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S071-3

Lower P300 Amplitudes for Internally-Generated, But Not Externally-Generated,
Events in Schizophrenia

Mohammad Zia Ul Haq Katshu1, Priyadarshee Abhishek2, S. Haque Nizamie2, Indu Dubey3, Nishant
Goyal3, Sai Krishna Tikka2, Hariom Pachori2, Devvarta Kumar4, Mohammad Zia Ul Haq Katshu3

1Institute of Mental Health, University of Nottingham, UK 2Central Institute of Psychiatry, India 3University of
Nottingham, UK 4 National Institute of Mental Health & Neurosciences, India

Background/Objective: Patients with schizophrenia demonstrate difficulty differentiating inner
from overt speech, reporting words thought as said loudly. This misattribution of self-generated
events to external agency extends to other domains as well, like identifying the actions of an alien
hand as their own (Woodward et al., 2007). An excessive deployment of attention to external events
as well as poor processing of self-generated events has been proposed to explain this misattribution
(Brookwell et al., 2013). This study was done to understand the neurophysiological processing of
internally-generated and externally-generated events in schizophrenia.

Method: Seventeen patients and fourteen healthy controls completed a two-stage source monitoring
task involving solving a three-letter jumbled word either by the participant or a computer following
which they had to identify the correct source of the word - solved by self (internal source monitoring,
ISM) or by computer (external source monitoring, ESM), while EEG was recorded. P300 amplitude
and latency was computed separately for both ISM and ESM conditions.

Result: P300 amplitude for the ISM condition in patients with schizophrenia was lower compared to
the ESM condition in the same group over central and parietal regions and the ISM condition in the
controls over central, parietal and temporal regions. However, P300 amplitude for the ESM condition
did not differ significantly between the two groups. In contrast to P300 amplitude, there were no
significant differences in P300 latency in the ISM or ESM condition between the two groups.

Conclusion: P300 amplitude was lower specifically for internally-generated but not
externally-generated events in patients with schizophrenia. This study provides the first specific
electrophysiological evidence of impaired source monitoring in schizophrenia.

Fig. 1. Comparison of the P300 amplitudes for Fig. 2.Comparison of the P300 latencies for
internally-generated and externally-generated evets internally-generated and externally-generated evets
between patients with schizophrenia and healthy controls between patients with schizophrenia and healthy controls
over different scalp regions (legend: l - left, r - right, f - over different scalp regions (legend: l - left, r - right, f -
frontal, c - central, p - parietal, t - tempo frontal, c - central, p - parietal, t - tempor

Reference: Woodward et al. Source monitoring biases and auditory hallucinations. Cognitive