Cortical high-gamma responses in auditory processing

Abstract

Purpose: This tutorial provides an introduction to cortical auditory spectral responses, focusing on event-related activity in the high-gamma frequencies (60-150 Hz), their recent emergence in neuroscience research, and potential clinical applications.

Method: Auditory high-gamma responses are described and compared with traditional cortical evoked responses, including the auditory evoked N1 response. Methods for acquiring and analyzing spectral responses, including time-frequency analyses, are discussed and contrasted with more familiar time-domain averaging approaches. Four cases are presented illustrating high-gamma response patterns associated with normal and impaired auditory processing.

Conclusions: Cortical auditory high-gamma responses may provide a useful clinical measure of auditory processing.

Figure 1

Single-channel normal electroencephalogram recordings showing the five major frequencies: delta, theta, alpha, beta, and gamma. Time (in seconds) is on the horizontal axis; amplitude (in decibels) is on the vertical axis.

Figure 2

Auditory high-gamma responses recorded with four different auditory stimuli from the same electrode site in a patient with normal auditory processing abilities (Case 1). Stimulus conditions are (A) tones (1200 Hz); (B) speech (/da/); (C) 40-Hz amplitude-modulated tone (carrier frequency = 1000 Hz); and (D) white noise. In (C), an auditory steady-state response is also visible at the tone amplitude modulation rate (40 Hz). Time is on the horizontal axis in seconds (0–0.4 s). Frequency is on the vertical axis in hertz (0–150 Hz). Statistically significant changes are color-coded, with red representing the largest increase in power (dB) from the prestimulus baseline, shown in blue.

Figure 3

Auditory high-gamma responses recorded with the syllable /da/ from the same electrode in a patient with normal auditory processing abilities (Case 1) using (A) a passive oddball paradigm and (B) an active oddball paradigm. Time is on the horizontal axis in seconds (0–0.2 s). Frequency is on the vertical axis in hertz (0–150 Hz). Statistically significant changes are color-coded, with red representing the largest increase in power (dB) from the prestimulus baseline, shown in blue.

Figure 4

Auditory high-gamma responses recorded from a patient with impaired auditory processing abilities (Case 2). Responses were elicited with (A) tones (1200 Hz) and (B) speech (/da/). Time is on the horizontal axis in seconds (0–0.3 s). Frequency is on the vertical axis in hertz (0–150 Hz). Statistically significant changes are color-coded, with red representing the largest increase in power (dB) from the prestimulus baseline, shown in blue.

Figure 5

Intracranial recording results from two patients with implanted left hemisphere electrodes. Electrode locations have been coregistered with each patient’s three-dimensional magnetic resonance imaging brain reconstructions; the lateral left view is shown. (A) Results from a patient with normal auditory processing abilities (Case 3). Top inset box shows evoked tone N1 response (waveform has been smoothed for display); middle inset box shows high-gamma response to same tone; bottom inset box shows high-gamma response to speech. (B) Results from a patient with auditory processing difficulties (Case 4). Evoked N1 response is shown in the top inset box (waveform has been smoothed for display); high-gamma response to tones is shown in the bottom inset box. Auditory speech recordings were not performed with the second patient.