Interactions Between Forms of Memory: When Priming Hinders New Episodic Learning

1. Interactions Between Forms of Memory:When Priming Hinders New Episodic Learning Anthony D. Wagner, Anat Maril, and Daniel L. Schacter Journal of Cognitive Neuroscience, 2000 Wei-Chung Lee April 25, 2001

2. Forms of Memory Long Term Memory Explicit (Declarative) Implicit (Non-declarative) Semantic (Facts) Episodic (Events) Priming Procedural Associative Learning Nonassociative Learning Emotional responses Skeletal musculature Medial temporal lobe Neocortex Striatum Amygdala Cerebellum Reflex pathways

3. Long Term Memory Explicit (Declarative) Implicit (Non-declarative) Semantic (Facts) Episodic (Events) Priming Procedural Associative Learning Nonassociative Learning Emotional responses Skeletal musculature Medial temporal lobe Neocortex Striatum Amygdala Cerebellum Reflex pathways Motivation • When and how do these different forms of memory interact? ?

4. Episodic Memory • Explicit memory for conscious recollection of events from past experience Buckner and Koustaal, 1998

5. Perceptual Repetition Priming • Facilitation derived from repeated exposure to a stimulus Buckner et al., 1998

6. Long Term Memory Explicit (Declarative) Implicit (Non-declarative) Semantic (Facts) Episodic (Events) Priming Procedural Associative Learning Nonassociative Learning Emotional responses Skeletal musculature Medial temporal lobe Neocortex Striatum Amygdala Cerebellum Reflex pathways Hypothesis • Priming for past experiences can hinder new episodic encoding.

7. Predictions • Enhanced behavioral and neural priming during re-encoding with a shorter (2 min.) relative to a longer (25 hr.) lag between two encoding episodes. • Impaired long-term retention of episodic memory in conditions with greater behavioral and neural priming. • Lag Effect: shorter lags between repetitions deleterious to explicit memory (Ebbinghaus, 1885).

8. Experimental Procedure • Varied temporal lag between initial and repeated encoding episodes with words.

9. Behavioral Priming • Mean median Reaction Times (RTs) for Abstract/Concrete decision (msec). • Once-presented: 777 • Long-Lag: 763 • Short-Lag: 720 * ** ** ** * p < 0.09** p < 0.0001

10. Neural Correlates of Episodic encoding and Repetition Priming Once-presented > Fixation Once-presented > All Re-encoding • A subset of regions activated by episodic encoding demonstrate a significant repetition priming effect (i.e.. decrease in activation): anterior-LIPC, posterior-LIPC, and left fusiform cortex.

11. Lag Effects on ROI Activation • Long-Lag > Short-Lag • Priming also effects activation in left frontal operculum, left middle frontal, and medial frontal regions (Data not shown) • Greater neural correlate of priming during re-encoding following a shorter temporal lag rather than long

12. Explicit Memory • Explicit memory scores = (pHit - pFalse alarm) • Overall (High & Low Confidence) pHit • Long-Lag 35% 77% • Short-Lag 31% 73% • Once-Presented 22% 64% • “High Confidence” explicit memory • Long-Lag 32% 46% • Short-Lag 25% 38% • Once-Presented 17% 30% * ** ** ** ** ** * p < 0.005** p < 0.0001

13. Priming Negatively Correlates with Subsequent Explicit Memory • A negative association across-subjects between behavioral & neural (posterior & anterior-LIPC shown) priming and subsequent explicit memory. • Reliable correlations not found for Short-Lag trials(highest levels of priming led to lowest levels of “High Confidence” => range too small)

14. Conclusions • Correlation of behavioral and neural measures of priming during the re-encoding of a stimulus and impaired episodic encoding. • “cross-talk” between implicit and explicit forms of memory. • Posited mechanism: Priming reduces “encoding variability” or multiple retrieval routes increasing the probability that same task-relevant stimulus features ...

15. Implications & Questions • Consolidation? Time course of Lag Effect; optimal time to re-encode? • Attention? • 1 L neocortex  1x106 neurons  1x109 synapses and 1 voxel  • Segregation of memory types justified? • Activation maps show significant differences in Blood Oxygenation Levels. • Encoding versus re-encoding • Not encoding/re-encoding the same words between sessions - may evoke different “meanings”/saliencies.