Neuroanatomical Contributions to Individual Differences in P300 Morphology

Abstract

The P300 or P3 component of the event-related brain protential (ERP) is produced when subjects attend and discriminate stimulus events which differ from one another on some dimension. It is a large (ca. 10–20 µV), positive-going potential with a latency of approximately 300 ms when elicited with a simple auditory discrimination task, and is of maximal amplitude over the midline central and parietal scalp areas (Donchin et al. 1986; Pritchard 1981). Although the neural orgins of the P3 are still being sought, depth electrode recordings, and magnetic field studies in human suggest that at least some aspect of the P3 is generated in the medial temporal lobe areas, most likely including portions of the hippocampus (Halgren et al. 1980; McCarthy et al. 1982; Okada et al. 1983). Since these areas have been associated with learning and memory, the P3 has been linked to fundamental brain events involved with memory-updating processes. This theoretical interpretation has been supported by a variety of studies which have demonstrated changes in the P3 that reflect differential memory performance between experimental conditions (Fabiani et al. 1985; Johnson et al. 1985; Karis et al. 1984; Neville et al. 1986), as well as individual differences for normal and impaired cognitive function (Brown et al. 1982; Howard and Polich 1985; Polich et al. 1983, 1986; Squires et al. 1979). However, because the P3 is sensitive to these cognitive brain events, wide individual variation exists in its overall morphology and timing. This chapter will review some of the initial studies which have attempted to determine the sources of this individual variability in the P3 component of the ERP.