Edited by: Qinghua He, Southwest University, China
Reviewed by: Deana Davalos, Colorado State University, USA; Jin Li, Chinese Academy of Sciences, China
*Correspondence: Yansong Li
This article was submitted to Psychopathology, a section of the journal Frontiers in Psychology
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A recent electrophysiological study suggests existing compensatory brain activity as a mechanism for functional recovery of visual attention detection (the capacity for detecting external cues) in symptomatically remitted schizophrenia patients. Despite such evidence, little is known about other aspects of attentional-related processes in schizophrenia during clinical remission, such as their capacity to concentrate on the task at hands without being interfered by distracting information. To this end, we recorded event-related brain potentials (ERPs) from 20 symptomatically remitted schizophrenia patients and 20 healthy controls while they engaged in a classic Stroop task. Symptomatically remitted patients showed comparable Stroop interference to healthy controls, indicating a degree of functional recovery of such a capacity in these patients. On the neural level, the N450 over the fronto-central and central regions, a component of the ERPs related to conflict detection, was found across both groups, although patients presented a reduced N450 relative to healthy controls. By contrast, the amplitude of the sustained potential (SP) (600–800 ms) over the parieto-central and parietal regions, a component of the ERPs related to conflict resolution, was significantly increased in patients relative to healthy controls. Furthermore, such increased SP amplitude correlated positively with improved behavioral accuracy in symptomatically remitted patients with schizophrenia. These findings reveal that symptomatically remitted patients with schizophrenia increasingly recruited the parietal activity involving successful conflict resolution to offset reduced conflict detection. Therefore, this provides further insight into compensatory mechanisms potentially involving a degree of functional recovery of attentional-related processes in schizophrenia during clinical remission.
Schizophrenia patients are characterized by a range of cognitive deficits (Elvevag and Goldberg,
Interference control is considered to be an important aspect of attentional-related processes, which is typically defined as cognitive processes enabling individuals to concentrate on the task at hands without being interfered by distracting information (Burgess and Braver,
Particularly, interference control impairments in schizophrenia patients have attracted growing research attention over the past decade. Earlier behavioral studies have found that patients with schizophrenia generally showed more Stroop interference effect than healthy controls (Hepp et al.,
Despite such evidence, little is still known about such a capacity in symptomatically remitted patients with schizophrenia, although previous studies have revealed existing neuropsychological deficits in some cognitive functions including theory of mind (Herold et al.,
The procedure of recruiting participants was based on our prior study (Chen et al.,
Age (years) | 23.25 ± 0.46 | 24.45 ± 0.87 | |
Education (years) | 12.20 ± 0.67 | 13.35 ± 0.48 | |
IQ | 91.80 ± 2.62 | 97.70 ± 2.54 | |
Duration of illness (months) | 33.55 ± 3.78 | ||
Medication |
234.95 ± 29.82 | ||
PANSS |
|||
Positive symptoms | 8.70 ± 0.42 | ||
Negative symptoms | 13.20 ± 0.83 | ||
General psychopathology | 25.45 ± 1.05 | ||
Total | 47.35 ± 1.49 |
We also recruited 20 healthy controls reporting no prior history of psychiatric illness and drug abuse. Healthy controls also underwent psychiatric evaluation. Both groups were matched in age, gender and education (Table
This study was implemented in accordance with the recommendations of the guidelines approved by the ethics committee of military general hospital of PLA. All subjects gave written informed consent in accordance with the Declaration of Helsinki. The protocol was approved by the ethics committee of military general hospital of PLA.
In the present study, we used the classic Stroop task. The stimuli were similar to that described in a previous study (Qiu et al.,
Stimuli were presented using the E-prime software 2.0 (Psychology Software Tools, Inc.). Each trial began with a fixation cross “+” for 200 ms in the center of the screen, followed by a blank screen lasting randomly from 800 to 1,200 ms. After the black screen, a stimulus was presented for 150 ms, followed by a blank screen until a response was made. If there was no response within 2,000 ms, this trial was coded as incorrect and the next trial would start (Figure
Participants were seated in a dimly light room facing a computer monitor placed at 80 cm distance from their eyes. They were required to put their right middle, right index, left index, and left middle finger on the appropriate color button on a game pad. They were told that a white fixation cross would always be presented first in the center of the screen, followed by a word written in each of four colors. They were required to respond to the color in which the stimuli were written by pressing the corresponding color-coded button on the game pad as fast and accurately as possible.
EEG was recorded (SynAmps amplifier, NeuroScan) with a quick cap carrying 32 Ag/AgCl electrodes (Fp1, Fp2, F3, Fz, F4, Fc3, Fcz, Fc4, C3, Cz, C4, CP3, CPz, CP4, P3, Pz, P4, F7, F8, Ft7, Ft8, T3, T4, Tp7, Tp8, T5, T6, O1, Oz, O2) placed at standard locations covering the whole scalp (the extended international 10–20 system). The reference electrode was attached to the right mastoid (A2), and the ground electrode was placed on the forehead. The procedure of recording EEG signals was the same as our previous one (Chen et al.,
Our offline data analysis was similar to our previous studies (Chen et al.,
Regarding our behavioral statistical analysis, both reaction time and accuracy were analyzed using two-way mixed analyses of variance (ANOVAs) with group (symptomatically remitted schizophrenia patients vs. healthy controls) as a between-subject factor and with condition (incongruent, congruent, and neutral) as a within-subject factor.
With regard to statistical analysis on electrophysiological data, they were analyzed according to the topographical distribution of grand averaged ERP activity as well as the methods of previous ERP studies (West and Alain,
Finally, statistical comparisons were made at
The analysis of reaction time revealed a main significant effect of condition [
Accuracy (%) | Remitted schizophrenia | 92.85 ± 1.10 | 96.15 ± 0.72 | 95.05 ± 0.86 |
Healthy controls | 93.90 ± 1.08 | 97.05 ± 0.91 | 96.60 ± 1.17 | |
Reaction time (ms) | Remitted schizophrenia | 581.62 ± 19.46 | 556.69 ± 16.80 | 562.61 ± 17.76 |
Healthy controls | 546.16 ± 19.18 | 516.49 ± 15.29 | 527.04 ± 15.15 |
Regarding accuracy, a significant main effect of condition was found [
The mean amplitude of the N450 was submitted to the four-way mixed ANOVAs with group (symptomatically remitted schizophrenia patients vs. healthy controls) as a between-subject factor, condition (incongruent, congruent, and neutral), hemisphere (left, midline, and right), and region (frontal, fronto-central, and central) as within-subject factors. The results revealed a significant main effect of condition [
The mean amplitude of the SP was submitted to the four-way mixed ANOVAs with group (symptomatically remitted patients with schizophrenia vs. healthy controls) as a between-subject factor, condition (incongruent, congruent, and neutral), hemisphere (left, midline, and right), and region (parieto-central and parietal) as within-subject factors. The results revealed a significant main effect of condition [
The current study was to examine psychophysiological processes enabling individuals to concentrate on the primary task without being interfered by distracting information in symptomatically remitted patients with schizophrenia within the context of a general conceptual framework of interference control wherein such a process is supported by two psychophysiological processes: conflict detection and conflict resolution. Behaviorally, the Stroop interference effect as assessed by decreased accuracy and longer reaction time on incongruent trials than on congruent trials was found across both groups. Moreover, there was not a significant interaction between group and condition. In other words, both groups did not manifest any significant difference in behavioral performance on the classic Stroop task in the present study. Such behavioral evidence indicates a degree of functional recovery of processes supporting interference control in patients with symptomatically remitted schizophrenia. Despite such evidence, the underlying neurophysiological mechanisms by which both groups showed comparable Stroop interference is not readily apparent merely on the basis of behavioral findings. Our electrophysiological data may help shed important insights on it.
The N450 over the frontal, fronto-central, and central regions has shown to be preferentially related to early Stroop interference effect (West and Alain,
In addition to the early Stroop interference effect, we further characterized the late Stroop interference effect in symptomatically remitted schizophrenia patients. Our ERP data revealed that the amplitude of the SP elicited by incongruent trials over the parieto-central and parietal regions was significantly increased in symptomatically remitted schizophrenia patients compared with healthy controls. This is in contrast to findings showing the absent of the SP in the acute phase of schizophrenia patients (Mcneely et al.,
These findings may have important implications for evaluating and developing the effectiveness of schizophrenia therapeutics during clinical remission. Cognitive deficits have been recognized as an important target in schizophrenia therapeutics. Our electrophysiological evidence of compensatory brain mechanisms underlying interference control adds to increasing evidence showing functional recovery of attentional-related processes and therefore contributes to describing characteristics of cognitive functions in schizophrenia therapeutics during clinical remission. Furthermore, these findings in the present study may also provide sensitive and reliable biomarkers to evaluate treatment effects and effectiveness of remediation or training approaches in schizophrenia therapeutics during clinical remission.
Although our data provide important insights into the psychophysiological correlates of interference control in symptomatically remitted patients with schizophrenia, the current study has some limitations. First, only male symptomatically remitted schizophrenia patients were included in the current study. As such, this leaves an open question concerning whether similar observations could be found in female symptomatically remitted schizophrenia patients. Given that it has been shown that gender differences exist in several aspects of schizophrenia (Häfner,
To conclude, the aim of the current study was to characterize event-related potential correlates of interference control in symptomatically remitted patients with schizophrenia. The behavioral results clearly demonstrated comparable Stroop interference performance across both groups. Furthermore, our electrophysiological data revealed a reduced N450 associated with conflict detection in conjunction with an increased SP related to conflict resolution in symptomatically remitted patients with schizophrenia. This may suggest existing compensatory brain activity as a mechanism for a degree of functional recovery of interference control in remitted patients. Together, our findings are the first to show the neurophysiological mechanism underlying functional recovery of attentional-related processes in schizophrenia during clinical remission. Our results may have important implications for evaluating and developing the effectiveness of schizophrenia therapeutics during clinical remission.
GC and YL designed the experiment; GC, LZ, WD, ZJ, and HC performed the experiment; WD and ZJ analyzed behavioral data; GC and YL analyzed ERP data; YL wrote the manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We thank our participants who participated in our study. This work was supported by the National Natural Science Foundation of China (grant number: 31600929 to YL) and Cultivation Program of Medical Science and Technique Program for Young Scientists (grant number: 14QNP006 to GC and YL).
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