@article{GramAlbertovaSchirmeretal.2022,
  author    = {Gram, Maximilian and Albertova, P. and Schirmer, V. and Blaimer, M. and Gamer, M. and Herrmann, M. J. and Nordbeck, P. and Jakob, P. M.},
  title     = {Towards robust in vivo quantification of oscillating biomagnetic fields using Rotary Excitation based MRI},
  series = {Scientific Reports},
  volume    = {12},
  journal   = {Scientific Reports},
  number    = {1},
  doi       = {10.1038/s41598-022-19275-5},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300862},
  year      = {2022},
  abstract  = {Spin-lock based functional magnetic resonance imaging (fMRI) has the potential for direct spatially-resolved detection of neuronal activity and thus may represent an important step for basic research in neuroscience. In this work, the corresponding fundamental effect of Rotary EXcitation (REX) is investigated both in simulations as well as in phantom and in vivo experiments. An empirical law for predicting optimal spin-lock pulse durations for maximum magnetic field sensitivity was found. Experimental conditions were established that allow robust detection of ultra-weak magnetic field oscillations with simultaneous compensation of static field inhomogeneities. Furthermore, this work presents a novel concept for the emulation of brain activity utilizing the built-in MRI gradient system, which allows REX sequences to be validated in vivo under controlled and reproducible conditions. Via transmission of Rotary EXcitation (tREX), we successfully detected magnetic field oscillations in the lower nano-Tesla range in brain tissue. Moreover, tREX paves the way for the quantification of biomagnetic fields.},
  language  = {en}
}
@article{VernerHerrmannTrocheetal.2013,
  author    = {Verner, Martin and Herrmann, Martin J. and Troche, Stefan J. and Roebers, Claudia M. and Rammsayer, Thomas H.},
  title     = {Cortical oxygen consumption in mental arithmetic as a function of task difficulty: a near-infrared spectroscopy approach},
  series = {Frontiers in Human Neuroscience},
  volume    = {7},
  journal   = {Frontiers in Human Neuroscience},
  number    = {217},
  issn      = {1662-5161},
  doi       = {10.3389/fnhum.2013.00217},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-122449},
  year      = {2013},
  abstract  = {The present study investigated changes in cortical oxygenation during mental arithmetic using near-infrared spectroscopy (NIRS). Twenty-nine male volunteers were examined using a 52-channel continuous wave system for analyzing activity in prefrontal areas. With the help of a probabilistic mapping method, three regions of interest (ROIs) on each hemisphere were defined: The inferior frontal gyri (IFG), the middle frontal gyri (MFG), and the superior frontal gyri (SFG). Oxygenation as an indicator of functional brain activation was compared over the three ROI and two levels of arithmetic task difficulty (simple and complex additions). In contrast to most previous studies using fMRI or NIRS, in the present study arithmetic tasks were presented verbally in analogue to many daily life situations. With respect to task difficulty, more complex addition tasks led to higher oxygenation in all defined ROI except in the left IFG compared to simple addition tasks. When compared to the channel positions covering different gyri of the temporal lobe, the observed sensitivity to task complexity was found to be restricted to the specified ROIs. As to the comparison of ROIs, the highest oxygenation was found in the IFG, while MFG and SFG showed significantly less activation compared to IFG. The present cognitive-neuroscience approach demonstrated that NIRS is a suitable and highly feasible research tool for investigating and quantifying neural effects of increasing arithmetic task difficulty.},
  language  = {en}
}
@article{KatzorkeZellerMuelleretal.2017,
  author    = {Katzorke, Andrea and Zeller, Julia B. M. and M{\"u}ller, Laura D. and Lauer, Martin and Polak, Thomas and Reif, Andreas and Deckert, J{\"u}rgen and Herrmann, Martin J.},
  title     = {Reduced activity in the right inferior frontal gyrus in elderly APOE-E4 carriers during a verbal fluency task},
  series = {Frontiers in Human Neuroscience},
  volume    = {11},
  journal   = {Frontiers in Human Neuroscience},
  doi       = {10.3389/fnhum.2017.00046},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171892},
  year      = {2017},
  abstract  = {Apolipoprotein-E4 (APOE-E4) is a major genetic risk factor for developing Alzheimer's disease (AD). The verbal fluency task (VFT), especially the subtask category fluency, has shown to provide a good discrimination between cognitively normal controls and subjects with AD. Interestingly, APOE-E4 seems to have no effect on the behavioral performance during a VFT in healthy elderly. Thus, the purpose of the present study was to reveal possible compensation mechanisms by investigating the effect of APOE-E4 on the hemodynamic response in non-demented elderly during a VFT by using functional near-infrared spectroscopy (fNIRS). We compared performance and hemodynamic response of high risk APOE-E4/E4, -E3/E4 carriers with neutral APOE-E3/E3 non-demented subjects (N = 288; 70-77 years). No difference in performance was found. APOE-E4/E4, -E3/E4 carriers had a decreased hemodynamic response in the right inferior frontal junction (IFJ) with a corresponding higher response in the left middle frontal gyrus (MFG) during category fluency. Performance was correlated with the hemodynamic response in the MFG. We assume a compensation of decreased IFJ brain activation by utilizing the MFG during category fluency and thus resulting in no behavioral differences between APOE-groups during the performance of a VFT.},
  language  = {en}
}
@article{NeufangAkhrifHerrmannetal.2016,
  author    = {Neufang, S. and Akhrif, A. and Herrmann, C.G. and Drepper, C. and Homola, G.A. and Nowak, J. and Waider, J. and Schmitt, A.G. and Lesch, K.-P. and Romanos, M.},
  title     = {Serotonergic modulation of 'waiting impulsivity' is mediated by the impulsivity phenotype in humans},
  series = {Translational Psychiatry},
  journal   = {Translational Psychiatry},
  number    = {6},
  doi       = {10.1038/tp.2016.210},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164418},
  pages     = {e940},
  year      = {2016},
  abstract  = {In rodents, the five-choice serial reaction time task (5-CSRTT) has been established as a reliable measure of waiting impulsivity being defined as the ability to regulate a response in anticipation of reinforcement. Key brain structures are the nucleus accumbens (NAcc) and prefrontal regions (for example, pre- and infralimbic cortex), which are, together with other transmitters, modulated by serotonin. In this functional magnetic resonance imaging study, we examined 103 healthy males while performing the 5-CSRTT measuring brain activation in humans by means of a paradigm that has been widely applied in rodents. Subjects were genotyped for the tryptophan hydroxylase-2 (TPH2; G-703T; rs4570625) variant, an enzyme specific for brain serotonin synthesis. We addressed neural activation patterns of waiting impulsivity and the interaction between the NAcc and the ventromedial prefrontal cortex (vmPFC) using dynamic causal modeling. Genetic influence was examined via interaction analyses between the TPH2 genotype (GG homozygotes vs T allele carriers) and the degree of impulsivity as measured by the 5-CSRTT. We found that the driving input of the vmPFC was reduced in highly impulsive T allele carriers (reflecting a reduced top-down control) in combination with an enhanced response in the NAcc after correct target processing (reflecting an augmented response to monetary reward). Taken together, we found a high overlap of our findings with reports from animal studies in regard to the underlying cognitive processes, the brain regions associated with waiting impulsivity and the neural interplay between the NAcc and vmPFC. Therefore, we conclude that the 5-CSRTT is a promising tool for translational studies.},
  language  = {en}
}