Structural correlates of commission errors in prospective memory.

Prospective memory refers to remembering to perform an intended future action, such as remembering to take medication with breakfast. Historically, the field has focused on failures to initially remember a prospective memory task (omission errors), but interestingly, individuals will occasionally repeat a prospective memory action after it has been completed (e.g., double dosing). These failures in prospective memory deactivation/forgetting are termed commission errors. The current registered study investigated structural neuroimaging correlates of a laboratory measure of commission errors in 47 healthy older adults. Extant theories differed in their predicted outcomes: commission error risk was predicted to be highest in individuals with smaller medial temporal lobe volume (output monitoring theory), larger lateral prefrontal cortex volume (residual activation theory), or a combination of larger medial temporal lobe volume and smaller lateral prefrontal cortex volume (dual mechanisms theory). In registered analyses, we found that a higher number of commission errors was associated with larger medial temporal lobe/hippocampal grey matter volume (supporting dual mechanisms theory), but not with grey or white matter volume in the lateral parietal lobe, frontal pole, or a composite of ventrolateral/dorsolateral prefrontal cortex (not supporting dual mechanisms theory). In post hoc analyses, smaller volume in the lateral orbitofrontal cortex was associated with a higher number of commission errors, possibly indicating that the dual mechanisms theory of PFC control was conceptually correct, but that a different PFC subregion than anticipated exerts control over commission errors. Collectively, the registered and post hoc analysis findings showed a functional dissociation across MTL/PFC regions that was more consistent with the dual mechanisms theory than the alternative theories.