Auditory-Evoked Potentials to Frequency Increase and Decrease

Objective

To define cortical brain responses to large and small frequency changes (increase and decrease) of high- and low-frequency tones.

Methods

Event-Related Potentials (ERPs) were recorded in response to a 10% or a 50% frequency increase from 250 or 4000Hz tones that were approximately 3s in duration and presented at 500-ms intervals. Frequency increase was followed after 1s by a decrease back to base frequency. Frequency changes occurred at least 1s before or after tone onset or offset, respectively. Subjects were not attending to the stimuli. Latency, amplitude and source current density estimates of ERPs were compared across frequency changes.

Results

All frequency changes evoked components P50, N100, and P200. N100 and P200 had double peaks at bilateral and right temporal sites, respectively. These components were followed by a slow negativity (SN). The constituents of N100 were predominantly localized to temporo-parietal auditory areas. The potentials and their intracranial distributions were affected by both base frequency (larger potentials to low frequency) and direction of change (larger potentials to increase than decrease), as well as by change magnitude (larger potentials to larger change). The differences between frequency increase and decrease depended on base frequency (smaller difference to high frequency) and were localized to frontal areas.

Conclusions

Brain activity varies according to frequency change direction and magnitude as well as base frequency.

Significance

The effects of base frequency and direction of change may reflect brain networks involved in more complex processing such as speech that are differentially sensitive to frequency modulations of high (consonant discrimination) and low (vowels and prosody) frequencies.

Keywords: event-related potentials, spectral change, frequency resolution, change complex, source estimation, functional imaging

Pratt, H., Starr, A., Michalewski, H. J., Dimitrijevic, A., Bleich, N., & Mittelman, N. (2009). Auditory-evoked potentials to frequency increase and decrease of high- and low-frequency tones. Clinical Neurophysiology, 120(2), 360-373. doi:10.1016/j.clinph.2008.10.158