Bruno-Marcel Mackert

Publications of Bruno-Marcel Mackert

• Non-invasive simultaneous recording of neuronal and vascular signals in subacute ischemic stroke.

  Authors: Stefanie Leistner, Tilmann Sander-Thoemmes, Heidrun Wabnitz, Michael Moeller, Michaela Wachs, Gabriel Curio, Rainer Macdonald, Lutz Trahms, Bruno-Marcel Mackert

  Biomedizinische Technik. Biomedical engineering. 02/2011; 56(2):85-90.

  In acute focal cerebral ischemia blood flow and neuronal activity change dramatically. A better understanding of the pathophysiological interactions of these two important parameters is limited owingIn acute focal cerebral ischemia blood flow and neuronal activity change dramatically. A better understanding of the pathophysiological interactions of these two important parameters is limited owing to the lack of noninvasive techniques to simultaneously measure these parameters in humans. In this feasibility study, we used DC-magnetoencephalography and near-infrared spectroscopy to find out whether blood flow and neuronal activity as well as neurovascular coupling can be analyzed in patients suffering from subacute ischemic stroke. In a simple motor test condition, six patients with subacute ischemic stroke performed self-paced finger movements (30-s periods of movement, separated by 30-s periods of rest; for a total of 15 min). Combined DC-magnetoencephalography and near-infrared spectroscopy were recorded over the affected and unaffected hemispheres. As a control group, four healthy subjects were investigated. In four out of six patients, the time courses of both signals closely followed the motor task cycles revealing significant differences between movement and rest periods. The vascular signal reached a maximum 1-5 s later than the neuronal signals. This proof-of-principle study demonstrates that it has become feasible to simultaneously and noninvasively monitor neuronal and vascular signal changes in patients in the subacute state of ischemic stroke.

• Clinical characterization of symptomatic microangiopathic brain lesions.

  Authors: Stefanie Leistner, Hans-Christian Koennecke, Jens P Dreier, Anne-Katrin Strempel, Markus Kathke, Alexandrina Nikolova, Peter Heuschman, Uwe Malzahn, Heinrich J Audebert, Bruno-Marcel Mackert

  Frontiers in neurology. 01/2011; 2:61.

  Background: Microangiopathic brain lesions can be separated in diffuse lesions - leukoaraiosis - and focal lesions - lacunes. Leukoaraiosis and lacunes are caused by common cerebrovascular riskBackground: Microangiopathic brain lesions can be separated in diffuse lesions - leukoaraiosis - and focal lesions - lacunes. Leukoaraiosis and lacunes are caused by common cerebrovascular risk factors, but whether they represent a common entity is not sufficiently investigated. The present study aimed to determine the clinical profiles associated with the extent of leukoaraiosis and lacunes. Methods: Sixty-four consecutive patients with acute microangiopathic stroke were studied. Leukoaraiosis and lacunes were stratified according to their MRI-based extent. Standardized clinical assessment included clinical syndromes, cerebrovascular risk factors, cognitive performance, retinal imaging, ultrasonography, blood, and urine parameters. Results: Different clinical profiles for leukoaraiosis and lacunes were found. Regarding leukoaraiosis, the cognitive scores (SISCO, mini mental score examination, mental examination) and the presence of hyperlipidemia decreased as the severity of leukoaraiosis increased. Univariate and multivariate analysis revealed that these cognitive score values as well as the presence of hyperlipidemia correlated significantly with no or only mild leukoaraiosis. Regarding lacunes, the percentage of migraine, previous stroke events, hydrocephalus, left ventricular hypertrophy, and a higher National Institutes of Health Stroke Scale increased as the number of lacunar lesions increased. Statistical analysis revealed that these parameters correlated not significantly with the number of lacunes. Conclusions: The findings suggests that leukoaraiosis and lacunes are different microangiopathic entities potentially requiering different treatment concepts.

• Magnetoencephalography discriminates modality-specific infraslow signals less than 0.1 Hz.

  Authors: Stefanie Leistner, Tilmann H Sander, Gerd Wuebbeler, Alfred Link, Clemens Elster, Gabriel Curio, Lutz Trahms, Bruno-Marcel Mackert

  Neuroreport. 02/2010; 21(3):196-200.

  DC-magnetoencephalography (DC-MEG) technique has been refined and allows to record cortical activity in the infraslow frequency range less than 0.1 Hz noninvasively. Important questions however,DC-magnetoencephalography (DC-MEG) technique has been refined and allows to record cortical activity in the infraslow frequency range less than 0.1 Hz noninvasively. Important questions however, remained, especially, how specific these infraslow activations can be recorded and whether different activations, for example, motor versus acoustic, can be separated. To clarify these questions, in the present DC-MEG study, cortical infraslow activity was investigated intraindividually in response to different activation modalities, that is, motor versus acoustic: in 13 individuals, 30-s periods of finger movement or listening to concert music, were interleaved for 60 min. DC-MEG was capable to resolve intermodal differences concerning the relative amplitudes, field patterns, and source localizations. These results clarify that DC-MEG allows to identify and to discriminate modality-specific infraslow cortical neuronal signals.

• Cross-Correlation of Motor Activity Signals from dc-Magnetoencephalography, Near-Infrared Spectroscopy, and Electromyography.

  Authors: Tilmann Heinrich Sander, Stefanie Leistner, Heidrun Wabnitz, Bruno-Marcel Mackert, Rainer Macdonald, Lutz Trahms

  Comp. Int. and Neurosc. 01/2010; 2010.

• Cross-correlation of motor activity signals from dc-magnetoencephalography, near-infrared spectroscopy, and electromyography.

  Authors: Tilmann H Sander, Stefanie Leistner, Heidrun Wabnitz, Bruno-Marcel Mackert, Rainer Macdonald, Lutz Trahms

  Computational intelligence and neuroscience. 01/2010;

  Neuronal and vascular responses due to finger movements were synchronously measured using dc-magnetoencephalography (dcMEG) and time-resolved near-infrared spectroscopy (trNIRS). The finger movementsNeuronal and vascular responses due to finger movements were synchronously measured using dc-magnetoencephalography (dcMEG) and time-resolved near-infrared spectroscopy (trNIRS). The finger movements were monitored with electromyography (EMG). Cortical responses related to the finger movement sequence were extracted by independent component analysis from both the dcMEG and the trNIRS data. The temporal relations between EMG rate, dcMEG, and trNIRS responses were assessed pairwise using the cross-correlation function (CCF), which does not require epoch averaging. A positive lag on a scale of seconds was found for the maximum of the CCF between dcMEG and trNIRS. A zero lag is observed for the CCF between dcMEG and EMG. Additionally this CCF exhibits oscillations at the frequency of individual finger movements. These findings show that the dcMEG with a bandwidth up to 8 Hz records both slow and faster neuronal responses, whereas the vascular response is confirmed to change on a scale of seconds.

• Differential Infraslow (<0.1 Hz) Cortical Activations in the Affected and Unaffected Hemispheres From Patients With Subacute Stroke Demonstrated by Noninvasive DC-Magnetoencephalography.

  Authors: Stefanie Leistner, Tilmann Sander, Michaela Wachs, Martin Burghoff, Gabriel Curio, Lutz Trahms, Bruno-Marcel Mackert

  Stroke; a journal of cerebral circulation. 03/2009;

  BACKGROUND AND PURPOSE: Sustained mass depolarization of neurons, termed cortical spreading depolarization, is one electrophysiological correlate of the ischemic injury of neurons. Cortical spreadingBACKGROUND AND PURPOSE: Sustained mass depolarization of neurons, termed cortical spreading depolarization, is one electrophysiological correlate of the ischemic injury of neurons. Cortical spreading depolarizations spread in the gray matter at a rate of approximately 3 mm/min and are associated with large infraslow extracellular potential changes (<0.05 Hz). Moreover, smaller infraslow potential changes accompany functional activation and might help to assess neuronal repair after stroke. The objective of the present pilot study was to investigate whether it is feasible to apply noninvasive near-DC-magnetoencephalography to detect and monitor infraslow field changes in patients with acute stroke. METHODS: A simple motor condition was used to induce physiological cortical infraslow field changes. Five patients in a subacute state after ischemic stroke performed self-paced simple finger movements (30-second periods of finger movements, always separated by 30-second periods of rest, for a total of 15 minutes). Near-DC-magnetoencephalography signals were recorded over the contralateral primary motor cortex for the affected and unaffected hemisphere, respectively. RESULTS: In all patients, the time courses of the contralateral cortical field amplitudes in the infraslow frequency range followed closely the motor task cycles revealing statistically significant differences between finger movement and rest periods. In 4 of 5 patients, infraslow field amplitudes were significantly stronger over the unaffected hemisphere compared with the affected hemisphere. CONCLUSIONS: This study demonstrates that cortical infraslow activity can be recorded noninvasively in patients in the subacute state after ischemic stroke. It is suggested that near-DC-magnetoencephalography is a promising tool to also detect cortical spreading depolarization noninvasively.

• Dynamics of cortical neurovascular coupling analyzed by simultaneous DC-magnetoencephalography and time-resolved near-infrared spectroscopy.

  Authors: Bruno-Marcel Mackert, Stefanie Leistner, Tilmann Sander, Adam Liebert, Heidrun Wabnitz, Martin Burghoff, Lutz Trahms, Rainer Macdonald, Gabriel Curio

  NeuroImage. 03/2008; 39(3):979-86.

  Functional magnetic resonance imaging (fMRI) visualizes activated brain areas with a high spatial resolution. The activation signal is determined by the local change of cerebral blood oxygenation,Functional magnetic resonance imaging (fMRI) visualizes activated brain areas with a high spatial resolution. The activation signal is determined by the local change of cerebral blood oxygenation, blood volume and blood flow which serve as surrogate marker for the neuronal signal itself. Here, the complex coupling between these parameters and the electrophysiologic activity is characterized non-invasively in humans during a simple motor task using simultaneously DC-magnetoencephalography (DC-MEG), for the detection of neuronal signals, and time-resolved near-infrared spectroscopy (trNIRS), for cortical metabolic/vascular responses: over the left primary motor cortex hand area of healthy subjects DC-fields and trNIRS parameters followed closely the 30 s motor task cycles, i.e., finger movements of the right hand alternating with rest. In subjects showing a sufficient signal-to-noise ratio the analysis of variance of photon time of flight proved that the task-related trNIRS changes originated from the cortex. While onset and relaxation started simultaneously, trNIRS signals reached 50% of the maximum level 1-4 s later than the DC-MEG-signals. The non-invasive 'dual' setup helps to characterize simultaneously the two complementary aspects of the 'hemodynamic inverse problem', i.e., the coupling of neuronal and vascular/metabolic signals, in healthy subjects and provides a new analysis perspective for pathophysiological coupling concepts in diverse diseases, e.g., in stroke, hypertension and Alzheimer's disease.

• Combined MEG and EEG methodology for non-invasive recording of infraslow activity in the human cortex.

  Authors: Stefanie Leistner, Tilmann Sander, Martin Burghoff, Gabriel Curio, Lutz Trahms, Bruno-Marcel Mackert

  Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. 01/2008; 118(12):2774-80.

  OBJECTIVE: Periinfarct depolarisation and spreading depression represent key mechanisms of neuronal injury after stroke. Changes in cortical electrical potentials and magnetic fields in the very lowOBJECTIVE: Periinfarct depolarisation and spreading depression represent key mechanisms of neuronal injury after stroke. Changes in cortical electrical potentials and magnetic fields in the very low frequency range are relevant parameters to characterize these events, which up to now have only been recorded invasively. In this study, we proved whether a non-invasive combined MEG/EEG recording technique is able to quantitatively monitor cortical infraslow activity in humans. METHODS: We used repetitive very slow and slow right finger movements as a physiological motor activation paradigm to induce cortical infraslow activity. Infraslow fields were recorded over the left hemisphere using a modulation-based MEG technique. EEG was performed using 16 standard Ag-Cl electrodes that covered the left motor cortex. RESULTS: We recorded stable focal motor-related infraslow magnetic field changes in seven out of seven subjects. We also found correlating infraslow electrical potential changes in three out of seven subjects. Slow finger movements generated significantly stronger field and potential changes than very slow movements. CONCLUSIONS: This study demonstrates the technical feasibility of combined non-invasive electrical potential and magnetic field measurements to localize and quantitatively monitor physiological, low amplitude, infraslow cortical activity in humans. This specific combination of simultaneous recording techniques allows to benefit from the specific physical advantages of each method. SIGNIFICANCE: This combined non-invasive MEG-EEG methodology is able to provide important information on infraslow neuronal activity originating from tangentially and radially oriented sources. Moreover, this dual approach has the potential to separate neuronal from non-neuronal DC-sources, e.g., radially to the head orientated DC-currents across the skin/scalp/skull/dura occurring during cerebral hypercapnia or hypoxia.

• Recording of focal direct current (DC) changes in the human cerebral cortex using refined non-invasive DC-EEG methodology.

  Authors: Stefanie Leistner, Hans-Juergen Scheer, Tilmann Sander, Martin Burghoff, Lutz Trahms, Gabriel Curio, Bruno-Marcel Mackert

  Biomedizinische Technik. Biomedical engineering. 01/2007; 52(1):102-5.

  A non-invasive DC electroencephalographic (DC-EEG) method was developed to record and analyze focal low-frequency (<0.1 Hz) DC changes in the human cerebral cortex. A simple repetitiveA non-invasive DC electroencephalographic (DC-EEG) method was developed to record and analyze focal low-frequency (<0.1 Hz) DC changes in the human cerebral cortex. A simple repetitive finger-movement task was used as a physiological activation paradigm. DC-EEG amplitudes were recorded using a custom-made DC amplifier with automatic offset correction. A total of 16 standard Ag/AgCl electrodes covered the left primary motor cortex. In three of six subjects, reliable focal motor-related DC-EEG shifts over the hand cortex were monitored. This study demonstrates that refined DC-EEG recording and data analysis procedures allow non-invasive recording of low-frequency and low-amplitude focal cortical changes in humans. An important clinical perspective of this technology is the detection of stroke-associated cortical DC activity.

• Tonic neuronal activation during simple and complex finger movements analyzed by DC-magnetoencephalography.

  Authors: Stefanie Leistner, Gerd Wuebbeler, Lutz Trahms, Gabriel Curio, Bruno-Marcel Mackert

  Neuroscience letters. 03/2006; 394(1):42-7.

  Functional neuroimaging techniques map neuronal activation indirectly via local concomitant cortical vascular/metabolic changes. In a complementary approach, DC-magnetoencephalography measuresFunctional neuroimaging techniques map neuronal activation indirectly via local concomitant cortical vascular/metabolic changes. In a complementary approach, DC-magnetoencephalography measures neuronal activation dynamics directly, notably in a time range of the slow vascular/metabolic response. Here, using this technique neuronal activation dynamics and patterns for simple and complex finger movements are characterized intraindividually: in 6/6 right-handed subjects contralateral prolonged (30 s each) complex self-paced sequential finger movements revealed stronger field amplitudes over the pericentral sensorimotor cortex than simple movements. A consistent lateralization for contralateral versus ipsilateral finger movements was not found (4/6). A subsequent sensory paradigm focused on somatosensory afferences during the motor tasks and the reliability of the measuring technique. In all six subjects stable sustained neuronal activation during electrical median nerve stimulation was recorded. These neuronal quasi-tonic activation characteristics provide a new non-invasive neurophysiological measure to interpret signals mapped by functional neuroimaging techniques.

• Hemosiderin deposits in chronic graft-vs.-host disease related myopathy.

  Authors: Martin Schmidt-Hieber, Ali Fuat Okuducu, Gisela Stoltenburg, Bruno-Marcel Mackert, Nadia Benzian, Eckhard Thiel, Igor Wolfgang Blau

  European journal of haematology. 01/2006; 75(6):522-6.

  Chronic graft-vs.-host disease (cGVHD) occurs in 20-50% of patients who survive for at least 100 d after allogeneic stem cell transplantation (SCT). cGVHD includes scleroderma-like skin changes,Chronic graft-vs.-host disease (cGVHD) occurs in 20-50% of patients who survive for at least 100 d after allogeneic stem cell transplantation (SCT). cGVHD includes scleroderma-like skin changes, chronic cholangitis, obstructive lung disease and general wasting syndrome. Polymyositis or myopathy are rare manifestations of cGVHD with approximately 40 reported cases. Polymyositis accompanied by hemosiderin deposits in cGVHD has been reported only once, and there are no reports on lipofuscin deposits in skeletal muscle cells in cGVHD. We report here on a 56-yr-old male who underwent allogeneic SCT in 1999 for osteomyelofibrosis and progressive hematopoietic insufficiency. In February 2004, the patient was hospitalized for progressive muscular weakness with loss of the ability to walk. Laboratory tests demonstrated normal values for serum creatine kinase, aldolase and lactic dehydrogenase; the ferritin level was highly elevated. The femoral muscle biopsy showed mostly perifascicular atrophy as well as numerous subsarcolemmal hemosiderin and lipofuscin deposits. Intravenous administration of the chelating agent deferoxamine was ineffective. Three weeks later the patient died of aspiration pneumonia. Interestingly, autopsy disclosed moderate hemosiderin deposits in the liver, the organ usually involved in hemosiderosis.

• Magnetoneurography: theory and application to peripheral nerve disorders.

  Authors: Bruno-Marcel Mackert

  Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. 01/2005; 115(12):2667-76.

  Magnetoneurography (MNG) is a non-invasive method to trace and visualize three-dimensionally the propagation path of compound action currents (CAC) along peripheral nerves. The basic physical andMagnetoneurography (MNG) is a non-invasive method to trace and visualize three-dimensionally the propagation path of compound action currents (CAC) along peripheral nerves. The basic physical and physiological principle is the mapping of extremely weak magnetic fields generated by the intraaxonal longitudinal ion flows of evoked nerval CAC using SQUID sensors (Superconducting Quantum Interference Devices). During recent years, MNG protocols have been established which allow for a non-invasive spatiotemporal tracing of impulse propagation along peripheral nerves in humans and in particular along proximal nerve segments in a clinical setting. Thereby, the three-dimensional path, the local nerve conduction velocity, the length and strength of the CAC de- and repolarization phase have been reconstructed. First recordings in patients demonstrated that the method is sensitive enough to detect and to localize nerve conduction anomalities along nerve roots, as, e.g. caused by lumbosacral disc herniation. This review on MNG will focus on those studies which provide data from humans and thereby reveal perspectives for its future clinical applications.

• Non-invasive magnetic detection of human injury currents.

  Authors: Maren Carbon, Gerd Wübbeler, Bruno-Marcel Mackert, Jan Mackert, Josef Ramsbacher, Lutz Trahms, Gabriel Curio

  Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. 06/2004; 115(5):1027-32.

  OBJECTIVE: Injury currents are a hallmark of acute lesions in polarized cells. Our objective was to develop a non-invasive technique for monitoring human near-DC injury currents in vivo. METHODS:OBJECTIVE: Injury currents are a hallmark of acute lesions in polarized cells. Our objective was to develop a non-invasive technique for monitoring human near-DC injury currents in vivo. METHODS: Using diagnostic muscle biopsy as controlled paradigm, injury-related magnetic DC-fields were mapped for 60 min postsurgery over leg muscle lesions of 9 subjects. A 49-channel magnetometer was used in combination with a mechanical horizontal modulation of the subject beneath the sensor array. RESULTS: Magnetic DC-field maps showed salient differences between biopsy and contralateral legs in 8/9 patients with a characteristic slowly decaying field in all biopsy legs. A variety of anomalous DC-field patterns was recorded over the biopsy sites, corresponding to theoretically predicted geometric variations of equivalent DC-current dipoles, i.e. wound surfaces, pointing into opposing muscle fibre ends. By contrast, all control measurements showed an elongated dipolar DC-field pattern. Additionally, mean global DC-field strengths were significantly higher over biopsy legs compared to the contralateral site. CONCLUSIONS: Our pilot data illustrate that human injury currents can be detected using non-invasive magnetometry. Thus, DC-magnetometry may provide an essential new tool for clinical monitoring of injury currents, possibly also in brain tissue, e.g. in case of anoxic or peri-infarct depolarizations.

• Neurovascular coupling analyzed non-invasively in the human brain.

  Authors: Bruno-Marcel Mackert, Gerd Wübbeler, Stefanie Leistner, Kamil Uludag, Hellmuth Obrig, Arno Villringer, Lutz Trahms, Gabriel Curio

  Neuroreport. 02/2004; 15(1):63-6.

  Most functional brain imaging methods detect neuronal activations indirectly through the accompanying neurovascular response. Here, we demonstrate that a novel methodological approach, theMost functional brain imaging methods detect neuronal activations indirectly through the accompanying neurovascular response. Here, we demonstrate that a novel methodological approach, the combination of DC-magnetoencephalography (DC-MEG) and near-infrared spectroscopy (NIRS), allows non-invasive assessment of the dynamics of neurovascular coupling in the human brain: detecting directly slow neuronal processes (with time constants of 30s), DC-MEG revealed, even in unaveraged recordings, sustained neuronal activations at pericentral hand cortices contralateral to repetitive finger movements; these were accompanied by the ensuing local vascular response showing similar dynamical features as quantified by simultaneously recorded NIRS. This non-invasive approach opens a new avenue for the understanding of neurovascular coupling during physiological tasks as well as in diseases involving slow neuronal depolarization shifts and alterations of blood flow, such as stroke or migraine.

• The eloquence of silent cortex: analysis of afferent input to deafferented cortex in arm amputees.

  Authors: Bruno-Marcel Mackert, Tanja Sappok, Sabine Grüsser, Herta Flor, Gabriel Curio

  Neuroreport. 04/2003; 14(3):409-12.

  Cortical reorganisation after limb amputation includes topographic displacements of body representation areas and changes of areal extent. Remarkably, truncated nerves, which had innervated amputatedCortical reorganisation after limb amputation includes topographic displacements of body representation areas and changes of areal extent. Remarkably, truncated nerves, which had innervated amputated limb parts and remained in the residual limbs, can retain access to the deafferented somatosensory cortex. Using somatosensory evoked potentials (SEP) we characterized afferences from electrically stimulated truncated nerves to the brachial plexus and cortex in 12 arm amputees. While peripheral responses were highly variable, thalamocortical input to S-1, as reflected by the primary cortical SEP component, was present in 11 of 12 patients. Despite long-term deafferentation, macroscopic phenomena of inhibition/refractoriness, as assessed by stimulus rate variations, appeared to be changed only marginally. Thus, deafferented cortex remains responsive when given artificial phantom input and could provide a neuronal substrate for spontaneous phantom limb sensations, including phantom pain.

• SQUID measurements of human nerve and muscle near-DC injury-currents using a mechanical modulation of the source position

  Authors: Andreas Ziehe, Bruno-Marcel Mackert, Lutz Trahms, Gabriel Curio

  08/2000;

  | We apply a recently developed multi-variate statistical data analysis technique - so called blind source separation by independent component analysis - to process MEG recordings of near-DC fields.| We apply a recently developed multi-variate statistical data analysis technique - so called blind source separation by independent component analysis - to process MEG recordings of near-DC fields. The extraction of nearDC fields from MEG recordings has great relevance for medical applications since slowly varying DC-phenomena have been found e.g. in cerebral anoxia and spreading depression in animals. Comparing several blind source separation approaches, it turns out that an algorithm based on temporal decorrelation successfully extracted a DC-component which was induced in the auditory cortex by presentation of music. The task is challenging because of the limited amount of available data and the corruption by outliers, which makes it an interesting real-world testbed for studying the robustness of ICA methods. Keywords| Biomagnetism, biomedical data processing, blind source separation, DC-recordings, independent component analysis, magnetoencephalography (MEG). I. Introduction Rec...

• Independent Component Analysis of Non-invasively Recorded Cortical Magnetic DC-fields in Humans

  Authors: Andreas Ziehe, Guido Nolte, Bruno-Marcel Mackert, Gabriel Curio, Gmd Forschungszentrum, Informationstechnik Gmbh, Schlo Birlinghoven

  01/1999;

  Artifacts in magnetoneurography (MNG) data due to endogenous biological noise sources, e.g. heart signal, can be four orders of magnitude higher than the signal of interest. Therefore it is importantArtifacts in magnetoneurography (MNG) data due to endogenous biological noise sources, e.g. heart signal, can be four orders of magnitude higher than the signal of interest. Therefore it is important to establish effective artifact reduction methods. We propose a blind source separation algorithm using only second order temporal correlations for cleaning bio-magnetic measurements of evoked responses in the peripheral nervous system. The algorithm showed its efficiency by eliminating disturbances originating from biological and technical noise sources and successfully extracting the signal of interest. This yields a significant improvement of the neuro-magnetic source analysis. Keywords Biomedical data processing, Artifact reduction, Biomagnetism, Magnetoneurography, Blind source separation, Independent component analysis. Acknowledgment We acknowledge valuable discussions with members of the Biophysics Group at PhysikalischTechnische Bundesanstalt (PTB) Berlin. All MNG studies were p...

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

  Authors: Gabriel Curio, Bruno-Marcel Mackert, Martin Burghoff, Joachim Neumann, Guido Nolte, Michael Scherg, Peter Marx

  Neuroscience Letters.

  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 msBased 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.

• Rapid recovery (20 ms) of human 600 Hz electroencephalographic wavelets after double stimulation of sensory nerves

  Authors: Bruno-Marcel Mackert, Simon Weisenbach, Guido Nolte, Gabriel Curio

  Neuroscience Letters.

  Non-invasive scalp-recordings of human somatosensory evoked potentials (SEP) contain high-frequency (600 Hz) wavelet bursts, presumably generated by synchronized thalamocortical and/or intracorticalNon-invasive scalp-recordings of human somatosensory evoked potentials (SEP) contain high-frequency (600 Hz) wavelet bursts, presumably generated by synchronized thalamocortical and/or intracortical population spikes. Here, double pulse stimulation (interval 20 ms) in 12 healthy subjects revealed significantly different burst recovery for mixed vs. sensory-only nerves. For median nerves the second burst response was decreased (11/11 subjects), possibly due to interfering reafferent (e.g. muscle spindle) input. In contrast, for sensory-only superficial radial nerves (containing less fibers than median nerves), weak bursts were detected in 6/11 subjects and were found fully recovered in 4/6 subjects. This potential for rapid burst recovery at 20 ms intervals renders contributions from neurons emitting bursts based on slowly recovering low-threshold calcium spikes unlikely and favors the generation of macroscopic SEP bursts by specialized cell populations, e.g. inhibitory interneurons and/or chattering cells the latter of which are capable to discharge rapidly repeating (50 Hz) high-frequency (600 Hz) bursts of fast sodium spikes.

• Tracing of proximal lumbosacral nerve conduction – a comparison of simultaneous magneto – and electroneurography

  Authors: Bruno-Marcel Mackert, Martin Burghoff, Lars-Henning Hiss, Lutz Trahms, Gabriel Curio

  Clinical Neurophysiology.

  Objective: The reconstruction of nerve impulse conduction along proximal lumbosacral plexus and nerve roots is compared using simultaneous magneto- and electroneurography.Methods: In 3 healthyObjective: The reconstruction of nerve impulse conduction along proximal lumbosacral plexus and nerve roots is compared using simultaneous magneto- and electroneurography.Methods: In 3 healthy subjects the left tibial nerve was electrostimulated at the ankle. Evoked magnetic fields and electric surface potentials were measured simultaneously over the lumbosacral spine using a multichannel SQUID-detector with a planar measuring area and 25 surface electrodes covering a comparable area centered around L4. Based on either magnetic field or electric potential maps the depolarization front of the evoked compound action currents (CAC) was spatio-temporally reconstructed using a simple equivalent current dipole model in a half-space volume conductor.Results: The mean signal-to-noise ratio in the magnetic (electric) recordings was around 4 (8). Yet, the localization quality for the propagating CAC was lower for electric than magnetic recordings. The local nerve conduction velocity was around 47 m/s (calculated from magnetic data), but fluctuated unphysiologically for electric data.Conclusion: In comparison to electroneurography, an anatomically reasonable localization of evoked compound action currents propagating in lumbosacral roots can be obtained by magnetoneurography.