Decision Making Journal Club

The classic P300 encodes a build-to-threshold decisionvariable

The P300 component of the human event-related potential has been the subject of intensive experimental investigation across afive-decade period, owing to its apparent relevance to a wide range of cognitive functions and its sensitivity to numerous braindisorders, yet its exact contribution to cognition remains unresolved. Here, we carry out key analyses of the P300 elicited by tran-sient auditory and visual targets to examine its potential role as a ‘decision variable’ signal that accumulates evidence to a deci-sion bound. Consistent with the latter, we find that the P300 reaches a stereotyped amplitude immediately prior to responseexecution and that its rate of rise scales with target detection difficulty and accounts for trial-to-trial variance in RT. Computationalsimulations of an accumulation-to-bound decision process faithfully captured P300 dynamics when its parameters were set bymodel fits to the RT distributions. Thus, where the dominant explanatory accounts have conceived of the P300 as a unitary neuralevent, our data reveal it to be a dynamically evolving neural signature of decision formation. These findings place the P300 at theheart of a mechanistically principled framework for understanding decision-making in both the typical and atypical human brain.