title: Detection of metabolite changes in response to a varying visual stimulation paradigm using short-TE1H MRS at 7 T.
abstract: The two-fold benefit of1H magnetic resonance spectroscopy (MRS) at high B0fields - enhanced sensitivity and increased spectral dispersion - has been used previously to study dynamic changes in metabolite concentrations in the human brain in response to visual stimulation. In these studies, a strong visual on/off stimulus was combined with MRS data acquisition in a voxel location in the occipital cortex determined by an initial functional magnetic resonance imaging experiment. However, 1) to exclude the possibility of systemic effects (heartbeat, blood flow, etc.), which tend to be different for on/off conditions, a modified stimulation condition not affecting the target voxel needs to be employed, and 2) to assess important neurotransmitters of low concentration, in particular γ-aminobutyric acid (GABA), it may be advantageous to analyze steady-state, rather than dynamic, conditions. Thus, the aim of this study was to use short-TE1H MRS methodology at 7 T to detect differences in steady-state metabolite levels in response to a varying stimulation paradigm in the human visual cortex. The two different stimulation conditions were termed voxel and control activation. Localized MR spectra were acquired using the SPECIAL (spin-echo full-intensity acquired localized) sequence. Data were analyzed using LCModel. Fifteen individual metabolites were reliably quantified. On comparison of steady-state concentrations for voxel versus control activation, a decrease in GABA of 0.05 mmol/L (5%) and an increase in lactate of 0.04 mmol/L (7%) were found to be the only significant effects. The observed reduction in GABA can be interpreted as reduced neuronal inhibition during voxel activation, whereas the increase in lactate hints at an intensification of anaerobic glycolysis. Differences from previous studies, notably the absence of any changes in glutamate, are attributed to the modified experimental conditions. This study demonstrates that the use of advanced1H MRS methodology at 7 T allows the detection of subtle changes in metabolite concentrations involved in neuronal activation and inhibition.
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, and Berlin, Germany.|Center for Stroke Research Berlin (CSB), Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Mekle
authors.affiliation: Center for Lifespan Psychology, Max Planck Institute for Human Development, Berlin, Germany.|University Clinic Hamburg-Eppendorf, Clinic and Polyclinic for Psychiatry and Psychotherapy, Hamburg, Germany.
authors.forename: Simone
authors.initials: S
authors.lastname: Kühn
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, and Berlin, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Pfeiffer
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, and Berlin, Germany.
authors.forename: Semiha
authors.initials: S
authors.lastname: Aydin
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, and Berlin, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Schubert
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, and Berlin, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Ittermann
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism*; D005260:Female; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D057054:Molecular Imaging / Q000379:methods; D010775:Photic Stimulation / Q000379:methods*; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014018:Tissue Distribution; D014793:Visual Cortex / Q000378:metabolism*; D014796:Visual Perception / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D019344:Lactic Acid; D005680:gamma-Aminobutyric Acid
keywords: functional magnetic resonance spectroscopy; high magnetic field; human brain; short echo time; varying stimulation paradigm