Sequence-sensitive subcomponents of P300: Topographical analyses and dipole source localization

P300 amplitude and reaction time (RT) are strongly affected by the sequence of events preceding the eliciting stimulus. Sommer, Leuthold and Soetens ( 1999) found that robust sequential effects in P300 amplitude could be disso ciated. from more variable sequential effects in RTs. However, global chang es in P300 amplitude and topography gave rise to the suggestion that sequen tial effects are specific for a subcomponent of P300 that is separate from and anterior to the classical parietal P300. Here, confirming evidence for dissociable subcomponents of P300 is reported from two experiments. Indepen dent component analysis separated a centrally distributed sequence-sensitiv e subcomponent from a more parietal subcomponent. Subsequent dipole source analysis indicated a deep mesial source for the sequence-sensitive subcompo nent. Overlap with reafferent somatosensory activity appears to be responsi ble for an apparent lateralization of this component towards the hemisphere ipsilateral to the responding hand.