title: Diurnal stability of gamma-aminobutyric acid concentration in visual and sensorimotor cortex.
abstract: OBJECTIVE
  To establish the diurnal stability of edited magnetic resonance spectroscopy measurements of gamma-aminobutyric acid (GABA) in visual and sensorimotor regions of the brain.
  
  
  METHODS
  GABA measurements were made in two regions of the brain (an occipital, "visual" region and a "sensorimotor" region centered on the precentral gyrus) using the MEGA-PRESS editing method, scanning eight healthy adults at five timepoints during a single day. GABA concentration was quantified from the ratio of the GABA integral to the unsuppressed water signal.
  
  
  RESULTS
  No significant effect of time on GABA concentration was seen (P = 0.35). GABA was shown to be significantly more concentrated in visual regions than in sensorimotor regions (1.10 i.u. and 1.03 i.u., respectively; P = 0.050). Coefficients of variability (CVs) across all subjects of 9.1% and 12% (visual and sensorimotor) were significantly higher than mean within-subjects CVs of 6.5% and 8.8.
  
  
  CONCLUSIONS
  This study demonstrates the excellent reproducibility of MEGA-PRESS detection of GABA, demonstrating that the method is sufficiently sensitive to detect inter-subject variability, and suggests that (within the sensitivity limits of current measurements) time of day can be ignored in the design of MRS studies of visual and sensorimotor regions.
authors.affiliation: CUBRIC, School of Psychology, Cardiff University, Cardiff, Wales, UK.
authors.forename: Christopher John
authors.initials: CJ
authors.lastname: Evans
authors.forename: David John
authors.initials: DJ
authors.lastname: McGonigle
authors.forename: Richard Anthony Edward
authors.initials: RA
authors.lastname: Edden
mesh_terms: D002648:Child; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D009044:Motor Cortex / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013003:Somatosensory Cortex / Q000378:metabolism*; D014793:Visual Cortex / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000032:analysis*
chemical_list: D005680:gamma-Aminobutyric Acid