Development of an Experimental EEG Paradigm to Investigate Dysfunctions in Schizophrenia: Predicting the Sensory Consequences of One’s Own Actions
Background: Prediction mechanisms are crucial for efficient perception of the environment and ourselves as well as for discrimination between self-generated and external changed situations. Known as the internal forward model, an efference copy of the motor plan prepares the sensory areas for the r...
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| Format: | Dissertation |
| Sprache: | Englisch |
| Veröffentlicht: |
Philipps-Universität Marburg
2023
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| Zusammenfassung: | Background:
Prediction mechanisms are crucial for efficient perception of the environment and ourselves as well as for discrimination between self-generated and external changed situations. Known as the internal forward model, an efference copy of the motor plan prepares the sensory areas for the reafferent feedback of one’s own planned actions. In case of a match between predicted and actual sensory feedback, further processing of the sensory consequences can be damped. This can be seen in suppressed N1-ERP amplitudes in EEG as well as attenuated intensity perception in behavioural data. Moreover, agency for self-generated actions can be attributed correctly by means of this mechanism, whereas external actions cannot prepare the sensory cortex with efference copy and therefore are identified as externally-generated. Dysfunctions in the prediction mechanism for self-generated actions result in a mismatch in the internal forward model, which in turn results in external attribution of agency as well as abnormal neurophysiological and behavioural correlates. Disturbed prediction mechanisms and failure in efference copy are suggested to be a reason for several positive symptoms of schizophrenia like sensory hallucinations and passivity experiences.
Hypotheses/Objective:
In the first part of our study, we investigated efference copy based predictions in healthy subjects in an extensive button press experiment. We hypothesised that the analyses of a selected number of visual trials with the same intensity will be sufficient to show N1-ERP suppression in active conditions. We expected that the second stimulus is perceived as more intense significantly more often in active conditions. With the main aim to develop an optimised and suitable experiment for patients, we hypothesised clearer N1-ERP and behavioural effects after changing the experimental setup in the second part of our study by altering the time intervals, shortening the overall duration, changing the presentation format and focussing on the visual condition only. Finally, we suggested that participants are able to perform the optimised task well. We expected this to be evidenced by the Post-Experiment Questionnaire.
Material and Methods:
Participants pressed actively or passively a button followed by visual stimuli displayed on a computer monitor. Consequently, they judged whether the first or second stimulus was brighter by pressing one of the defined keys. For the total duration of the experiments, we recorded EEG. Additionally, participants were asked to complete a questionnaire about the optimised experiment to assess the performance and suitability.
Results:
For both experiments, we found significantly smaller N1 peak values in active trials than in passive conditions in healthy subjects. The difference between the two experiments themselves was not significant. Behavioural data for intensity perception showed no significant difference, neither in the individual experiments nor in comparing the two. In patients with schizophrenia, we found no significant results for the optimised experiment. However, patients as well as healthy subjects were able to perform well in the optimised experiment assessed by the Post-Experiment Questionnaire.
Discussion:
Our electrophysiological results go in line with prior research in healthy subjects in both experiments. We showed that the analyses of a selected number of visual trials with the same intensity was sufficient to show N1-ERP suppression in active conditions in the extensive experiment. In contrast to our expectations for the behavioural task, we did not find a significant difference between the two conditions for both experiments. This stands in contrast to the under¬standing of sensory attenuation that self-initiated actions perceived as less intense than external ones. Therefore, further changes and studies are needed to show more robust effects for the visual system whereas most of the former studies focus on the other sensory modalities. However, the development of an EEG study which is suitable for patients with schizophrenia was successful regarding the Post-Experiment Questionnaire data.
Conclusion:
In conclusion, we demonstrated evidence of the neural (but not behavioural) mechanism in the visual modality. With the main aim to develop an experimental paradigm for patients to investigate dysfunctions in schizophrenia, we showed the suitability of the task assessed by the Post-Experiment Questionnaire. Further studies with a larger sample of patients are required to give more insight into the psychopathology and impaired predictive mechanisms in the visual domain in schizophrenia. |
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| DOI: | 10.17192/z2023.0554 |