Jürgen Dammers

Publications (29) View all

• Source

  Available from: Jürgen Dammers

  Article: Automatic identification of gray and white matter components in polarized light imaging.

  Jürgen Dammers, Lukas Breuer, Markus Axer, Melanie Kleiner, Björn Eiben, David Grässel, Timo Dickscheid, Karl Zilles, Katrin Amunts, N Joni Shah, Uwe Pietrzyk
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  ABSTRACT: Polarized light imaging (PLI) enables the visualization of fiber tracts with high spatial resolution in microtome sections of postmortem brains. Vectors of the fiber orientation defined by inclination and direction angles can directly be derived from the optical signals employed by PLI analysis. The polarization state of light propagating through a rotating polarimeter is varied in such a way that the detected signal of each spatial unit describes a sinusoidal signal. Noise, light scatter and filter inhomogeneities, however, interfere with the original sinusoidal PLI signals, which in turn have direct impact on the accuracy of subsequent fiber tracking. Recently we showed that the primary sinusoidal signals can effectively be restored after noise and artifact rejection utilizing independent component analysis (ICA). In particular, regions with weak intensities are greatly enhanced after ICA based artifact rejection and signal restoration. Here, we propose a user independent way of identifying the components of interest after decomposition; i.e., components that are related to gray and white matter. Depending on the size of the postmortem brain and the section thickness, the number of independent component maps can easily be in the range of a few ten thousand components for one brain. Therefore, we developed an automatic and, more importantly, user independent way of extracting the signal of interest. The automatic identification of gray and white matter components is based on the evaluation of the statistical properties of the so-called feature vectors of each individual component map, which, in the ideal case, shows a sinusoidal waveform. Our method enables large-scale analysis (i.e., the analysis of thousands of whole brain sections) of nerve fiber orientations in the human brain using polarized light imaging.
  NeuroImage 08/2011; 59(2):1338-47. · 5.89 Impact Factor
• Article: A novel approach to the human connectome: ultra-high resolution mapping of fiber tracts in the brain.

  Markus Axer, Katrin Amunts, David Grässel, Christoph Palm, Jürgen Dammers, Hubertus Axer, Uwe Pietrzyk, Karl Zilles
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  ABSTRACT: Signal transmission between different brain regions requires connecting fiber tracts, the structural basis of the human connectome. In contrast to animal brains, where a multitude of tract tracing methods can be used, magnetic resonance (MR)-based diffusion imaging is presently the only promising approach to study fiber tracts between specific human brain regions. However, this procedure has various inherent restrictions caused by its relatively low spatial resolution. Here, we introduce 3D-polarized light imaging (3D-PLI) to map the three-dimensional course of fiber tracts in the human brain with a resolution at a submillimeter scale based on a voxel size of 100 μm isotropic or less. 3D-PLI demonstrates nerve fibers by utilizing their intrinsic birefringence of myelin sheaths surrounding axons. This optical method enables the demonstration of 3D fiber orientations in serial microtome sections of entire human brains. Examples for the feasibility of this novel approach are given here. 3D-PLI enables the study of brain regions of intense fiber crossing in unprecedented detail, and provides an independent evaluation of fiber tracts derived from diffusion imaging data.
  NeuroImage 01/2011; 54(2):1091-101. · 5.89 Impact Factor
• Article: Neuromagnetic oscillations to emotional faces and prosody.

  Yu-Han Chen, J Christopher Edgar, Tom Holroyd, Jürgen Dammers, Heike Thönnessen, Timothy P L Roberts, Klaus Mathiak
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  ABSTRACT: Higher association cortices as well as unisensory areas can support multisensory integration [D. Senkowski et al. (2008) Trends Neurosci., 31, 401-409]. The present study investigated whether audiovisual integration of emotional information emerges early at unisensory or later at higher association cortices. Emotional stimuli were presented in three blocks: audiovisual (AV), auditory (A) and visual (V). Eighteen participants performed a delayed emotional recognition task (happy, angry or neutral prosody and/or facial expression) while whole-brain magnetoencephalography (MEG) data were obtained. Time-frequency evoked and total power analyses were performed on the sensor data, and source localization of the frequencies of interest performed via a synthetic aperture magnetometry beamformer. To examine crossmodal integration between bimodal and unimodal conditions, two contrasts were specified: AV > A and AV > V. In the AV > A contrast, early effects were observed on both the temporal and the occipital evoked responses. However, at the source level, early alpha suppression was limited to the occipital sources without changes in temporal cortices. In the AV > V contrast, sensor and source findings revealed increased alpha suppression only in temporal cortices, with no changes in visual cortex. Thus, no crossmodal effect in unisensory areas emerged. Instead, increased frontal alpha activity in both the AV > A and AV > V contrasts supports the view that affective information from face and prosody converges at higher association cortices.
  European Journal of Neuroscience 05/2010; 31(10):1818-27. · 3.63 Impact Factor
• Source

  Available from: Christoph Palm

  Article: Towards ultra-high resolution fibre tract mapping of the human brain - registration of polarised light images and reorientation of fibre vectors.

  Christoph Palm, Markus Axer, David Gräßel, Jürgen Dammers, Johannes Lindemeyer, Karl Zilles, Uwe Pietrzyk, Katrin Amunts
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  ABSTRACT: Polarised light imaging (PLI) utilises the birefringence of the myelin sheaths in order to visualise the orientation of nerve fibres in microtome sections of adult human post-mortem brains at ultra-high spatial resolution. The preparation of post-mortem brains for PLI involves fixation, freezing and cutting into 100-mum-thick sections. Hence, geometrical distortions of histological sections are inevitable and have to be removed for 3D reconstruction and subsequent fibre tracking. We here present a processing pipeline for 3D reconstruction of these sections using PLI derived multimodal images of post-mortem brains. Blockface images of the brains were obtained during cutting; they serve as reference data for alignment and elimination of distortion artefacts. In addition to the spatial image transformation, fibre orientation vectors were reoriented using the transformation fields, which consider both affine and subsequent non-linear registration. The application of this registration and reorientation approach results in a smooth fibre vector field, which reflects brain morphology. PLI combined with 3D reconstruction and fibre tracking is a powerful tool for human brain mapping. It can also serve as an independent method for evaluating in vivo fibre tractography.
  Frontiers in Human Neuroscience 01/2010; 4:9. · 2.34 Impact Factor
• Source

  Available from: Christine Norra

  Article: Early sensory encoding of affective prosody: neuromagnetic tomography of emotional category changes.

  Heike Thönnessen, Frank Boers, Jürgen Dammers, Yu-Han Chen, Christine Norra, Klaus Mathiak
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  ABSTRACT: In verbal communication, prosodic codes may be phylogenetically older than lexical ones. Little is known, however, about early, automatic encoding of emotional prosody. This study investigated the neuromagnetic analogue of mismatch negativity (MMN) as an index of early stimulus processing of emotional prosody using whole-head magnetoencephalography (MEG). We applied two different paradigms to study MMN; in addition to the traditional oddball paradigm, the so-called optimum design was adapted to emotion detection. In a sequence of randomly changing disyllabic pseudo-words produced by one male speaker in neutral intonation, a traditional oddball design with emotional deviants (10% happy and angry each) and an optimum design with emotional (17% happy and sad each) and nonemotional gender deviants (17% female) elicited the mismatch responses. The emotional category changes demonstrated early responses (<200 ms) at both auditory cortices with larger amplitudes at the right hemisphere. Responses to the nonemotional change from male to female voices emerged later ( approximately 300 ms). Source analysis pointed at bilateral auditory cortex sources without robust contribution from other such as frontal sources. Conceivably, both auditory cortices encode categorical representations of emotional prosodic. Processing of cognitive feature extraction and automatic emotion appraisal may overlap at this level enabling rapid attentional shifts to important social cues.
  NeuroImage 12/2009; 50(1):250-9. · 5.89 Impact Factor