Tilmann Sander

Publications of Tilmann Sander

• The eccentricity effect of inhibition of return is resistant to practice.

  Authors: Yan Bao, Tilmann Sander, Lutz Trahms, Ernst Pöppel, Quan Lei, Bin Zhou

  Neuroscience letters. 06/2011; 500(1):47-51.

  Inhibition of return (IOR) refers to a delayed responding to targets appeared at previously cued location relative to an uncued novel location. In a recent study, Bao and Pöppel reported a functionalInhibition of return (IOR) refers to a delayed responding to targets appeared at previously cued location relative to an uncued novel location. In a recent study, Bao and Pöppel reported a functional dissociation of inhibitory processing in the visual field with much stronger IOR magnitude in the far periphery relative to the perifoveal visual field up to 15° eccentricity. The present study aimed to examine whether this effect is sensitive to participant experience or practice. Consistent with previous findings, our data demonstrated a larger IOR magnitude at 21° relative to 7° stimulus eccentricity. More importantly, no practice-related IOR magnitude changes were observed for both perifoveal and peripheral stimuli, although response times did decrease significantly with practice. These results suggest that the eccentricity effect of IOR is a robust phenomenon which is resistant to practice.

• Processing of visual stimuli in borderline personality disorder: a combined behavioural and magnetoencephalographic study.

  Authors: Angela Merkl, Nina Ammelburg, Sabine Aust, Stefan Roepke, Hans Reinecker, Lutz Trahms, Isabella Heuser, Tilmann Sander

  International journal of psychophysiology : official journal of the International Organization of Psychophysiology. 12/2010; 78(3):257-64.

  Behavioral studies on facial emotion recognition yielded heterogeneous results in patients with Borderline Personality Disorder (BPD). Extrastriate cortex hyperactivation has been demonstrated inBehavioral studies on facial emotion recognition yielded heterogeneous results in patients with Borderline Personality Disorder (BPD). Extrastriate cortex hyperactivation has been demonstrated in imaging studies in patients with BPD during face recognition, but electrophysiological studies are lacking. The aim was to investigate temporal processes following face perception in patients with BPD. Magnetoencephalography (MEG) was used in eleven non-medicated patients with BPD and nine age-matched healthy subjects. Behavioral responses to visual stimuli and an emotion discrimination task were evaluated. First, participants had to silently watch faces, houses and animals. Emotional expressive faces then had to be judged from two basic emotions in a two-alternative forced choice task. Regional field power (RFP) of MEG signals was obtained from two regions of interest: Temporal and occipital areas. Psychometric assessment was performed. Patients with BPD had significantly reduced RFP amplitudes in the right posterior occipital region of interest, for the time window between 150 and 160 ms, irrespective of the type of visual stimulus or the emotional face category. Patients with BPD had significantly higher error rates for recognition of emotional expressive faces compared to healthy controls though they showed a higher accuracy in detecting fearful faces. Controls improved during face recognition, whereas patients showed no learning effect. This MEG study provides evidence for disturbances in cortical visual perception in BPD patients regardless of emotional salience of the stimulus. In line with previous studies subtle deficits in visual perception might be related to impairment in interpersonal communication in BPD.

• Dissociation of summation and peak latencies in visual processing: an MEG study on stimulus eccentricity.

  Authors: Bin Zhou, Yan Bao, Tilmann Sander, Lutz Trahms, Ernst Pöppel

  Neuroscience letters. 10/2010; 483(2):101-4.

  Research on the temporal characteristics of visual processing, as measured with critical flicker fusion or the latency of visual evoked potential (VEP), shows controversial results if differentResearch on the temporal characteristics of visual processing, as measured with critical flicker fusion or the latency of visual evoked potential (VEP), shows controversial results if different eccentricities of visual stimuli are compared. To clarify this question, a direct measure of cortical activity with magnetoencephalography (MEG) was applied to examine the neuronal summation latency and peak latency for both near and far peripheral stimuli. Consistent with cortical magnification, the peak amplitude for less eccentric stimuli was larger than that for more eccentric stimuli. More importantly, the current data also demonstrated longer cortical summation latency and peak latency for more eccentric visual stimuli, but only the summation latency difference between near and far stimuli correlated with the peak amplitude difference between near and far stimuli. These results suggest dissociable mechanisms of summation latency and peak latency with respect to their contributions to the stimulus eccentricity effect, and provide potential explanations for controversial results in previous studies.

• 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.

• MEG/EEG sources of the 170-ms response to faces are co-localized in the fusiform gyrus.

  Authors: Iris Deffke, Tilmann Sander, Jens Heidenreich, Werner Sommer, Gabriel Curio, Lutz Trahms, Andreas Lueschow

  NeuroImage. 06/2007; 35(4):1495-501.

  The 170-ms electrophysiological processing stage (N170 in EEG, M170 in MEG) is considered an important computational step in face processing. Hence its neuronal sources have been modelled in severalThe 170-ms electrophysiological processing stage (N170 in EEG, M170 in MEG) is considered an important computational step in face processing. Hence its neuronal sources have been modelled in several studies. The current study aimed to specify the relation of the dipolar sources underlying N170 and M170. Whole head EEG and MEG were measured simultaneously during the presentation of unfamiliar faces. An Independent Component Analysis (ICA) was applied to the data prior to localization. N170 and M170 were then modelled with a pair of dipoles in a four-shell ellipse (EEG)/homogeneous sphere (MEG) arranged symmetrically across midline. The dipole locations were projected onto the individual structural MR brain images. Dipoles were localized in fusiform gyri in ten out of eleven individuals for EEG and in seven out of eleven for MEG. N170 and M170 were co-localized in the fusiform gyrus in six individuals. The ICA shifted some of the single-subject dipoles up from cerebellum to fusiform gyrus mainly due to the removal of cardiac activity. The group mean dipole locations were also found in posterior fusiform gyri, and did not differ significantly between EEG and MEG. The result was replicated in a repeated measurement 3 months later.

• 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.

• The influence of amplifier, interface and biological noise on signal quality in high-resolution EEG recordings.

  Authors: Hans J Scheer, Tilmann Sander, Lutz Trahms

  Physiological measurement. 03/2006; 27(2):109-17.

  First, the intrinsic random noise sources of a biopotential measurement in general are reviewed. For the special case of an electroencephalographic (EEG) measurement we have extended the commonlyFirst, the intrinsic random noise sources of a biopotential measurement in general are reviewed. For the special case of an electroencephalographic (EEG) measurement we have extended the commonly used amplifier noise model by biological generated background noise. As the strongest of all noise sources involved will dominate the resulting signal to noise ratio (S/N), we have investigated under which conditions this will be the case. We illustrate experimentally that up to 100 Hz S/N practically depends only on cortical generated background noise, while at a few hundred Hz or more amplifier and thermal noise of interelectrode resistance are the major sources.

• Looking for faces: Attention modulates early occipitotemporal object processing.

  Authors: Andreas Lueschow, Tilmann Sander, Stephan G Boehm, Guido Nolte, Lutz Trahms, Gabriel Curio

  Psychophysiology. 06/2004; 41(3):350-60.

  Looking for somebody's face in a crowd is one of the most important examples of visual search. For this goal, attention has to be directed to a well-defined perceptual category. When thisLooking for somebody's face in a crowd is one of the most important examples of visual search. For this goal, attention has to be directed to a well-defined perceptual category. When this categorically selective process starts is, however, still unknown. To this end, we used magnetoencephalography (MEG) recorded over right human occipitotemporal cortex to investigate the time course of attentional modulation of perceptual processes elicited by faces and by houses. The first face-distinctive MEG response was observed at 160-170 ms (M170). Nevertheless, attention did not start to modulate face processing before 190 ms. The first house-distinctive MEG activity was also found around 160-170 ms. However, house processing was not modulated by attention before 280 ms (90 ms later than face processing). Further analysis revealed that the attentional modulation of face processing is not due to later, for example, back-propagated activation of the M170 generator. Rather, subsequent stages of occipitotemporal object processing were modulated in a category-specific manner and with preferential access to face processing.

• Dissociation of summation and peak latencies in visual processing: An MEG study on stimulus eccentricity

  Authors: Bin Zhou, Yan Bao, Tilmann Sander, Lutz Trahms, Ernst Pöppel

  Neuroscience Letters.

  Research on the temporal characteristics of visual processing, as measured with critical flicker fusion or the latency of visual evoked potential (VEP), shows controversial results if differentResearch on the temporal characteristics of visual processing, as measured with critical flicker fusion or the latency of visual evoked potential (VEP), shows controversial results if different eccentricities of visual stimuli are compared. To clarify this question, a direct measure of cortical activity with magnetoencephalography (MEG) was applied to examine the neuronal summation latency and peak latency for both near and far peripheral stimuli. Consistent with cortical magnification, the peak amplitude for less eccentric stimuli was larger than that for more eccentric stimuli. More importantly, the current data also demonstrated longer cortical summation latency and peak latency for more eccentric visual stimuli, but only the summation latency difference between near and far stimuli correlated with the peak amplitude difference between near and far stimuli. These results suggest dissociable mechanisms of summation latency and peak latency with respect to their contributions to the stimulus eccentricity effect, and provide potential explanations for controversial results in previous studies.