Identifying auditory cortex encoding abnormalities in schizophrenia: The utility of low-frequency versus 40 Hz steady-state measures

Abstract

Magnetoencephalography (MEG) and EEG have identified poststimulus low frequency and 40 Hz steady-state auditory encoding abnormalities in schizophrenia (SZ). Negative findings have also appeared. To identify factors contributing to these inconsistencies, healthy control (HC) and SZ group differences were examined in MEG and EEG source space and EEG sensor space, with better group differentiation hypothesized for source than sensor measures given greater predictive utility for source measures. Fifty-five HC and 41 chronic SZ were presented 500 Hz sinusoidal stimuli modulated at 40 Hz during simultaneous whole-head MEG and EEG. MEG and EEG source models using left and right superior temporal gyrus (STG) dipoles estimated trial-to-trial phase similarity and percent change from prestimulus baseline. Group differences in poststimulus low-frequency activity and 40 Hz steady-state response were evaluated. Several EEG sensor analysis strategies were also examined. Poststimulus low-frequency group differences were observed across all methods. Given an age-related decrease in left STG 40 Hz steady-state activity in HC (HC > SZ), 40 Hz steady-state group differences were evident only in younger participants' source measures. Findings thus indicated that optimal data collection and analysis methods depend on the auditory encoding measure of interest. In addition, whereas results indicated that HC and SZ auditory encoding low-frequency group differences are generally comparable across modality and analysis strategy (and thus not dependent on obtaining construct-valid measures of left and right auditory cortex activity), 40 Hz steady-state group-difference findings are much more dependent on analysis strategy, with 40 Hz steady-state source-space findings providing the best group differentiation.

Keywords: auditory encoding; electroencephalography; magnetoencephalography; schizophrenia; superior temporal gyrus.

Figure 1

Total power and inter-trial coherence time-frequency plots (grand average of controls shown), with boxplots (MEG = green border; EEG = yellow border) showing the mean and 95% confidence intervals for each group (HC = blue; SZ = red) for left and right STG post-stimulus low-frequency activity (4 to 16Hz activity averaged from 50 to 200 ms) and 40Hz steady-state activity (38 to 42Hz activity averaged from 500 to 1000 ms). In the boxplots, significant group differences are indicated (*p<0.05; **p<0.001; trends below p = 0.10 reported with p-value).

Figure 2

Scatterplots showing correlations between age and left and right STG 40Hz steady-state activity for MEG (left panels) and EEG (right panels), and for total power (TP, upper row) and inter-trial coherence (ITC, lower row). HC shown in blue and SZ in red. R² values show the percent variance explained.

Figure 3

The same as Figure 1 but showing findings for the younger and older participants. In the boxplots, significant pairwise group differences are indicated (*p<0.05; **p<0.001; trends below p = 0.10 reported with p-value).