title: The neurochemical basis of human cortical auditory processing: combining proton magnetic resonance spectroscopy and magnetoencephalography.
abstract: BACKGROUND
  A combination of magnetoencephalography and proton magnetic resonance spectroscopy was used to correlate the electrophysiology of rapid auditory processing and the neurochemistry of the auditory cortex in 15 healthy adults. To assess rapid auditory processing in the left auditory cortex, the amplitude and decrement of the N1m peak, the major component of the late auditory evoked response, were measured during rapidly successive presentation of acoustic stimuli. We tested the hypothesis that: (i) the amplitude of the N1m response and (ii) its decrement during rapid stimulation are associated with the cortical neurochemistry as determined by proton magnetic resonance spectroscopy.
  
  
  RESULTS
  Our results demonstrated a significant association between the concentrations of N-acetylaspartate, a marker of neuronal integrity, and the amplitudes of individual N1m responses. In addition, the concentrations of choline-containing compounds, representing the functional integrity of membranes, were significantly associated with N1m amplitudes. No significant association was found between the concentrations of the glutamate/glutamine pool and the amplitudes of the first N1m. No significant associations were seen between the decrement of the N1m (the relative amplitude of the second N1m peak) and the concentrations of N-acetylaspartate, choline-containing compounds, or the glutamate/glutamine pool. However, there was a trend for higher glutamate/glutamine concentrations in individuals with higher relative N1m amplitude.
  
  
  CONCLUSIONS
  These results suggest that neuronal and membrane functions are important for rapid auditory processing. This investigation provides a first link between the electrophysiology, as recorded by magnetoencephalography, and the neurochemistry, as assessed by proton magnetic resonance spectroscopy, of the auditory cortex.
authors.affiliation: Department of Imaging Research, Sunnybrook Health Sciences Centre, Toronto, ON, Canada. peter.soros@sri.utoronto.ca
authors.forename: Peter
authors.initials: P
authors.lastname: Sörös
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Michael
authors.forename: Melanie
authors.initials: M
authors.lastname: Tollkötter
authors.forename: Bettina
authors.initials: B
authors.lastname: Pfleiderer
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D001303:Auditory Cortex / Q000378:metabolism / Q000502:physiology*; D002794:Choline / Q000378:metabolism; D005072:Evoked Potentials, Auditory; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged
chemical_list: D005973:Glutamine; D001224:Aspartic Acid; D018698:Glutamic Acid; C000179:N-acetylaspartate; D002794:Choline