Efference copy/corollary discharge function and targeted cognitive training in patients with schizophrenia

Abstract

Introduction: During vocalization, efference copy/corollary discharge mechanisms suppress the auditory cortical response to self-generated sounds as reflected in the N1 component of the auditory event-related potential (ERP). N1 suppression during talking is reduced in patients with schizophrenia. We hypothesized that these deficits would recover with auditory training that targets the speech processing system.

Methods: Forty-nine individuals early in the course of a schizophrenia-spectrum illness (ESZ) were randomly assigned to 40 h of Targeted Auditory Training (TAT; n = 23) or Computer Games (CG; n = 26). The N1 ERP component was elicited during production (Talk) and playback (Listen) of vocalization. Effects of Treatment on Global Cognition, N1 suppression (Talk-Listen), N1 during Talking and Listening were assessed. Simple effects of the passage of time were also assessed in the HC after 28 weeks.

Results: There was a Treatment × Time interaction revealing that N1 suppression was improved with TAT, but not with CG. TAT, but not CG, also improved Global Cognition. However, TAT and CG groups differed in their pre-treatment N1 suppression, and greater N1-suppression abnormalities were strongly associated with greater improvement in N1 suppression.

Conclusions: In this sample of ESZ individuals, targeted auditory training appeared to improve the function of the efference copy/corollary discharge mechanism which tended to deteriorate with computer games. It remains to be determined if baseline N1 suppression abnormalities are necessary for TAT treatment to have a positive effect on efference copy/corollary discharge function or if improvements observed in this study represent a regression to the mean N1 suppression in ESZ.

Trial registration: ClinicalTrials.govNCT00694889. Registered 1 August 2007.

Keywords: Auditory ERP; Cognitive training; Efference copy/corollary discharge; Schizophrenia.

Figure 1.

ERP waveforms for Talk and Listen conditions show the N1 component during the Talk (grey) and Listen (black) conditions recorded at Cz. The N1 amplitude during Talk is reduced relative to Listen in Healthy Controls (HC, top). This effect is attenuated in the Early Schizophrenia Patients who were enrolled in either Targeted Auditory Training (TAT, bottom) or an active Computer Games control condition (CG, middle). Waveforms on the left-hand side show Time 1 (pre-treatment) data, while Time 2 (post-treatment for patients and approximately 6 months following Time 1 for HC) are plotted on the right-hand side.

Figure 2.

Line graphs show the electrode Cz mean N1 Talk (left), N1 Listen (middle), and N1 Suppresison (Talk-Listen difference, right) z-scores pre- (Time 1) and post-treatment (Time 2) for the Targeted Auditory Training (TAT) and active Computer Games control (CG) treatment groups. The z-scores are based on age-correction done using a healthy control (HC) group, such that the 0 is the expected mean value for the HC group, controlling for age. Negative Talk z-scores reflect larger (i.e., more negative) N1 amplitude, positive Listen z-scores reflect smaller (i.e., less negative) N1 amplitude, and negative Talk-Listen suppression z-scores reflect reduced suppression.