Search PubMed⌕ Search

Biomedical subjects

B Conrad

Publications and source records attributed to B Conrad.

At least 55 records · Page 3Linked to original sources
PubMed2000

Subthreshold 5-Hz repetitive transcranial magnetic stimulation of the human primary motor cortex reduces intracortical paired-pulse inhibition.

Paired-pulse transcranial magnetic stimulation (TMS) at short interstimulus intervals was employed to investigate short-term effects of 5-Hz repetitive TMS (rTMS) over the primary motor hand area (M1(HAND)) on intracortical excitability. In ten healthy individuals, 1250 pulses of 5-Hz rTMS were applied at 90% of motor resting threshold over the left M1(HAND). Ten minutes after 5-Hz rTMS, paired-pulse inhibition was significantly reduced, whereas paired-pulse facilitation was not modified. Sham-rTMS had no lasting effect on intracortical excitability. These findings suggest that subthreshold 5-Hz rTMS causes a short-term modulation of the excitability of intracortical circuitry in the stimulated M1(HAND). The lasting effect of subthreshold 5-Hz rTMS on intracortical inhibition provides a useful probe for studying short-term plasticity of the human M1(HAND).

Adult↗
PubMed2000

Disturbance of venous flow patterns in patients with transient global amnesia.

Transient global amnesia (TGA) is an inability to form new memories. The pathophysiology and cause of TGA have not been defined. We examined the changes of internal jugular venous flow patterns in 21 patients with TGA and 21 age-matched and sex-matched controls using duplex ultrasonography during two Valsalva manoeuvres (blocking venous return through the superior vena cava). During both manoeuvres a retrograde flow component was seen significantly more frequently in the TGA group than in the controls. Ten patients reported Valsalva-like activities preceding TGA. In these patients a retrograde flow component took place more frequently than in those who did not report preceding Valsalva-like activities. Our results lend support to the hypothesis that TGA may be attributable to venous congestion, and consequent venous ischaemia to bilateral diencephalic or hippocampal structures.

Aged↗
PubMed2000

Relationship between circadian blood pressure patterns and progression of early carotid atherosclerosis: A 3-year follow-up study.

BACKGROUND: Arterial hypertension is a major risk factor for cardiovascular damage. The results of several studies suggest that target organ damage is greater in hypertensive persons with high blood pressure variability. METHODS AND RESULTS: During 3.3 years of follow-up, we studied the relationship between circadian blood pressure changes and the progression of early carotid atherosclerosis in 286 patients aged >55 years. Blood pressure patterns were evaluated with a long-term blood pressure monitor, and the extent of atherosclerosis was measured as the intima-media wall thickness (IMT) of the common carotid artery. Patients were subdivided according to blood pressure variability. The progression of IMT was significantly greater in the patients with increased systolic blood pressure variability (0.11 mm/y [95% CI 0.09 to 0.14] versus 0.05 mm/y [0.03 to 0.08]; P:<0.005) even after adjustment for other risk factors. Multivariate regression analysis revealed the daytime systolic blood pressure variability to be the best predictor for the progression of IMT. Raised daytime systolic blood pressure variability (>15 mm Hg) is associated with an increased relative risk of the development of early atherosclerosis (3.9 [1.4 to 11.1]; P:<0.01) and of cardiovascular events (1.87 [1.08 to 3.20]; P:<0.01). CONCLUSIONS: The daytime systolic blood pressure variability is a strong predictor of early carotid atherosclerosis progression and is useful to define the risk-benefit ratio of therapeutic approaches.

Aged↗
PubMed2000

Short-term motor improvement after sub-threshold 5-Hz repetitive transcranial magnetic stimulation of the primary motor hand area in Parkinson's disease.

Ten unmedicated patients with Parkinson's disease received sub-threshold 5-Hz repetitive transcranial magnetic stimulation (rTMS) over the primary motor hand area (M1(HAND)) contralaterally to the more affected upper limb. Compared to a midfrontal sham-rTMS, real-rTMS over M1(HAND) was associated with a significant decrease in the global motor UPDRS score 1 h after the cessation of rTMS. This was mainly due to a clinical improvement in the arm contralaterally to the stimulated M1(HAND). These preliminary data suggest that focal rTMS of M1(HAND) may have a therapeutic potential in PD.

Electromagnetic Fields↗
PubMed2000

Repetitive transcranial magnetic stimulation causes a short-term increase in the duration of the cortical silent period in patients with Parkinson's disease.

In ten patients with Parkinson's disease (PD) and ten age-matched healthy controls, we applied 15 30-s trains of subthreshold 5-Hz repetitive transcranial magnetic stimulation (rTMS) over the primary motor hand area. Ten minutes after rTMS, PD patients showed a significant prolongation of the transcranially evoked silent period (SP) in the contralateral first dorsal interosseus muscle, whereas the SP remained unchanged in healthy subjects. Since the duration of the transcranially evoked SP is a well-established measure of intracortical inhibition, this finding demonstrates that rTMS is capable of inducing a short-term increase in intracortical inhibition in PD. The lack of a prolongation of the SP in healthy controls suggests that PD patients may be particularly susceptible to modulatory effects of rTMS on motocortical inhibition.

Adult↗
PubMed2000

Lasting cortical activation after repetitive TMS of the motor cortex: a glucose metabolic study.

OBJECTIVE: Cerebral [18F]fluorodeoxy-D-glucose PET ([18F]FDG-PET) was used to visualize the lasting neuronal activation after repetitive transcranial magnetic stimulation (rTMS) over the left hand area of the primary motor cortex (M1HAND). BACKGROUND: Applied over M1HAND, rTMS has been shown to produce a modulation of corticomotor excitability beyond the time of stimulation itself. METHODS: Eight right-handed subjects underwent nonquantitative [18F]FDG-PET measurements during two experimental conditions: at rest and after focal subthreshold 5-Hz rTMS over the left M1HAND. In the post-rTMS condition, [18F]FDG was injected immediately after the administration of 1,800 magnetic pulses over the left M1HAND. Relative differences in normalized regional cerebral metabolic rate of glucose (normalized rCMRglc) between conditions were determined using a voxel-by-voxel Student's t-test and volume-of-interest (VOI) analysis. Analysis was a priori restricted to the M1HAND, the supplementary motor area (SMA), and the primary auditory cortex of both hemispheres. RESULTS: A 5-Hz rTMS of the left M1HAND caused a lasting relative increase in normalized rCMRglc within the M1HAND bilaterally and the SMA. The magnitude and the topographic pattern of persisting relative rCMRglc increases within these motor cortical areas demonstrated considerable interindividual variations. CONCLUSIONS: Subthreshold 5-Hz repetitive transcranial magnetic stimulation (rTMS) over the hand area of the primary motor cortex is associated with a persisting neuronal activation in a distinct set of motor cortical areas beyond the time of stimulation. The current findings demonstrate that [18F]FDG-PET can localize and quantify regional net changes in synaptic cortical activity after rTMS and thus might elucidate the mechanisms underlying rTMS-associated therapeutic effects.

Adult↗
PubMed2000

Extent of cerebral white matter lesions is related to changes of circadian blood pressure rhythmicity.

OBJECTIVE: To evaluate the relationship between circadian blood pressure patterns and the extent of cerebral white matter lesions (WML). DESIGN: Case-control study. PARTICIPANTS: A total of 227 healthy subjects older than 55 years were investigated. Extent and occurrence of WML were evaluated using a computer-supported image analysis system. Circadian blood pressure variation was defined as the average percentage change of nighttime blood pressure compared with the daily blood pressure values. RESULTS: Subjects with WML were significantly older and showed more often a history of hypertension, elevated average systolic daily blood pressure, a reduced systolic circadian blood pressure variation, and an increased incidence of pathological nighttime blood pressure increases. A significant correlation was found between systolic circadian blood pressure variation and the extent of WML. A multiple regression analysis revealed that this parameter was best correlated with the extent of WML. CONCLUSION: In addition to the absolute level of blood pressure, systolic circadian blood pressure variation and in particular a systolic nighttime blood pressure increase may play an important role in the pathogenesis of WML.

Aged↗
PubMed2000

Correlation between quantitative EMG and muscle MRI in patients with axonal neuropathy.

The aim of the study was to investigate whether there are correlations between electromyography (EMG) data and findings in muscle magnetic resonance imaging (MRI). Quantitative EMG data and the amount of pathologic spontaneous activity (PSA) were compared with MRI signal intensities of the tibialis anterior muscles of 20 patients with axonal polyneuropathy and 14 healthy subjects. Using hierarchical regression analysis, the mean motor unit action potential (MUAP) size index (SI) and the amount of PSA were accurate predictors of T1-weighted signal intensity in MRI, an expression of fatty degeneration. The MUAP SI was superior to MUAP amplitude in explaining the variance of T1 signal intensity. Age was not a relevant factor. A high correlation was found between the amount of PSA and the T2-weighted signal intensity in short tau inversion recovery sequence. Magnetic resonance imaging demonstrates the structural changes and thus visualizes the outcome of the functional changes of denervation and reinnervation detected by EMG.

Action Potentials↗
PubMed1999

Expression of metabotropic glutamate receptor subtype mRNA (mGluR1-8) in human cerebellum.

The expression of metabotropic glutamate receptor (mGluR) mRNAs in the human cerebellar neocortex was investigated using in situ hybridization. mGluR1, 3 and 4 mRNAs were most abundant and widely distributed, whereas mGluR2, 5 and 7 mRNA expression was circumscript. mRNAs coding for mGluR1, 3, 4 and 7 were expressed in Purkinje cells. mGluR1 and 4 mRNAs detectable in granule cells and mGluR1, 2, 3, 4 and 7 mRNAs in Golgi cells. mGluR5 mRNA was detectable in putative Bergmann glia as well as mGluR3 mRNA, which was widely expressed in glial cells. mGluR8 mRNA expression was very low in a subset of stellate/basket cells of the molecular layer whereas mGluR6 mRNA was not detectable in the cerebellar cortex.

Aged↗
PubMed1999

Imaging functional activation of the auditory cortex during focal repetitive transcranial magnetic stimulation of the primary motor cortex in normal subjects.

Positron emission tomography (PET) during focal repetitive transcranial magnetic stimulation (rTMS) has emerged as a promising approach to study cortical connectivity in awake humans. However, the noise caused by the discharging magnetic coil might have confounding effects on the rTMS-related cortical activation pattern. In twelve healthy volunteers, 18-fluoro-2-deoxy-D-glucose (18FDG) PET was employed to visualize the functional activation of the primary auditory cortex (PAC) during 2 Hz rTMS of the left primary sensorimotor hand area. Magnetic stimuli (1800) were applied at an intensity of 140% of motor resting threshold during the uptake period of 18FDG. Though all subjects wore earplugs, rTMS-related noise induced a consistent bilateral increase of regional glucose utilization in the PAC (P < 0.05, corrected). Thus, rTMS-related acoustic input needs to be taken into account in combined rTMS/PET studies.

Adult↗
PubMed1999

Reversal of thermal hyperalgesia in a rat partial sciatic nerve ligation model by Prosaptide TX14(A).

We used the partial sciatic nerve ligation (PSL) model of Seltzer to assess thermal hyperalgesia after administration of Prosaptide 14-mer, TX14(A). At a dose of 200 microg/kg in Wistar rats, subcutaneous delivery of TX14(A) reversed thermal hyperalgesia at 3 and 24 h. Values declined at 48 h and returned to baseline at 72 h. A dosing study of TX(14)A gave a dependent response with 100 microg/kg having a similar potency to the 200 microg/kg study with 50 and 10 microg/kg responding somewhat lower. When TX(14)A was administered every fourth day for 12 days at 100 microg/kg, 24 h post injection values returned to baseline each time. Our results suggest that Prosaptide may have potential for therapeutic use in neuropathic pain syndromes in humans.

Amino Acid Sequence↗
PubMed1999

Abnormal increase in the corticomotor output to the affected hand during repetitive transcranial magnetic stimulation of the primary motor cortex in patients with writer's cramp.

In fourteen right-handed patients with writer's cramp and 10 right-handed controls, 10 trains of suprathreshold 1 Hz repetitive transcranial magnetic stimulation (rTMS) were applied over the left primary motor hand area. Each rTMS train lasted for a minute with an intertrain interval of 10 s. The motor evoked potentials (MEPs) were recorded from the relaxed contralateral first dorsal interosseus muscle. The mean MEP area of each rTMS train was taken as a measure of the corticospinal motor output to the affected hand. While the mean MEP area decreased significantly in controls, patients showed a significant increase in mean MEP area during rTMS. The differential effect on MEP size was highly significant. The abnormal rTMS-associated facilitation of the corticomotor output to the affected hand demonstrates an increased excitability of the corticospinal motor system in writer's cramp.

Adult↗
PubMed1999

Repetitive transcranial magnetic stimulation has a beneficial effect on bradykinesia in Parkinson's disease.

The effect of focal 5 Hz repetitive transcranial magnetic stimulation (rTMS) of the motor hand area (M1) on bradykinesia was studied in 12 unmedicated patients with Parkinson's disease (PD). On 2 separate days, a real-rTMS was applied to M1 contralaterally to the more severely affected limb or a frontal sham-rTMS was applied 3 cm anteriorly to Fz in a random order. Stimulus intensity was 10% below resting motor threshold. Before and 20 min after rTMS, patients performed 15 consecutive pointing movements with the index finger contralaterally to the stimulated M1. Compared with sham-rTMS, real-rTMS over the contralateral M1 caused a significant decrease in total movement time without affecting end-point accuracy. Our data provide evidence that 5 Hz rTMS over M1 can improve bradykinesia in PD patients beyond the time of magnetic stimulation.

Adult↗
PubMed1999

A positron emission tomographic study of subthalamic nucleus stimulation in Parkinson disease: enhanced movement-related activity of motor-association cortex and decreased motor cortex resting activity.

BACKGROUND: Long-term high-frequency stimulation of the subthalamic nucleus (STN) improves akinesia in Parkinson disease. The neural correlates of STN stimulation are not well understood. Positron emission tomography can be applied to the in vivo study of the mechanisms of deep brain stimulation. OBJECTIVE: To study changes in regional cerebral blood flow as an index of synaptic activity in patients with Parkinson disease with effective STN stimulation on and off during rest and movement. METHODS: Eight patients with Parkinson disease who had electrodes implanted in the STN underwent 12 measurements of regional cerebral blood flow with water O 15 positron emission tomography at rest and during performance of paced freely selected joystick movements, both with and without STN stimulation (3 scans per experimental condition). Motor performance and reaction and movement times were monitored. Statistical parametric mapping was used to compare changes in regional cerebral blood flow between conditions and differences in activation. RESULTS: All patients showed improvement in reaction and movement times during scans with the stimulator on. As predicted, increases in activation of rostral supplementary motor area and premotor cortex ipsilateral to stimulation were observed when stimulation was on during contralateral movement (P<.001). Unpredicted observations included decreases in regional cerebral blood flow in primary motor cortex at rest induced by STN stimulation. CONCLUSION: Stimulation of the STN reduces the movement-related impairment of frontal motor association areas and the inappropriate motor cortex resting activity in Parkinson disease.

Adult↗