Developing an ERP Paradigm to Assess Conceptual Processing in Doc Patients: A Proof of Principle Study

Abstract

Severe acquired brain damage can sometimes result in a set of conditions resulting in altered states of consciousness, called Disorders of Consciousness (DOC). Event-related potentials (ERPs) extracted from electroencephalography (EEG) have proven to be a reliable neuroimaging method to accurately diagnose and predict the outcome of patients with DOC. The N400 component indicates higher order cognitive activity associated with processing, including language, music, and environmental sounds. An increased N400 amplitude has mainly been observed in response to sentence and word priming paradigms, mostly from healthy and native speakers of the language. Stimuli like sentences can tax working memory, which can cause misinterpretation of a patient’s condition as reflecting a language dysfunction when, in fact, the problem is about memory. Environmental sounds, or sounds related to common events, encode conceptual meanings similar to language and could be easier for such patients to comprehend. This study introduces a unimodal auditory priming paradigm with environmental sounds and spoken words to investigate if significant N400 activity could be elicited in a sample of 18 healthy participants and one DOC patient. ERP components (N400, N100 and P200) were extracted and averaged across 18 participants, as well as collected individually from each participant and one patient. The environmental sounds were paired with conceptually congruent and incongruent words. Comparisons of amplitude and latency were made between congruent and incongruent conditions. Statistical analysis indicated that the N400 amplitude peak in response to incongruent sound-word pairs was significantly higher than the responses to the congruent sound-word pairs across the grand average of 18 participants and for each individual participant as well. Significant differences for the amplitude and latency of N100 and P200, components that indicate auditory processing were seen across the average of 18 participants. The DOC patient showed a possible N400 effect upon visual inspection. Further testing of this paradigm with more non-communicative patients with neurological dysfunction is required to determine the utility of this priming paradigm in clinical protocol for diagnostic and prognostic purposes.