Linking neurophysiological and neuropsychological measures for aphasia assessment.

OBJECTIVES: The objective of this study was to find the event-related brain potential (ERP) waveform features and parameters that maximize the correlation between the ERP components and behavioral performance on a neuropsychological test of language comprehension (PPVT-R) in order to develop an electrophysiological diagnostic technique that can be used in the assessment of aphasic patients.
METHODS: ERPs were recorded during a computerized version of the Peabody Picture Vocabulary Test-Revised (PPVT-R, Form M). In the computerized version, a picture is presented followed by a congruent or incongruent spoken word. A derived measure was calculated from the ERP differentiation between congruent and incongruent words. The traditional PPVT-R (Form L) was also administered for comparison purposes. The participants included 10 left-sided stroke patients.
RESULTS: The N400 was the primary component elicited to incongruent spoken words. Following optimization procedures, a statistical correlation (Pearson r=0.86) was found between the derived N400 measures and the neuropsychological test scores. Examination of the scatter plot confirmed that the relationship was linear. The derived N400 measure was defined primarily as the mean of the t-scores obtained from the incongruent and congruent waveform comparison, within the temporal interval that encompasses the N400.
CONCLUSIONS: This novel quantification technique links ERPs with neuropsychological data at an unprecedented level. Given the high correlation, a regression line could reasonably be used to estimate a patient's language ability using only ERPs. However, before these findings can be accepted fully, these results need to be replicated in larger samples and across other paradigms.