Intensity changes in a continuous tone: auditory cortical potentials comparison with frequency changes.
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.
Dimitrijevic
Andrew
A
Department of Neurology, University of California, 150 Med Surge 1, Irvine, CA 92697, USA. adimitri@uci.edu
Lolli
Brenda
B
Michalewski
Henry J
HJ
Pratt
Hillel
H
Zeng
Fan-Gang
FG
Starr
Arnold
A
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