Tibor Auer

Publications (20) View all

• Source

  Available from: Tibor Auer

  Article: An iterative two-threshold analysis for single-subject functional MRI of the human brain.

  Tibor Auer, Renate Schweizer, Jens Frahm
  [show abstract] [hide abstract]
  ABSTRACT: Current thresholding strategies for the analysis of functional MRI (fMRI) datasets may suffer from specific limitations (e.g. with respect to the required smoothness) or lead to reduced performance for a low signal-to-noise ratio (SNR). Although a previously proposed two-threshold (TT) method offers a promising solution to these problems, the use of preset settings limits its performance. This work presents an optimised TT approach that estimates the required parameters in an iterative manner. The iterative TT (iTT) method is compared with the original TT method, as well as other established voxel-based and cluster-based thresholding approaches and spatial mixture modelling (SMM) for both simulated data and fMRI of a hometown walking task at different experimental settings (spatial resolution, filtering and SNR). In general, the iTT method presents with remarkable sensitivity and good specificity that outperforms all conventional approaches tested except for SMM in a few cases. This also holds true for challenging conditions such as high spatial resolution, the absence of filtering, high noise level, or a low number of task repetitions. Thus, iTT emerges as a good candidate for both scientific fMRI studies at high spatial resolution and more routine applications for clinical purposes.
  European Radiology 06/2011; 21(11):2369-87. · 3.22 Impact Factor
• Source

  Available from: Hans Strasburger

  Article: Temporal frequency and chromatic processing in humans: an fMRI study of the cortical visual areas.

  Dany V D'Souza, Tibor Auer, Hans Strasburger, Jens Frahm, Barry B Lee
  [show abstract] [hide abstract]
  ABSTRACT: Psychophysical sensitivity to isoluminant chromatic modulation declines at temporal frequencies beyond 4 Hz, whereas chromatically opponent cells of the afferent visual pathway (long- to middle-wavelength (L-M) cone-opponent or short-wavelength (S) cone cells) show responses at much higher temporal frequencies, indicating a central limitation in temporal processing capacity. Here, we sought to localize this limit in cortical retinotopic visual areas. We used fMRI to investigate responses of lateral geniculate nucleus and cortical visual areas in humans to isoluminant chromatic modulation as a function of temporal frequency (2-12 Hz). Our results suggest that L-M cone-opponent and S-cone signals are processed in LGN up to 12 Hz. In all visual areas except MT (middle temporal) and V3a, S-cone responses declined steeply with temporal frequency, implying that psychophysical sensitivity loss to blue-yellow modulation might occur early within these areas. While V1 showed robust L-M responses up to 12 Hz, there was a progressive falloff of responses with temporal frequency as information is transferred from V1 to higher areas (V2, V3, and V4), suggesting that, in humans, temporal limitation in perception of red-green chromatic modulation likely results from limited processing capacity of higher ventral extrastriate areas.
  Journal of Vision 01/2011; 11(8). · 3.38 Impact Factor
• Source

  Available from: Tibor Auer

  Article: Confounding factors in neurofeedback training based on fMRI of motor imagery

  Tibor Auer, Jens Frahm
  [show abstract] [hide abstract]
  ABSTRACT: Introduction: The utility of fMRI-based neurofeedback has been demonstrated for the regulation of cortical activity in the primary sensorimotor (SM1) areas. However, differences between right and left-hand training as well as confounds such as age, gender, and handedness were not yet investigated. Methods: Sixteen young healthy adults underwent a fourweek-long fMRI-based neurofeedback of SM1 responsible for hand movement. Left and right SM1 were identified individually using a functional localizer task. The goal of the training was to increase the fMRI signal difference between the left and right SM1 presented back to the subjects in real time. Eleven demographically matched individuals without training served as controls. In both groups, the initial and terminal sessions included fMRI during motor imagery without feedback (baseline measurement). Training performance was defined as increase in the fMRI signal difference between the left and right SM1 that was achieved in pre- and post-training baseline measurements. Results: The training performance was significantly higher in the training group vs the control group (p = 0.001 for each hand). For the right hand, females (p = 0.028) and older subjects (p = 0.033) performed better. Whole-brain analysis revealed a significantly higher increase in activation of SM1 in the training group vs the control group for each hand. For right-hand training, increase in activation in the right SM1 (contralateral to the target ROI) and premotor area (Br6) was positively correlated with handedness, while increase in activation in the left SM1 (target ROI) and Br6 correlated with age. For left-hand training, recruitment showed a positive correlation with handedness in supplementary motor area and Br6 bilaterally. Conclusion: Individual training performance in fMRI-based neurofeedback employing motor imagery is affected by age and gender and – despite of a symmetrical setup – may be accompanied by lateralized functional changes depending on handedness. Acknowledgements: Financial support by the German Federal Ministry for Education and Research (BMBF) via the Bernstein Focus Neurotechnologie (BFNT) Göttingen (Grant no. 01GQ0812) is gratefully acknowledged.
  Neuroscience letters. Supplement 01/2011; 500(S):e32.
• Article: Attack-related brainstem activation in a patient with SUNCT syndrome: an ictal fMRI study.

  Tibor Auer, József Janszky, Attila Schwarcz, Tamás Dóczi, Anita Trauninger, Bálint Alkonyi, Sámuel Komoly, Zoltán Pfund
  [show abstract] [hide abstract]
  ABSTRACT: The authors report functional magnetic resonance imaging (fMRI) study data of a 60-year-old patient having short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) syndrome. Three consecutive pain attacks were detected during the imaging session and strong brainstem activation was found. It was concluded that the brainstem can be involved in the pain signal transmission in SUNCT syndrome.
  Headache The Journal of Head and Face Pain 03/2009; 49(6):909-12. · 2.52 Impact Factor
• Article: Does obstetric brachial plexus injury influence speech dominance?

  Tibor Auer, Sandor Pinter, Norbert Kovacs, Zsuzsanna Kalmar, Ferenc Nagy, Reka A Horvath, Balazs Koszo, Gyula Kotek, Gabor Perlaki, Maria Koves, Bernadette Kalman, Samuel Komoly, Attila Schwarcz, Friedrich G Woermann, Jozsef Janszky
  [show abstract] [hide abstract]
  ABSTRACT: Right-handedness and left-sided language lateralization is an unresolved mystery with unknown cause/effect relations. Most studies suggest that the language lateralization is related to a fundamental brain asymmetry: right-handedness may be secondary. We analyzed the possibility of an opposite cause/effect relation: whether asymmetric hand usage (as a cause) can influence language lateralization (as a consequence). We determined language lateralization by functional magnetic resonance imaging in 15 subjects whose upper limb (UL) had been injured at birth because of unilateral damage of the brachial plexus. These subjects were able to use only one (the noninjured) UL perfectly. We found correlation between the severity of right-sided UL injuries and hand usage dysfunction and the degree of left-to-right shift of language lateralization. There was, however, not a complete switch of language lateralization. Right-sided UL injury can induce a left-to-right shift in language lateralization, suggesting that hand usage can influence language lateralization. These findings may contradict the broadly accepted theory that right-handedness is a secondary phenomenon caused by left-sided hemispheric language lateralization. However, the cause/effect problem between asymmetric hand usage and language lateralization is not resolved in this study. Our findings may support the theory that gestures had a crucial role in human language evolution and is a part of the language system even today.
  Annals of Neurology 03/2009; 65(1):57-66. · 11.09 Impact Factor