Biomedical subjects

Esther Marx

Publications and source records attributed to Esther Marx.

6 recordsLinked to original sources

PubMed2004

Areas MT/V5 and their transcallosal connectivity in cortical dysplasia by fMRI.

A patient with unilateral focal cortical dysplasia with a significant impairment of visual motion perception within the contralateral hemifield was examined with fMRI. During hemifield visual motion stimulation primary visual cortex areas were activated contralaterally and deactivated ipsilaterally to the stimulated hemifield. Transcallosal visuo-visual interaction was further evident as bilateral activation in temporo-occipital areas that best correspond to the motion sensitive areas MT/V5. MT/V5 was displaced anteriorly, superiorly, and medially within the dysplastic hemisphere and separated into two distinct activation clusters. During visual motion stimulation the parieto-insular vestibular cortex showed signal decreases that agree with the concept of inhibitory visuo-vestibular interaction. Thus, fMRI is a suitable tool for detecting preserved function and transcallosal connections in patients with focal cortical dysplasia.

Adult↗

PubMed2004

Eyes open and eyes closed as rest conditions: impact on brain activation patterns.

The patterns of associated brain activations during eyes-open and eyes-closed states in complete darkness considerably differ in fMRI. An "interoceptive" state with the eyes closed is characterized by visual cortex activation, while an "exteroceptive" state with the eyes open is characterized by ocular motor system activity. The impact of the chosen rest condition (eyes open or eyes closed in complete darkness) on the pattern of brain activations during visual stimulation was evaluated in 14 healthy volunteers. During fixation or dim light room illumination, the activation of the visual cortex was larger with the eyes-open rest condition than with the eyes-closed rest condition; however, activation of the lateral geniculate nucleus was smaller. Activations that can be attributed to ocular motor structures, such as the prefrontal cortex, parietal and frontal eye fields, cerebellar vermis, the thalamus, and basal ganglia were larger with the eyes-closed rest condition than with the eyes-open rest condition. BOLD signal decreases of cortical areas that represent visual, somatosensory, auditory, and vestibular functions were seen in the comparison fixation of light emitting diode (LED) minus eyes closed. Thus, the choice of rest condition (either eyes closed or eyes open) is critical for stimulus-induced brain activation patterns. Activity of the ocular motor system as well as deactivation of sensory cortical areas may go undetected with eyes open as rest condition.

Adolescent↗

PubMed2003

Eye closure in darkness animates sensory systems.

Single subject and group analyses (n = 12) showed that the eyes-open and eyes-closed states in complete darkness considerably and consistently differ in the patterns of associated brain activation in fMRI. During nonchanging external stimulation, ocular motor and attentional systems were activated when the eyes were open; the visual, somatosensory, vestibular, and auditory systems were activated when the eyes were closed. These data suggest that there are two different states of mental activity: with the eyes closed, an "interoceptive" state characterized by imagination and multisensory activity and with the eyes open, an "exteroceptive" state characterized by attention and ocular motor activity. Our study also shows that the chosen baseline condition may have a considerable impact on activation patterns and on the interpretation of brain activation studies.

Adult↗

PubMed2003

Influence of captopril on symptomatic and hormonal responses to hypoglycaemia in humans.

AIMS: Hypoglycaemic symptoms and hormonal counter-regulation are of high importance to avoid the risk of severe hypoglycaemia in patients with diabetes mellitus. Various antihypertensive drugs, such as angiotensin-converting enzyme (ACE) inhibitors, have been suspected for a long time to reduce this response to hypoglycaemia in diabetic subjects. Although ACE inhibitors are approved for controlling diabetic complications, previous investigations regarding this putative side-effect are controversial. METHODS: We performed clamp experiments in 16 healthy men lasting for 6 h each. The subjects were pretreated for 7 days with captopril 3 x 25 mg day-1 vs placebo in a randomized, double-blind, crossover study. Plasma glucose was decreased in a stepwise manner during a hypoglycaemic clamp session and counter-regulatory hormones [epinephrine (adrenaline), norepinephrine (adrenaline), ACTH, cortisol, glucagon], symptoms, and haemodynamic parameters (blood pressure, heart rate] were measured. RESULTS: Counter-regulatory hormone concentrations significantly increased in both sessions (ACE inhibitor vs placebo) during hypoglycaemia. The rise of counter-regulatory hormones as well as symptom scores were equal under both ACE inhibitor and placebo treatment. Systolic blood pressure and heart rate increased (from 110 +/- 3 vs 115 +/- 3 mmHg to 132 +/- 4 vs 133 +/- 4 mmHg) whereas diastolic blood pressure slightly decreased (from 63 +/- 2 vs 70 +/- 3 mmHg to 61 +/- 2 vs 64 +/- 2 mmHg) independent of pretreatment. Systolic and diastolic blood pressure were significantly lower in the captopril session vs placebo (P < 0.05). CONCLUSIONS: Our results demonstrate that subchronic treatment with captopril does not attenuate symptomatic and hormonal response to hypoglycaemia. Thus, to patients at risk of hypoglycaemia who require antihypertensive or nephroprotective treatment, we would continue giving an ACE inhibitor.

Adult↗

PubMed2003

Inhibitory interhemispheric visuovisual interaction in motion perception.

Findings of an earlier functional magnetic resonance imaging (fMRI) study that coherent motion stimulation of the right or left visual hemifield exhibited negative signal changes (deactivations) in the primary visual cortex and the lateral geniculate nucleus contralateral to the stimulated hemisphere were evaluated to determine the functional significance of this contralateral inhibition of the visual system. Fourteen subjects participated in a psychophysical study on the perception of single object motion (0.4 degrees /s) in one visual hemifield with or without concurrent coherent motion stimulation of the contralateral hemifield. Mean detection times for horizontal object motion (0.5 +/- 0.19 vs. 0.61 +/- 0.22 s) and vertical object motion (0.53 +/- 0.19 vs. 0.72 +/- 0.34 s) were significantly prolonged during concurrent motion pattern stimulation in the contralateral hemifield. These data support the interpretation that the deactivation of neuronal activity in the visual system found by fMRI is associated with a functional decrement in the sensitivity needed to perceive motion and may reflect transcallosal attentional shifts between the two hemispheres.

Adult↗

PubMed2002

Lid closure mimics head movement in fMRI.

Motion correction algorithms are commonly used to correct for involuntary head motions in fMRI. We found that lid closure increased signal intensity of the eyes by a factor of 1.6 to 2 in EPI-fMRI. If the eyes were included in the scanning volume, transitions from eyes open to eyes closed in darkness were regularly associated with erroneously detected head translations along the z-axis and head rotations around the x-axis in Talairach's coordinate system. These artefacts could be avoided by masking the eyes in the images during the estimation of movement parameters.

Adult↗