title: Neural mechanisms of time-based prospective memory: evidence for transient monitoring.
abstract: In daily life, we often need to remember to perform an action after, or at, a specific period of time (e.g., take pizza out of oven in 15 minutes). Surprisingly, little is known about the neural mechanisms that support this form of memory, termed time-based prospective memory (PM). Here we pioneer an fMRI paradigm that enables examination of both sustained and transient processes engaged during time-based PM. Participants were scanned while performing a demanding on-going task (n-back working memory), with and without an additional time-based PM demand. During the PM condition participants could access a hidden clock with a specific button-press response, while in the control condition, pseudo-clocks randomly appeared and were removed via the same response. Analyses tested for sustained activation associated with the PM condition, and also transient activation associated with clock-checks and the PM target response. Contrary to prior findings with event-based PM (i.e., remembering to perform a future action when a specific event occurs), no sustained PM-related activity was observed in anterior prefrontal cortex (aPFC) or elsewhere in the brain; instead, transient clock-related activity was observed in this region. Critically, the activation was anticipatory, increasing before clock-check responses. Anticipatory activity prior to the PM target response was weaker in aPFC, but strong in pre-Supplementary Motor Area (pre-SMA; relative to clock-check responses), suggesting a functional double dissociation related to volitional decision-making. Together, the results suggest that aPFC-activity dynamics during time-based PM reflect a distinct transient monitoring process, enabling integration of the PM intention with current temporal information to facilitate scheduling of upcoming PM-related actions.
authors.affiliation: Washington University in St. Louis, St. Louis, Missouri, United States of America.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Oksanen
authors.affiliation: Washington University in St. Louis, St. Louis, Missouri, United States of America.
authors.forename: Emily R
authors.initials: ER
authors.lastname: Waldum
authors.affiliation: Washington University in St. Louis, St. Louis, Missouri, United States of America.
authors.forename: Mark A
authors.initials: MA
authors.lastname: McDaniel
authors.affiliation: Washington University in St. Louis, St. Louis, Missouri, United States of America.
authors.forename: Todd S
authors.initials: TS
authors.lastname: Braver
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology; D001931:Brain Mapping; D003071:Cognition / Q000502:physiology*; D065786:Delay Discounting / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D061212:Memory, Episodic; D008570:Memory, Short-Term / Q000502:physiology; D017397:Prefrontal Cortex / Q000033:anatomy & histology / Q000502:physiology*; D011930:Reaction Time; D013997:Time Factors