title: Intensity changes in a continuous tone: auditory cortical potentials comparison with frequency changes.
abstract: OBJECTIVE
  To examine auditory cortical potentials in normal-hearing subjects to intensity increments in a continuous pure tone at low, mid, and high frequency.
  
  
  METHODS
  Electrical scalp potentials were recorded in response to randomly occurring 100 ms intensity increments of continuous 250, 1000, and 4000 Hz tones every 1.4 s. The magnitude of intensity change varied between 0, 2, 4, 6, and 8 dB above the 80 dB SPL continuous tone.
  
  
  RESULTS
  Potentials included N100, P200, and a slow negative (SN) wave. N100 latencies were delayed whereas amplitudes were not affected for 250 Hz compared to 1000 and 4000 Hz. Functions relating the magnitude of the intensity change and N100 latency/amplitude did not differ in their slope among the three frequencies. No consistent relationship between intensity increment and SN was observed. Cortical dipole sources for N100 did not differ in location or orientation between the three frequencies.
  
  
  CONCLUSIONS
  The relationship between intensity increments and N100 latency/amplitude did not differ between tonal frequencies. A cortical tonotopic arrangement was not observed for intensity increments. Our results are in contrast to prior studies of brain activities to brief frequency changes showing cortical tonotopic organization.
  
  
  CONCLUSIONS
  These results suggest that intensity and frequency discrimination employ distinct central processes.
authors.affiliation: Department of Neurology, University of California, 150 Med Surge 1, Irvine, CA 92697, USA. adimitri@uci.edu
authors.forename: Andrew
authors.initials: A
authors.lastname: Dimitrijevic
authors.forename: Brenda
authors.initials: B
authors.lastname: Lolli
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Michalewski
authors.forename: Hillel
authors.initials: H
authors.lastname: Pratt
authors.forename: Fan-Gang
authors.initials: FG
authors.lastname: Zeng
authors.forename: Arnold
authors.initials: A
authors.lastname: Starr
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000704:Analysis of Variance; D001303:Auditory Cortex / Q000033:anatomy & histology / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D001931:Brain Mapping; D004569:Electroencephalography / Q000379:methods; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D011571:Psychoacoustics; D011930:Reaction Time / Q000502:physiology; D013057:Spectrum Analysis; D055815:Young Adult