Free recall (FR) is a ubiquitous internally-driven retrieval operation that crucially affects our day-to-day life. The neural correlates of FR, however, are not sufficiently understood, partly due to the methodological challenges presented by its emerging property and endogenic nature. Using fMRI and performance measures, the neuro-behavioral correlates of FR were studied in 33 healthy participants who repeatedly encoded and retrieved word-lists. Retrieval was determined either overtly via verbal output (Experiment 1) or covertly via motor responses (Experiment 2). Brain activation during FR was characterized by two types of performance-based parametric analyses of retrieval changes over time. First was the elongation in inter response time (IRT) assumed to represent the prolongation of memory search over time, as increased effort was needed. Using a derivative of this parameter in whole brain analysis revealed the default mode network (DMN): longer IRT within FR blocks correlated with less deactivation of the DMN, representing its greater recruitment. Second was the increased number of words retrieved in repeated encoding-recall cycles, assumed to represent the learning process. Using this parameter in whole brain analysis revealed increased deactivation in the DMN (i.e., less recruitment). Together our results demonstrate the naturally occurring dynamics in the recruitment of the DMN during utilization of internally generated processes during FR. The contrasting effects of increased and decreased recruitment of the DMN following dynamics in memory search and learning, respectively, supports the idea that with learning FR is less dependent on neural operations of internally-generated processes such as those initially needed for memory search.
|Number of pages||12|
|State||Published - Jul 2012|
Bibliographical noteFunding Information:
We thank Orit Stern, Eti Ben Simon, Vicki Myers, Ilana Podlipsky and Fabrizio Esposito for helpful comments on this manuscript and Oren Levin, Keren Rosenberg and Noga Oren for technical and data analysis assistance. The study was supported by a post-doctoral fellowship and a Young Investigator Research Grant from The National Institute for Psychobiology in Israel to I-S.L. Corresponding author: Irit Shapira-Lichter, Functional Brain Imaging Unit, Wohl Institute for Advanced Imaging, Tel-Aviv Sourasky Medical Center, 6 Weizmann Street, Tel Aviv 64239, ISRAEL.
- Default mode network
- Episodic memory
- Inter-response time
- Memory search