Once the N400 was characterized as a measure – and in parallel with its use to begin to answer basic questions in language and memory – its power for studying special populations was recognized. In particular, the N400’s functional specificity offered an inroad to questions about the nature of certain deficits, at least under the right conditions (i.e., using well-tested paradigms that replicate in controls). Moreover, the N400 offered a critical opportunity to measure processing in groups with more limited abilities to meet the demands of typical cognitive tasks. Although a thorough review of the findings from studies using the N400 with special populations is beyond the scope of this piece, it is important to note that the N400 has now been used in the study of many different conditions, including Alzheimer’s disease, aphasia, autism, cerebral palsy (as a means of measuring vocabulary size), closed head injury, dyslexia (and other developmental language disabilities), epilepsy, mood disorders, Parkinson’s disease, psychopathy, and schizophrenia (reviewed in Munte et al 2000; Kuperberg in press). More generally, the N400, often in conjunction with neuropsychological measures, has been used to measure individual differences in language and memory functions in the general population, across the lifespan.
