Susanne Holtze

Publications of Susanne Holtze

• Somatosensory activation of two fingers can be discriminated with ultrahigh-density diffuse optical tomography.

  Authors: Christina Habermehl, Susanne Holtze, Jens Steinbrink, Stefan P Koch, Hellmuth Obrig, Jan Mehnert, Christoph H Schmitz

  NeuroImage. 12/2011; 59(4):3201-11.

  Topographic non-invasive near infrared spectroscopy (NIRS) has become a well-established tool for functional brain imaging. Applying up to 100 optodes over the head of a subject, allows achieving aTopographic non-invasive near infrared spectroscopy (NIRS) has become a well-established tool for functional brain imaging. Applying up to 100 optodes over the head of a subject, allows achieving a spatial resolution in the centimeter range. This resolution is poor compared to other functional imaging tools. However, recently it was shown that diffuse optical tomography (DOT) as an extension of NIRS based on high-density (HD) probe arrays and supplemented by an advanced image reconstruction procedure allows describing activation patterns with a spatial resolution in the millimeter range. Building on these findings, we hypothesize that HD-DOT may render very focal activations accessible which would be missed by the traditionally used sparse arrays. We examined activation patterns in the primary somatosensory cortex, since its somatotopic organization is very fine-grained. We performed a vibrotactile stimulation study of the first and fifth finger in eight human subjects, using a 900-channel continuous-wave DOT imaging system for achieving a higher resolution than conventional topographic NIRS. To compare the results to a well-established high-resolution imaging technique, the same paradigm was investigated in the same subjects by means of functional magnetic resonance imaging (fMRI). In this work, we tested the advantage of ultrahigh-density probe arrays and show that highly focal activations would be missed by classical next-nearest neighbor NIRS approach, but also by DOT, when using a sparse probe array. Distinct activation patterns for both fingers correlated well with the expected neuroanatomy in five of eight subjects. Additionally we show that activation for different fingers is projected to different tissue depths in the DOT image. Comparison to the fMRI data yielded similar activation foci in seven out of ten finger representations in these five subjects when comparing the lateral localization of DOT and fMRI results.

• High-resolution optical functional mapping of the human somatosensory cortex.

  Authors: Stefan P Koch, Christina Habermehl, Jan Mehnert, Christoph H Schmitz, Susanne Holtze, Arno Villringer, Jens Steinbrink, Hellmuth Obrig

  Frontiers in neuroenergetics. 01/2010; 2:12.

  Non-invasive optical imaging of brain function has been promoted in a number of fields in which functional magnetic resonance imaging (fMRI) is limited due to constraints induced by the scanningNon-invasive optical imaging of brain function has been promoted in a number of fields in which functional magnetic resonance imaging (fMRI) is limited due to constraints induced by the scanning environment. Beyond physiological and psychological research, bedside monitoring and neurorehabilitation may be relevant clinical applications that are yet little explored. A major obstacle to advocate the tool in clinical research is insufficient spatial resolution. Based on a multi-distance high-density optical imaging setup, we here demonstrate a dramatic increase in sensitivity of the method. We show that optical imaging allows for the differentiation between activations of single finger representations in the primary somatosensory cortex (SI). Methodologically our findings confirm results in a pioneering study by Zeff et al. (2007) and extend them to the homuncular organization of SI. After performing a motor task, eight subjects underwent vibrotactile stimulation of the little finger and the thumb. We used a high-density diffuse-optical sensing array in conjunction with optical tomographic reconstruction. Optical imaging disclosed three discrete activation foci one for motor and two discrete foci for vibrotactile stimulation of the first and fifth finger, respectively. The results were co-registered to the individual anatomical brain anatomy (MRI) which confirmed the localization in the expected cortical gyri in four subjects. This advance in spatial resolution opens new perspectives to apply optical imaging in the research on plasticity notably in patients undergoing neurorehabilitation.

• Inhibitory impact of subliminal electrical finger stimulation on SI representation and perceptual sensitivity of an adjacent finger.

  Authors: Birol Taskin, Susanne Holtze, Thomas Krause, Arno Villringer

  NeuroImage. 03/2008; 39(3):1307-13.

  Simultaneous stimulation of two adjacent fingers above sensory perception threshold (supraliminal stimulation) leads to an inhibitory interaction effect on responses in primary somatosensory cortexSimultaneous stimulation of two adjacent fingers above sensory perception threshold (supraliminal stimulation) leads to an inhibitory interaction effect on responses in primary somatosensory cortex (SI). Moreover, during electrical finger stimulation closely below threshold for conscious perception (subliminal stimulation) inhibitory interneurons in cortical layer 4 are assumed to be activated preferentially as compared to excitatory interneurons. Using fMRI in humans, here we show that interspersed subliminal electrical stimulation of an adjacent finger reduces the response to target finger stimulation in contralateral SI. This effect was shown in a complementary study to be associated behaviorally with a diminished detectability of test pulses on the target finger. We propose the mechanism underlying this lateral inhibitory effect to be related to a representational overlap of inhibitory interneurons in SI based on the divergence of thalamocortical feedforward projections, or to intracortical lateral inhibitory projections targeting juxtaposed receptive fields, or both.

• Inhibitory impact of subliminal electrical finger stimulation on SI representation and perceptual sensitivity of an adjacent finger

  Authors: Birol Taskin, Susanne Holtze, Thomas Krause, Amo Villringer

  NeuroImage. 39(3):1307-1313.

  Simultaneous stimulation of two adjacent fingers above sensory perception threshold (supraliminal stimulation) leads to an inhibitory interaction effect on responses in primary somatosensory cortexSimultaneous stimulation of two adjacent fingers above sensory perception threshold (supraliminal stimulation) leads to an inhibitory interaction effect on responses in primary somatosensory cortex (SI). Moreover, during electrical finger stimulation closely below threshold for conscious perception (subliminal stimulation) inhibitory interneurons in cortical layer 4 are assumed to be activated preferentially as compared to excitatory interneurons. Using fMRI in humans, here we show that interspersed subliminal electrical stimulation of an adjacent finger reduces the response to target finger stimulation in contralateral SI. This effect was shown in a complementary study to be associated behaviorally with a diminished detectability of test pulses on the target ringer. We propose the mechanism underlying this lateral inhibitory effect to be related to a representational overlap of inhibitory interneurons in SI based on the divergence of thalamocortical feedforward projections, or to intracortical lateral inhibitory projections targeting juxtaposed receptive fields, or both. (c) 2007 Elsevier Inc. All rights reserved.