title: Magnetoencephalographic evidence of abnormal auditory processing in amyotrophic lateral sclerosis with bulbar signs.
abstract: OBJECTIVE
  Amyotrophic lateral sclerosis (ALS) is characterized by progressive motor neuron damage that gives rise to muscle denervation. Besides motor neuron damage, conscious auditory processing appears to be impaired in ALS, whereas it has remained ambiguous whether preceding automatic auditory processing is abnormal in ALS and specifically in ALS with bulbar signs.
  
  
  METHODS
  Auditory evoked fields (AEFs) to monaurally presented frequent and infrequent tones with stimulus intervals of 500 and 2500 ms were recorded with magnetoencephalography (MEG) from 10 ALS patients having bulbar signs and from 10 age-matched healthy subjects.
  
  
  RESULTS
  The amplitudes of the P50m and N100m responses, which index automatic auditory processing underlying stimulus detection, were significantly increased and P50m latency was shortened in ALS patients. MMNm, which reflects memory-based auditory comparison process, was increased in amplitude in the patient group, whereas the MMNm latency was similar in both groups. AEF latency and amplitude values failed to correlate with the severity of ALS as measured by ALS Functional Rating Scale (ALSFRS).
  
  
  CONCLUSIONS
  The present results suggest that auditory processing underlying stimulus detection, and subsequent memory-based comparison processes are abnormal in ALS patients with severe bulbar signs. This might be due to cortical overactivity of excitatory neurotransmitter glutamate observed in ALS.
authors.affiliation: Department of Neurology, Helsinki University Central Hospital, Helsinki, Finland. eero.pekkonen@hus.fi
authors.forename: Eero
authors.initials: E
authors.lastname: Pekkonen
authors.forename: Daria
authors.initials: D
authors.lastname: Osipova
authors.forename: Hannu
authors.initials: H
authors.lastname: Laaksovirta
mesh_terms: D000161:Acoustic Stimulation; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000150:complications / Q000503:physiopathology*; D000704:Analysis of Variance; D001308:Auditory Perceptual Disorders / Q000150:complications / Q000503:physiopathology*; D016022:Case-Control Studies; D004569:Electroencephalography / Q000379:methods; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005260:Female; D007839:Functional Laterality; D006257:Head / Q000503:physiopathology; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D011930:Reaction Time