Measurement of brain lactate during visual stimulation using a long TE semi‐LASER sequence at 7 T

Abstract

Estimation of metabolic changes during neuronal activation represents a challenge for in vivo MRS, especially for metabolites with low concentration and signal overlap, such as lactate. In this work, we aimed to evaluate the feasibility of detecting lactate during brain activation using a long TE (144 ms) semi‐LASER sequence at 7 T. 1normalH spectra were acquired on healthy volunteers ( N=6) during a paradigm with 15 min of visual stimulation. Outer‐volume signals were further attenuated by the use of saturation slabs, and macromolecular signals in the vicinity of the inverted lactate peak were individually fitted with simulated Lorentzian peaks. All spectra were free of artefacts and highly reproducible across subjects. Lactate was accurately quantified with an average Cramér‐Rao lower bound of 8%. Statistically significant ( P<0.05, one‐tailed t‐test) increases in lactate ( ∼10%) and glutamate ( ∼3%) levels during stimulation were detected in the visual cortex. Lactate and glutamate changes were consistent with previous measurements. We demonstrated that quantification of a clear and non‐contaminated lactate peak obtained with a long TE sequence has the potential of improving the accuracy of functional MRS studies targeting non‐oxidative reaction pathways.

Simultaneous detection of metabolite concentration changes, water BOLD signal and pH changes during visual stimulation in the human brain at 9.4T

“…4,5 Also, more recent studies use J-edited and long TE methods to look specifically at lactate, c-aminobutyric acid (GABA), and glutamate and glutamine (Glx) alterations under visual stimulation. [6][7][8] While editing and long TE sequences intrinsically remove overlapping signals, therefore enabling precise assessment of changes in Lac, GABA, and Glx, short TE non-edited measurements are advantageous because of high SNR and the simultaneous detection of a wide range of brain metabolites. Several short TE non-edited 1 H fMRS studies have previously been performed in the human brain under visual stimulation at an ultra-high field (UHF) strength of 7 T. [8][9][10][11][12][13][14][15][16][17] They consistently report increases of lactate (Lac) and glutamate (Glu) during stimulation.…”

Perception is associated with the brain’s metabolic response to sensory stimulation

“…The metabolic response to stimulation includes an oxidative component, as measured by the cerebral metabolic rate of oxygen (CMRO 2 ), and a nonoxidative component, as reflected by lactate accumulation ( Mangia et al, 2009 ). Cortical lactate levels have been shown to increase during visual stimulation, simultaneously to the acceleration of the malate–aspartate shuttle (MAS), a process termed aerobic glycolysis (i.e., lactate production independent of oxygen availability) ( Bednařík et al, 2015 ; Bednařík et al, 2018 ; Boillat et al, 2020 ; Fernandes et al, 2020 ; Lin et al, 2010 ; Lin et al, 2012 ; Mangia et al, 2007a ; Schaller et al, 2013 ; Schaller et al, 2014 ). Despite intense research, the neurophysiological mechanisms underlying the upregulation of glycolytic metabolism of glucose are still largely unknown ( Dienel, 2019a ).…”

Perception affects the brain’s metabolic response to sensory stimulation

“…Cortical lactate levels have been shown to increase during visual stimulation, simultaneously to the acceleration of the malate-aspartate shuttle, a process termed aerobic glycolysis (i.e. lactate production independent of oxygen availability) (3)(4)(5)(6)(7)(8)(9)(10)(11). Despite intense research, the neurophysiological mechanisms underlying the up-regulation of glycolytic metabolism of glucose are still largely unknown (12).…”