Schizophrenia is described as an incapacitating, chronic and severe mental illness which affects about 1% of the population. Among the most frequently prominent of the cognitive symptoms in schizophrenia are deficits in working memory. More recently, individuals at ultra-high risk (UHR) of psychosis have been proposed to help provide awareness on the nature of prodromal stages and further acknowledge the initial stages to offer possibilities for early and more distinct interventions. It is particularly critical to perform studies on UHR of psychosis subjects as around 30% of UHR people experience progression into psychosis within two years.
A pilot study was conducted (8 females, 4 males) to examine visual P300 amplitude and detect hippocampal activity through scalp EEG, using the ICA analysis methodology. A smaller separate study was also conducted amongst UHR subjects (3 males, 1 female) and controls (2 males, 1 female).
Findings revealed a pattern of high amplitude positivity across the ipsilateral anterior basal temporal, and mid parietal electrodes, alongside a low amplitude positivity, distributed around the cheekbones; similar patterns were identified in UHR subjects. UHR subjects displayed a higher P300 amplitude compared to controls, contrary to previous findings.
The results of the present study provide a stepping stone for future studies to conduct further research incorporating additional source localisation analysis such as sLORETA. Understanding the location of the source of the P300 could allow prospective studies to determine and predict conversion to psychosis and act as possible biomarkers of psychosis amongst individuals with UHR, allowing a platform to provide early interventions for these at-risk individuals.
Table of Contents
Introduction
Schizophrenia and Visual Working Memory
Ultra-High-Risk of psychosis
Ultra-High-Risk of psychosis and Visual Working Memory
Hippocampus and Visual Working Memory
Hippocampal Impairments in Schizophrenia
The P300 event related potential
P300 Impairments in Schizophrenia
The P300 as a putative biomarker of psychosis risk
Detecting hippocampal activity through scalp EEG
Rationale, Aims and Hypotheses
Methods
Participants
Pilot study sample
PSYSCAN study sample
Inclusion and exclusion criteria
Ethical considerations
Visual Working Memory Task (based on Hannula, 2015)
Design and Procedure
EEG Data Acquisition and analysis
ERP Processing
Statistical Analysis
Results
Pilot Study Analysis
Demographics
ERPs
Visual Analysis of EEG 3D Amplitude Maps
Power Analysis
PSYSCAN Study Analysis
Demographics
ERPs
Independent samples t-test
Visual Analysis of EEG 3D Amplitude Maps
Discussion
P300 ERP components in a visual working memory task
Mesial sources contribution to scalp EEG
Hippocampus activation and Visual Working Memory
P300 ERP in UHR subjects
Hippocampal activity detection in UHR subjects
Strengths of the current study
Limitations of the current study
Future directions
Conclusion
Objectives and Topics
This research aims to investigate the neurobiological basis of visual working memory (VWM) deficits in individuals at ultra-high risk (UHR) for psychosis by utilizing the P300 event-related potential (ERP) as a biomarker and attempting to detect hippocampal activity through scalp EEG. The primary research question centers on whether hippocampal activity can be delineated during VWM tasks and if differences in P300 amplitude and latency exist between UHR individuals and healthy controls.
- Visual Working Memory (VWM) in schizophrenia and UHR subjects
- Hippocampal function and its contribution to scalp EEG signals
- The P300 ERP as a potential physiological biomarker for psychosis risk
- Methodological application of Independent Component Analysis (ICA) for source delineation
Excerpt from the book
Mesial sources contribution to scalp EEG
The involvement of mesial temporal sources to scalp EEG has been a matter of dispute ever since the arrival of EEG and SEEG recordings (Abraham and Ajmone-Marsan, 1958), yet has continued to be unclear. This may be ascribed to the neurophysiological difficulty in accurately unravelling the contribution of mesial from neocortical sources to scalp EEG signals. The classical inverse problem in EEG is occupied with identifying the locations and strengths of the existing courses. However, studies using the EEG method that have attempted to identify specific areas of the brain that could be responsible for generating the P300 component concluded that it is very difficult. Nevertheless, in our pilot study, we achieved to detect activity emanating from the hippocampus from 6 samples. A pattern of high amplitude positivity in the ipsilateral anterior basal temporal electrodes (F9-FT9 or F10-FT10) and mid parietal electrodes (P3 and P4), alongside a low amplitude positivity distributed around the cheekbones.
These results are in line with the findings from a previous study who analysed simultaneous scalp and intracerebral EEG recordings in epileptic patients, to allocate the involvement of mesial temporal sources to scalp EEG (Koessler et al., 2015). The findings of this study discovered that the corresponding scalp EEG spikes of mesial networks continually exhibited a significant negativity recorded in the ipsilateral anterior basal temporal electrodes. This study, from our knowledge, is the only study that has successfully detected hippocampal activity using scalp EEG simultaneously to intracranial recordings. These findings supplementary to the results of the current pilot study helps support the notion that mesial temporal sources do not produce closed electrical fields notwithstanding the folding of the hippocampus and the opposing alignment of the subiculum and parahippocampal gyrus (Jayakar et al., 1991).
Summary of Chapters
Introduction: Provides a comprehensive overview of cognitive deficits in schizophrenia, the specific challenges in visual working memory, and the clinical importance of the ultra-high-risk (UHR) state for early intervention.
Methods: Details the recruitment of participants, ethical considerations, the design of the visual working memory task, and the specific EEG data acquisition and preprocessing steps, including ICA.
Results: Reports the findings from both the pilot study and the PSYSCAN study, focusing on P300 amplitude and latency differences and the visual analysis of EEG 3D amplitude maps to localize hippocampal activity.
Discussion: Interprets the findings regarding P300 components, the successful detection of mesial temporal activity via scalp EEG, and compares results with previous literature to highlight the role of the hippocampus in VWM.
Conclusion: Summarizes the methodology as a stepping stone for future research into biomarkers of psychosis and emphasizes the potential of utilizing sLORETA for further source localization.
Keywords
Schizophrenia, Ultra-High-Risk (UHR), Visual Working Memory (VWM), P300, Hippocampus, Electroencephalography (EEG), Independent Component Analysis (ICA), Biomarkers, Cognitive deficits, Event-related potentials (ERP), Neurodevelopmental model, Prodromal stages, Source localization, Psychosis, Mesial temporal sources.
Frequently Asked Questions
What is the primary objective of this research dissertation?
The research aims to delineate hippocampal activity during visual working memory tasks and explore whether P300 ERP components can serve as biomarkers for individuals at ultra-high risk (UHR) for psychosis.
Which key areas are examined in this study?
The study examines the cognitive deficits in schizophrenia, the specific nature of UHR psychosis, the role of the hippocampus in working memory, and the electrophysiological properties of the P300 component.
What is the central research hypothesis?
The study hypothesizes that P3a and P3b ERPs can be detected using a VWM task, that UHR subjects will show reduced P300 amplitudes and delayed latencies compared to controls, and that hippocampal activity is detectable via cheekbone electrodes.
What scientific methodology is utilized?
The research utilizes cross-sectional scalp EEG, applying Independent Component Analysis (ICA) to preprocess signals and detect artifacts, combined with visual analysis of 3D amplitude scalp maps.
What does the main body of the work address?
The main body details the experimental procedures, data acquisition from both a pilot study and the PSYSCAN study, and provides a statistical analysis comparing ERP waveforms between UHR subjects and healthy controls.
Which keywords characterize this work?
Key terms include Schizophrenia, Ultra-High-Risk, P300, Hippocampus, EEG, ICA, VWM, and biomarkers.
Why is the hippocampus significant in this study?
The study investigates the hippocampus because empirical evidence links it to working memory maintenance of novel items, and the researchers aim to identify its activity through non-invasive scalp EEG, which is typically considered difficult.
What were the findings regarding hippocampal activity in UHR subjects?
The study successfully detected a similar pattern of hippocampal activity in UHR participants as in the pilot sample, occurring between the 310-350 millisecond time window, suggesting its involvement in the retention of visual information.
How does this study contribute to existing literature?
It provides a potential methodology for identifying mesial temporal activity using only scalp EEG and offers new insights into how visual working memory tasks can be used to elicit responses from the hippocampus in at-risk populations.
- Citation du texte
- Sidra Shahzad (Auteur), 2017, Propagation of hippocampal activity in ultra-high risk schizophrenia psychosis subjects using Independent Component Analysis, Munich, GRIN Verlag, https://www.grin.com/document/418222
