Prospective memory: encoding and retrieval

Sam Gilbert

Institute of Cognitive Neuroscience

Background

• Prospective memory (PM) refers to our ability to encode intentions for future behaviour, then act on those intentions at the appropriate time

• Several recent fMRI studies have investigated brain mechanisms supporting this ability (Benoit et al., in prep; Burgess et al., 2001, 2003; Gilbert et al., in press; Okuda et al., 1998, 2007; Reynolds et al., in press; Simons et al., 2006)

• These studies have all investigated retrieval of delayed intentions. The present study will look at encoding as well

Previous studies

• Typically, participants are engaged in an “ongoing task”, e.g. making a button-press response to a series of words to indicate whether they have 4 or 6 letters

• PM conditions: continue performing the ongoing task, but press a different button if you see an animal word

PM > ongoing only ongoing only > PM

Burgess et al., 2001 Burgess et al., 2003

Design

SONG

REST

SONG

WEAR

REST

WEAR

SWIM

CASE

NOTE

Ongoing task: 2-back

yes

no

no

yes

no

no

no

PM encode

PM store (1 – 5 trials)

PM retrieve: press different key

SWIM no

Control: PM encode

Control: PM store (1 – 5 trials)

Control: PM retrieve

Analyses

• PM storage trials versus control: expect signal change in BA 10• PM encoding versus control: same regions as involved in retrieval?• Subsequent prospective memory effect: encoding-related activity

that distinguishes subsequent hits from misses?• Each PM cue will appear twice in the experiment. Half of blocks use

words, half pictures. Multi-voxel pattern analysis to find out whether the intention can be decoded from storage trials (specific intention / word versus picture)

Methods

• Standard EPI imaging parameters: 3mm x 3mm x 3mm voxels, 33 slices, TR=2.5s

• 3s per trial; 7 trials per ‘miniblock’ (i.e. PM or control), total: 48 PM, 48 control trials

• 6 runs of approx 6 minutes + 6 minute structural scan: total scanner time = 42 mins

• Analysis in SPM5