Search results for "Nial"
showing 10 items of 1680 documents
Modulation of corticospinal excitability by repetitive transcranial magnetic stimulation
2000
Abstract Objective : Repetitive transcranial magnetic stimulation (rTMS) is able to modulate the corticospinal excitability and the effects appear to last beyond the duration of the rTMS itself. Different studies, employing different rTMS parameters, report different modulation of corticospinal excitability ranging from inhibition to facilitation. Intraindividual variability of these effects and their reproducibility are unclear. Methods : We examined the modulatory effects of rTMS to the motor cortex at various frequencies (1, 10, 20 Hz) and at different time-points in twenty healthy volunteers. Results : We observed significant inhibition of MEPs following 1 Hz rTMS and significant facili…
Facilitatory effects of 1 Hz rTMS in motor cortex of patients affected by migraine with aura
2004
We previously showed paradoxical facilitatory effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) on striate and extrastriate cortex of patients suffering migraine with aura. In this study we evaluated the effects of 1 Hz rTMS on the excitability of inhibitory and facilitatory circuits of motor cortex to explore whether the abnormal pattern of excitability extends beyond the sensory cortex also involving motor areas in migraine with aura. Nine patients affected by migraine with aura and eight healthy controls entered into the study. The hot spot for activation of the right abductor pollicis brevis (APB) was checked by means of a figure-of-eight coil and motor thresh…
Repetitive transcranial magnetic stimulation over the left parietal cortex facilitates visual search for a letter among its mirror images
2015
Interference by task irrelevant information is seen in visual search paradigms using letters. Thus, it is harder to find the letter 'N' among its mirror reversals 'Icyrillic' than vice versa. This observation, termed the reversed letter effect, involves both a linguistic association and an interference of task irrelevant information - the shape of 'N' or 'Icyrillic' is irrelevant, the search requires merely distinguishing the tilts of oblique bars. We adapted the repetitive transcranial magnetic stimulation (rTMS) methods that we previously used, and conducted three rTMS experiments using healthy subjects. The first experiment investigated the effects of rTMS on the left and right posterior…
Impairments in top down attentional processes in right parietal patients: Paradoxical functional facilitation in visual search
2014
AbstractIt is well known that the right posterior parietal cortex (PPC) is involved in attentional processes, including binding features. It remains unclear whether PPC is implicated in top-down and/or bottom-up components of attention. We aim to clarify this by comparing performance of seven PPC patients and healthy controls (HC) in a visual search task involving a conflict between top-down and bottom-up processes. This task requires essentially a bottom-up feature search. However, top-down attention triggers feature binding for object recognition, designed to be irrelevant but interfering to the task. This results in top-down interference, prolonging the search reaction time. This interfe…
Serial Measurement of Static and Dynamic Cerebrovascular Autoregulation After Brain Injury
2011
In patients with neuronal injury, the knowledge of the status of cerebrovascular autoregulation can help to optimize the management of the cerebral perfusion pressure. This study characterizes dynamic and static cerebrovascular autoregulation during the first 7 days after severe traumatic brain injury or intracranial hemorrhage.After approval from the IRB, 16 patients were studied. Cerebral blood flow velocity (CBFV) was measured daily for the assessment of dynamic (10 patients) and static (16 patients) cerebrovascular autoregulation in both the middle cerebral arteries using the transcranial Doppler sonography. Dynamic cerebrovascular autoregulation (dAR) was measured using the cuff-deflat…
Transcranial Doppler diagnosis of cerebral vasospasm following subarachnoid haemorrhage: correlation and analysis of results in relation to the age o…
1994
A retrospective analysis was undertaken to determine whether cerebral vasospasm following subarachnoid haemorrhage (SAH) correlates with the age of patients. For at least 3 weeks after bleeding 80 subjects underwent very close follow-up with clinical examination and transcranial Doppler records of the blood velocities within the basal cerebral arteries. Firstly a correlation between measured maximal mean blood flow velocities and age was made. Secondly, according to their age and the maximum of recorded mean velocities (v), the patients were divided into groups as follows: age 55 years or less, age more than 55 years; and maximum velocity v190 cm/s, 90 cm/sv2120 cm/s, 120 cm/sv3160 cm/s, v4…
Exploring metrics for the characterization of the cerebral autoregulation during head-up tilt and propofol general anesthesia
2022
Techniques grounded on the simultaneous utilization of Tiecks' second order differential equations and spontaneous variability of mean arterial pressure (MAP) and mean cerebral blood flow velocity (MCBFV), recorded from middle cerebral arteries through a transcranial Doppler device, provide a characterization of cerebral autoregulation (CA) via the autoregulation index (ARI). These methods exploit two metrics for comparing the measured MCBFV series with the version predicted by Tiecks' model: normalized mean square prediction error (NMSPE) and normalized correlation rho. The aim of this study is to assess the two metrics for ARI computation in 13 healthy subjects (age: 27 & PLUSMN; 8 yr…
Control for carbon dioxide-related changes in flow velocity by transcranial Doppler monitoring.
1994
Transcranial Doppler ultrasonography can monitor changes in intracranial blood flow velocity over time in a variety of experimental and clinical settings with excellent temporal resolution. Alterations in arterial carbon dioxide pressure exert a profound influence on blood flow velocity. Such changes exhibit important individual fluctuation depending on respiratory status. This limits the ability of transcranial Doppler to accurately study subtle changes in blood flow velocity, independent of the respiratory state of the subject. Suggested here is a method to control for the respiration artifact on blood flow velocity. The middle cerebral artery of 7 healthy male volunteers was studied with…
Modulation of premotor mirror neuron activity during observation of unpredictable grasping movements.
2004
Using transcranial magnetic stimulation, we explored the properties of premotor mirror neurons during the passive observation of a reaching-grasping movement in human subjects. Two different experiments were run using video-clips as visual stimuli. Video-clips showed a normally performed (control stimulus) or an anomalous reaching-grasping movement executed by delaying the time of the appearance of the maximal finger aperture (experiment 1), or substituting it with an unpredictable closure (experiment 2). Motor evoked potentials were recorded at different time-points during the observation of the video-clips. Profiles of cortical excitability were drawn and compared with the kinematic profi…
Release of premotor activity after repetitive transcranial magnetic stimulation of prefrontal cortex
2008
In the present study we aimed to explore by means of repetitive transcranial magnetic stimulation (rTMS) the reciprocal influences between prefrontal cortex (PFC) and premotor cortex (PMC). Subjects were asked to observe on a computer monitor different pictures representing manipulations of different kind of tools. They had to produce a movement (go condition) or to keep the resting position (no-go condition) at the appearance of different cue signals represented by different colors shown alternatively on the hands manipulating the tools or on the picture background. Motor evoked potentials (MEPs) were collected at the offset of the visual stimuli before and after a 10 minute, 1 Hz rTMS tra…