Multimodal characterization of the semantic N400 response within a rapid evaluation brain vital sign framework

Abstract

BackgroundFor nearly four decades, the N400 has been an important brainwave marker of semantic processing. It can be recorded non-invasively from the scalp using electrical and/or magnetic sensors, but largely within the restricted domain of research laboratories specialized to run specific N400 experiments. However, there is increasing evidence of significant clinical utility for the N400 in neurological evaluation, particularly at the individual level. To enable clinical applications, we recently reported a rapid evaluation framework known as “brain vital signs” that successfully incorporated the N400 response as one of the core components for cognitive function evaluation. The current study characterized the rapidly evoked N400 response to demonstrate that it shares consistent features with traditional N400 responses acquired in research laboratory settings—thereby enabling its translation into brain vital signs applications.MethodsData were collected from 17 healthy individuals using magnetoencephalography (MEG) and electroencephalography (EEG), with analysis of sensor-level effects as well as evaluation of brain sources. Individual-level N400 responses were classified using machine learning to determine the percentage of participants in whom the response was successfully detected.ResultsThe N400 response was observed in both M/EEG modalities showing significant differences to incongruent versus congruent condition in the expected time range (p < 0.05). Also as expected, N400-related brain activity was observed in the temporal and inferior frontal cortical regions, with typical left-hemispheric asymmetry. Classification robustly confirmed the N400 effect at the individual level with high accuracy (89%), sensitivity (0.88) and specificity (0.90).ConclusionThe brain vital sign N400 characteristics were highly consistent with features of the previously reported N400 responses acquired using traditional laboratory-based experiments. These results provide important evidence supporting clinical translation of the rapidly acquired N400 response as a potential tool for assessments of higher cognitive functions.

Brain Vital Signs Detect Information Processing Differences When Neuromodulation Is Used During Cognitive Skills Training

“…However, conventional ERP methodology and subsequent analyses are typically complex and time-consuming. To translate this laboratory capability into clinical applications, our group developed and validated a rapid evaluation platform known as the “brain vital signs” framework (Ghosh et al, 2016 , 2018 ; Fickling et al, 2019 ). The brain vital signs framework employs a portable, low-density EEG system with automated, user-friendly software that facilitates the quick assessment of several key ERPs serving as brain function indicators.…”

“…Out of the 60 sets of primed word pairs, half are congruent and half are incongruent. Of particular interest to the current study, the N400 indexes high-level cognitive processes during semantic processing (Kutas and Hillyard, 1980 ; D’Arcy et al, 2004 , 2005 ; Kutas and Federmeier, 2010 ; Ghosh et al, 2018 ). Together, the N100, P300, and N400 measurements of brain function provide enhanced sensitivity to track cognitive changes in the brain.…”

Brain Vital Signs Detect Cognitive Improvements During Combined Physical Therapy and Neuromodulation in Rehabilitation From Severe Traumatic Brain Injury: A Case Report

“…The brain vital signs framework (Ghosh Hajra et al, 2016 , 2018a ; Fickling et al, 2019 ) provides a rapid evaluation of evoked brain responses through quantified EEG, extracted as event-related potentials (ERPs). ERPs provide an objective, physiological measure of cognitive function (Gawryluk and D’Arcy, 2010 ; Luck, 2014 ).…”

Effect of the number of training trials on the event-related potential correlates of equivalence relations

“…To date, the ERP considered to be the "brainwave marker of semantics processing" (cf. Hajra et al, 2018) is the N400, a negative-going wave that peaks at approximately 400 ms following the stimulus-stimulus pairing presentation. In an experimental setup with a series of semantically related word pairs (e.g., chair-table) and unrelated word pairs (e.g., chair-lion), an across-trial comparison of ERP signals shows a clear differentiation in the range of the N400 evoked by related and unrelated word pairs.…”