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Biomedical subjects

M Burghoff

Publications and source records attributed to M Burghoff.

28 records · Page 2Linked to original sources
PubMed1997

Somatotopic source arrangement of 600 Hz oscillatory magnetic fields at the human primary somatosensory hand cortex.

Based on low-noise superconducting quantum interference devices (SQUIDs) magnetoencephalography allows the non-invasive detection of low-amplitude high-frequency brain responses evoked about 20 ms after electric hand nerve stimulation. The main spectral energy of these brief oscillatory bursts (near 600 Hz) is in the range typical for rapidly repeated action potentials. Here, the magnetic fields of median and ulnar nerve evoked 600 Hz bursts are shown to exhibit a somatotopic arrangement at the primary somatosensory hand cortex closely resembling that of the concomitant postsynaptic primary cortical response (¿N20m'). Two possible burst generators are discussed: (1) repetitive spike volleys conducted along the terminal segments of somatotopically arranged thalamocortical axons, and (2) early intracortical spike activity in nerve-specific subterritories of the 3b hand area.

Brain Mapping↗
PubMed1997

Visuo-motor adaptation: evidence for a distributed amplitude control system.

We investigated the constraints for visuo-motor adaptation in human pointing movements. Subjects pointed at sequentially presented visual targets while visual feedback about their finger position was either absent (pre- and post-period), or was manipulated such as to require a gradual reduction of response amplitude (per-period). We found that response amplitudes were smaller during the post- than during the pre-period, which documents the existence of adaptation to distorted visual feedback. We further found that adaptation can transfer fully to untrained amplitudes (Exp. 1), although the amount of transfer may be reduced if trained and untrained amplitudes are substantially different (Exp. 2). However, selective adaptation of one amplitude but not another can also be yielded if the paradigm explicitly asks for it (Exp. 3), and if the two amplitudes differ by more than about 10 cm (Exp. 4). We conclude from these findings that the adapted mechanism consists of amplitude-specific elements, tuned to amplitude spans of some 10 cm.

Adaptation, Physiological↗
PubMed1997

Mapping of tibial nerve evoked magnetic fields over the lower spine.

Using a low-noise 49-channel dc-SQUID system spinal somatosensory evoked fields (SEF) were recorded which were generated by compound action currents evoked upon posterior tibial nerve stimulation. The SEF mapping showed the action current propagation along the sciatic nerve, lumbosacral plexus and cauda equina in parallel to simultaneously recorded electrical potentials (SEP). For a reliable intraindividual side-to-side comparison of spinal SEFs the right and left tibial nerves were stimulated in alternating order; this procedure minimizes artifactual inter-nerve SEF map differences due to eventual patient-to-sensor displacements which might occur in serial measurements. These large-area lumbar SEF mappings open up several clinical perspectives for magnetoneurography, in particular with respect to the 3D-localization of proximal conduction blocks.

Adult↗
PubMed1997

Magnetocardiography and 32-lead potential mapping: repolarization in normal subjects during pharmacologically induced stress.

Signals from 37 magnetocardiographic sensors and simultaneously recorded 32 ECG leads were obtained in three healthy male subjects (including two reinvestigations). After recordings at rest, the heart rate was increased by pharmacologic stress (117 to 142 beats/min). Comparison of the repolarization of rest and stress showed substantial changes in the magnetocardiogram (MCG) up to T wave inversions during stress. In the ECG only junctional ST-T segment shifts were present. For quantification, correlation coefficients between pairs of rest and stress MCG and rest and stress ECG distributions were calculated for the same time instant at the beginning of T wave under rest and stress conditions. In addition, equivalent electrical current dipole moment and magnetic dipole moment vectors were calculated from the MCG, and their change from rest to stress evaluated. Correlation coefficients for MCG comparison ranged from 0.3 to 0.5; ECG comparison suggested much less change from stress, ranging from 0.7 to 1.0. Current dipole moment changes at T wave onset were marginal; in contrast, the magnetic dipole moment changed substantially. Since the magnetic dipole reflects vortex currents, changes in its intensity and/or orientation during repolarization suggest this as the biophysical basis of the striking difference in the response of the MCG and ECG to pharmacologic stress. Normal ECG findings at rest and under stress in healthy subjects support the conclusion that the repolarization changes in the MCG were of nonpathologic origin.

Adult↗
PubMed1994

Localization of evoked neuromagnetic 600 Hz activity in the cerebral somatosensory system.

Upon electrical median nerve stimulation wide-band scalp SEP recordings show a burst of high-frequency low-amplitude wavelets of uncertain origin. Digital high-pass filtering (above 400 Hz) of the primary cortical response ("N20") can separate the burst from the underlying "N20 proper" which itself is known to be generated by excitatory postsynaptic potentials (EPSPs) in area 3b. Here, neuromagnetic multichannel recordings show a close correlation between the spatial field distributions of the magnetic burst and of the magnetic "N20m" proper. It is concluded that somatosensory evoked magnetic high-frequency (600 Hz) wavelets have generators at or near the primary somatosensory cortex. Possible modes of generation comprise repetitive discharges conducted in the terminal segments of thalamocortical axons and postsynaptic contributions from neocortical neurons.

Adult↗
PubMed1994

Magnetocardiographic localization of the origin of ventricular ectopic beats.

Magnetocardiographic mapping opens new perspectives for three-dimensional localization of cardiac electrical activation. Using a 37-channel SQUID magnetometer equipment with high shielding, the origin of abnormal ventricular activation was investigated in 18 patients with Wolff-Parkinson-White syndrome prior to catheter ablation and in 5 of 31 patients with coronary artery disease having a sufficient number of monomorphic ventricular extrasystoles to enable evaluation. In all WPW-patients, the site of the earliest delta-wave activation was projected onto the AV-valve plane in accordance with the MR images. The result of magnetocardiographic localization was then compared to the site of successful catheter ablation determined by digital imaging processing. After optimization of the algorithms, both sites were in the various planes at the following distance from each other: X-plane: 0.8 +/- 0.9 cm, Y-plane: 1.1 +/- 1.0 cm and Z-plane: 1.5 +/- 1.0 cm. In three-dimensional projection, the mean difference in space between both positions was calculated to be 2.1 +/- 1.7 cm. After this validation ventricular premature beats were localized in another group of patients. In 4 of 5 patients their origin was found at the border of infarct areas. In each case, the progression of the ventricular activation could be pursued. The detected structure of the magnetic field distribution of the VBP's exhibited a stable bipolar pattern, which is comparable to that of ventricular tachycardia, and its algorithms may be used to localize the origin of ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Non-invasive neuromagnetic monitoring of nerve and muscle injury currents.

Structural damage inflicted on membranes of excitable cells may evoke quasi-DC injury currents driven by the transmembrane resting potential gradient. In contrast to the usually invasive electrophysiological approaches, superconducting quantum interference devices (SQUIDs) measure the concomitant weak biomagnetic fields non-invasively as is shown here for acutely excised rat nerves or muscles. Analysis of the field distributions showed slowly decaying equivalent current dipole moments in the nanoampmeter range as generated by microamp nerve injury currents extending intra-axonally over millimeter distances. The geometric and kinetic parameters of this experimental design may allow in vivo recordings in human patients.

Animals↗