first component (R1) of the blink reflex. There is M1 projection to the contralateral upper and lower facial muscles in humans and the facial M1 area is susceptible to cortical inhibition and facilitation, similar to limb muscles.

Acoustic Stimulation↗

PubMed2005

Effect of low-frequency repetitive transcranial magnetic stimulation on interhemispheric inhibition.

We studied the effects of 1-Hz repetitive transcranial magnetic stimulation (rTMS) on the excitability of interhemispheric connections in 13 right-handed healthy volunteers. TMS was performed using figure-eight coils, and surface electromyography (EMG) was recorded from both first dorsal interosseous (FDI) muscles. A paired-pulse method with a conditioning stimulus (CS) to the motor cortex (M1) followed by a test stimulus to the opposite M1 was used to study the interhemispheric inhibition (ppIHI). Both CS and TS were adjusted to produce motor-evoked potentials of approximately 1 mV in the contralateral FDI muscles. After baseline measurement of right-to-left IHI (pre-RIHI) and left-to-right IHI (pre-LIHI), rTMS was applied over left M1 at 1 Hz with 900 stimuli at 115% of resting motor threshold. After rTMS, ppIHI was studied using both the pre-rTMS CS (post-RIHI and post-LIHI) and an adjusted post-rTMS CS set to produce 1-mV motor evoked potentials (MEPs; post-RIHI(adj) and post-LIHI(adj)). The TS was set to produce 1-mV MEPs. There was a significant reduction in post-LIHI (P = 0.0049) and post-LIHI(adj) (P = 0.0169) compared with pre-LIHI at both interstimulus intervals of 10 and 40 ms. Post-RIHI was significantly reduced compared with pre-RIHI (P = 0.0015) but pre-RIHI and post-RIHI(adj) were not significantly different. We conclude that 1-Hz rTMS reduces IHI in both directions but is predominantly from the stimulated to the unstimulated hemisphere. Low-frequency rTMS may be used to modulate the excitability of IHI circuits. Treatment protocols using low-frequency rTMS to reduce cortical excitability in neurological and psychiatric conditions need to take into account their effects on IHI.

Adult↗

PubMed2003

Short and long latency afferent inhibition in Parkinson's disease.

Sensory abnormalities have been reported in Parkinson's disease and may contribute to the motor deficits. Peripheral sensory stimulation inhibits the motor cortex, and the effects depend on the interstimulus interval (ISI) between the sensory stimulus and transcranial magnetic stimulation (TMS) to the motor cortex. Short latency afferent inhibition (SAI) occurs at an ISI of approximately 20 ms, and long latency afferent inhibition (LAI) at an ISI of approximately 200 ms. We studied SAI and LAI in 10 Parkinson's disease patients with the aim of assessing whether sensorimotor processing is altered in Parkinson's disease. Patients were studied on and off medication, and the findings were compared with 10 age-matched controls. Median nerve and middle finger stimulation were delivered 20-600 ms before TMS to the contralateral motor cortex. The motor evoked potentials were recorded from the relaxed first dorsal interosseous (FDI) muscle. SAI was normal in Parkinson's disease patients off dopaminergic medications, but it was reduced on the more affected side in Parkinson's disease patients on medication. LAI was reduced in Parkinson's disease patients compared with controls independent of their medication status. LAI reduced long interval intracortical inhibition in normal subjects but not in Parkinson's disease patients. The different results for SAI and LAI indicate that it is likely that separate mechanisms mediate these two forms of afferent inhibition. SAI probably represents the direct interaction of a sensory signal with the motor cortex. This pathway is unaffected by Parkinson's disease but is altered by dopaminergic medication in Parkinson's disease patients and may contribute to the side effects of dopaminergic drugs. LAI probably involves other pathways such as the basal ganglia or cortical association areas. This defective sensorimotor integration may be a non-dopaminergic manifestation of Parkinson's disease.

Adult↗

PubMed2002

Synonymous nucleotide substitutions in the neonatal Fc receptor.

The neonatal Fc receptor (FcRn) is a key receptor involved in the transcytosis of IgG across the maternal-fetal barrier. The level of IgG varies considerably among newborn infants. Since other Fc gamma receptors show single nucleotide functional variants, we determined whether common variant alleles exist for the FcRn. Direct sequence analysis was performed on PCR-amplified complementary DNA (cDNA) isolated from ten placental mRNAs (20 alleles examined). Two synonymous nucleotide polymorphisms were detected from the same source. A G251T and C707T substitution, reflecting amino acid positions Pro19 and Arg171 of the mature polypeptide, did not alter the amino acid encoded. No other nucleotide substitutions or sequence variations were observed. Thus, the variation in IgG transport is not due to common variant alleles among the human population. Due to the limited number of samples tested (n=20), low-frequency alleles would go undetected by chance alone when q has a frequency < or = 0.14. It is unlikely that low-frequency variant alleles, if present, are responsible for the major variation seen in the transcytosis of IgG.

Histocompatibility Antigens Class I↗