Haemodynamic and electrophysiological markers of pragmatic language comprehension in schizophrenia

Abstract

Objectives. The present study aimed at investigating neurophysiological markers of language perception in schizophrenia using simultaneous near-infrared spectroscopy (NIRS) and event-related potentials (ERPs), which have been proven to be useful for studying language processing abilities in psychiatric patients. The study shall help to integrate previous findings from ERP and fMRI studies on figurative language comprehension in schizophrenia and elucidate how electrophysiological and haemodynamic markers of language processing are related. Methods. Twenty-two healthy subjects and 22 schizophrenia patients judged 120 sentences regarding their meaningfulness. Phrases were literal, metaphoric, or meaningless. EEG-fNIRS signals were recorded throughout the entire experiment. Results. Schizophrenia patients showed deficient and delayed sentence comprehension. Both the early N400 and left-hemispheric activation during language comprehension were altered in patients. Correlation analyses showed that metaphor-related ERPs were strongly linked to haemodynamic cortical activity in healthy subjects, but not in patients. Conclusions. Our results indicate group differences in cortical electrophysiological and haemodynamic activation that represent rather general impairments in the processing of complex language. Simultaneous EEG/NIRS applications are useful to depict these neural markers and to investigate their relationship. Future studies are needed to clarify the nature of respective anomalies and their potential as putative neural markers in schizophrenia research.

Key words::

• figurative language comprehension
• schizophrenia
• event-related potentials
• functional near-infrared spectroscopy
• inferior frontal cortex

Acknowledgements

This work was in part supported by Nachwuchsgruppe IZKF Tuebingen (2115-0-0; A.-C. Ehlis). We thank Hitachi Medical Co., Japan for providing the prototype cap for combined EEG-22-channels-NIRS-measurements and for their skilled technical support as well as Ramona Taeglich and Betti Schopp for their friendly, trustworthy and proficient technical assistance.

Statement of Interest

None to declare.

Notes

¹ Subject-based inter-optode distance measurements were performed where the combined EEG/NIRS cap was placed on n=5 heads with circumferences ranging from 54 to 58 cm and inter-optode distances for each adjacent optode-pair was assessed. These measurements revealed negligibly small inter-optode distance variations of 0.01 cm which were further limited to the upper optode rows (cf. Figure 1).

² HHB values were in accordance with the respective O2Hb data but were associated with lower statistical power and are, to preserve conciseness, presently unattended.