Slower Postencoding Stimulus Reaction Time Predicts Poorer Subsequent Source Memory and Increased Midline Cortical Activity

Individuals vary widely in their ability to encode and retrieve past personal experiences in rich contextual detail (episodic memory). However, it remains unclear how within-subject variations in attention, measured on a trial-by-trial basis at encoding, and between-subject variation in attention and executive function abilities affect encoding-related brain activity and subsequent episodic retrieval. In the present study, 38 healthy young adults (mean age = 26.5 ± 4.4 years, 21 female) completed a task fMRI study in which they were instructed to encode colored photographs of everyday objects and their left/right spatial location. In addition, participants were asked to respond as quickly as possible to a central fixation cross that expanded in size at a variable duration after each encoding trial. RTs to the fixation cross preceding and following the object were hypothesized to reflect attentional variations pre- and postencoding stimulus, respectively. A mixed-effects logistic regression was performed to predict source memory success from pre- and poststimulus RT. Slower poststimulus RT, but not prestimulus RT, predicted poorer subsequent source memory within-subject. In addition, between-subject variation in task-switching ability, self-reported cognitive failures, and self-reported attentional abilities affected the association between poststimulus RT and subsequent memory. In addition, trial-by-trial task fMRI analysis indicated that increased encoding activity within default mode network regions was associated with slower poststimulus RT and with subsequent source retrieval failures. These results shed light onto the cognitive and neural factors that contribute to within-subject and between-subject variations in source memory ability.