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Right-handed Subjects (right-handed + subject)

Distribution by Scientific Domains

Life Sciences	80%

Selected Abstracts

Functional neuroanatomy of the human near/far response to blur cues: eye-lens accommodation/vergence to point targets varying in depth

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2004
Hans O. Richter
Abstract The purpose of this study was to identify the networks involved in the regulation of visual accommodation/vergence by contrasting the cortical functions subservient to eye-lens accommodation with those evoked by foveal fixation. Neural activity was assessed in normal volunteers by changes in rCBF measured with PET. Thirteen right-handed subjects participated in three monocular tasks: (i) resting with eyes closed; (ii) sustained foveal fixation upon a LED at 1.2 m (0.83 D); and (iii) accommodating alternately on a near (24 cm, 4.16 D) vs. a far (3.0 m, 0.33 D) LED alternately illuminated in sequential 2 s epochs. The contrast between the conditions of near/far accommodation and of constant foveal fixation revealed activation in cerebellar hemispheres and vermis; middle and inferior temporal cortex (BA 20, 21, 37); striate cortex and associative visual areas (BA 17/18). Comparison of the condition of constant fixation with the condition of resting with closed eyes indicated activation of cerebellar hemispheres and vermis; visual cortices (BA 17/18); a right hemisphere dominant network encompassing prefrontal (BA 6, 9, 47), superior parietal (BA 7), and superior temporal (BA 40) cortices; and bilateral thalamus. The contrast between the conditions of near/far accommodation with closed-eye rest reflected an incremental summation of the activations found in the previous comparisons (i.e. activations associated with constant fixation). Neural circuits activated selectively during the near/far response to blur cues over those during constant visual fixation, occupy posterior structures that include occipital visual regions, cerebellar hemispheres and vermis, and temporal cortex. [source]

Effector-independent representations of simple and complex imagined finger movements: a combined fMRI and TMS study

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2003
J. P. Kuhtz-Buschbeck
Abstract Kinesthetic motor imagery and actual execution of movements share a common neural circuitry. Functional magnetic resonance imaging was used in 12 right-handed volunteers to study brain activity during motor imagery and execution of simple and complex unimanual finger movements of the dominant and the nondominant hand. In the simple task, a flexible object was rhythmically compressed between thumb, index and middle finger. The complex task was a sequential finger-to-thumb opposition movement. Premotor, posterior parietal and cerebellar regions were significantly more active during motor imagery of complex movements than during mental rehearsal of the simple task. In 10 of the subjects, we also used transcranial magnetic brain stimulation to examine corticospinal excitability during the same motor imagery tasks. Motor-evoked potentials increased significantly over values obtained in a reference condition (visual imagery) during imagery of the complex, but not of the simple movement. Imagery of finger movements of either hand activated left dorsal and ventral premotor areas and the supplementary motor cortex regardless of task complexity. The effector-independent activation of left premotor areas was particularly evident in the simple motor imagery task and suggests a left hemispherical dominance for kinesthetic movement representations in right-handed subjects. [source]

Group-level variations in motor representation areas of thenar and anterior tibial muscles: Navigated Transcranial Magnetic Stimulation Study

HUMAN BRAIN MAPPING, Issue 8 2010
Eini Niskanen
Abstract Navigated transcranial magnetic stimulation (TMS) can be used to stimulate functional cortical areas at precise anatomical location to induce measurable responses. The stimulation has commonly been focused on anatomically predefined motor areas: TMS of that area elicits a measurable muscle response, the motor evoked potential. In clinical pathologies, however, the well-known homunculus somatotopy theory may not be straightforward, and the representation area of the muscle is not fixed. Traditionally, the anatomical locations of TMS stimulations have not been reported at the group level in standard space. This study describes a methodology for group-level analysis by investigating the normal representation areas of thenar and anterior tibial muscle in the primary motor cortex. The optimal representation area for these muscles was mapped in 59 healthy right-handed subjects using navigated TMS. The coordinates of the optimal stimulation sites were then normalized into standard space to determine the representation areas of these muscles at the group-level in healthy subjects. Furthermore, 95% confidence interval ellipsoids were fitted into the optimal stimulation site clusters to define the variation between subjects in optimal stimulation sites. The variation was found to be highest in the anteroposterior direction along the superior margin of the precentral gyrus. These results provide important normative information for clinical studies assessing changes in the functional cortical areas because of plasticity of the brain. Furthermore, it is proposed that the presented methodology to study TMS locations at the group level on standard space will be a suitable tool for research purposes in population studies. Hum Brain Mapp, 2010. © 2010 Wiley-Liss, Inc. [source]

Decreased basal fMRI functional connectivity in epileptogenic networks and contralateral compensatory mechanisms

HUMAN BRAIN MAPPING, Issue 5 2009
Gaelle Bettus
Abstract A better understanding of interstructure relationship sustaining drug-resistant epileptogenic networks is crucial for surgical perspective and to better understand the consequences of epileptic processes on cognitive functions. We used resting-state fMRI to study basal functional connectivity within temporal lobes in medial temporal lobe epilepsy (MTLE) during interictal period. Two hundred consecutive single-shot GE-EPI acquisitions were acquired in 37 right-handed subjects (26 controls, eight patients presenting with left and three patients with right MTLE). For each hemisphere, normalized correlation coefficients were computed between pairs of time-course signals extracted from five regions involved in MTLE epileptogenic networks (Brodmann area 38, amygdala, entorhinal cortex (EC), anterior hippocampus (AntHip), and posterior hippocampus (PostHip)). In controls, an asymmetry was present with a global higher connectivity in the left temporal lobe. Relative to controls, the left MTLE group showed disruption of the left EC-AntHip link, and a trend of decreased connectivity of the left AntHip-PostHip link. In contrast, a trend of increased connectivity of the right AntHip-PostHip link was observed and was positively correlated to memory performance. At the individual level, seven out of the eight left MTLE patients showed decreased or disrupted functional connectivity. In this group, four patients with left TLE showed increased basal functional connectivity restricted to the right temporal lobe spared by seizures onset. A reverse pattern was observed at the individual level for patients with right TLE. This is the first demonstration of decreased basal functional connectivity within epileptogenic networks with concomitant contralateral increased connectivity possibly reflecting compensatory mechanisms. Hum Brain Mapp 2009. © 2008 Wiley-Liss, Inc. [source]

Dizziness is associated with decreased vasoreactivity in right cerebral hemisphere for head-down manoeuvre , near-infrared spectroscopy study

CLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 1 2005
Nobusada Shinoura
Summary To investigate the vasoreactivity of cerebral hemisphere in patients with dizziness and syncope, we compared changes in total haemoglobin (THbl) and regional oxygen saturation (rSO2) of the right and left frontal lobes in response to head-down manoeuvre. Ninety-six right-handed subjects (aged 59 ± 19 years) were asked to perform a head-down or a standing manoeuvre. Head-down manoeuvre produced a greater increase in right side THbl in subjects under 70 years of age (8·5 ± 3·1) when compared with subjects older than 70 years (0·40 ± 0·08). In contrast, the head-down manoeuvre had no effects on left side THbl, irrespective of patient age. Similarly, the head-down manoeuvre resulted in a greater decrease of right side rSO2 in subjects under 70 years of age (,5·2 ± 2·1%) when compared with subjects older than 70 years (0·31 ± 0·9%). In contrast, the head-down manoeuvre had no effects on left side rSO2, irrespective of patient age. The head-down manoeuvre produced a smaller increase in right side THbl in subjects with dizziness (0·38 ± 0·19) than in those without dizziness (9·4 ± 3·5). A standing manoeuvre produced a smaller increase in right side THbl in subjects with syncope (,0·057 ± 0·047) than in those without syncope (0·063 ± 0·028). The head-down manoeuvre produced a decrease in right side rSO2 in subjects without dizziness (,6·4 ± 2·4%) and a slight increase in right side rSO2 in subjects with dizziness (1·1 ± 0·4%). Subjects with dizziness (67 ± 2·1 years) were significantly older than those without dizziness (53 ± 2·7 years) or those with syncope (44 ± 4·2 years). These data indicate that reduced vasoreactivity to right hemispheric pressure changes is associated with dizziness in older subjects. Further, decreases in right hemispheric THbl during a standing manoeuvre are associated with syncope in relatively younger subjects. [source]