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- Title
Effects of Left Inferior Prefrontal Stimulation on Episodic Memory Formation: A Two-Stage fMRI-rTMS Study.
- Authors
Köhler, Stefan; Paus, Tomáš; Buckner, Randy L.; Milner, Brenda
- Abstract
Successful recovery of words from episodic memory relies strongly on semantic processes at the time of encoding. Evidence from several functional magnetic resonance imaging (fMRI) studies has shown that changes in neural activity in the left inferior prefrontal cortex (LIFPFC) during semantic encoding predict subsequent memory performance. This evidence has been taken to suggest that LIPFC plays a critical role in memory formation. Functional neuroimaging findings, however, do not establish a causal brain-behavior relationship. To determine whether there is a causal link between LIPFC involvement at encoding and subsequent success in memory performance, we conducted a two-part study in which we first used FMRI to localize encoding-related activation in LIPFC and then employed repetitive transcranial magnetic stimulation (rTMS) to manipulate neural processes in LIPPFC during semantic encoding. To demonstrate the neuroanatomical specificity of any observed effect and to control for nonspecific rTMS side effects, we also stimulated neural processes in two control sites. Using frameless stereotaxy, we positioned the stimulation coil to target (1) the LIPF region that was activated during fMRI (mean. xyz = - 48:35:5); (2) the homologous right-hemisphere region; and (3) an additional left parietal control site at each site, "stimulated" items (600 msec of 7-Hz rTMS with Cadwell Round Coil) were intermixed with items presented without concurrent stimulation. Subsequently, subjects performed a recognition memory task for the words encountered. We found support for the predicted causal brain-behavior relationship, which was specific to LIPFC. When comparing recognition scores for stimulated items, normalized for variations in performance on normalised trails, we found that words encoded under LIPFC stimulation were subsequently recognized with higher accuracy than words encoded under stimulation in the two corticals control sites. By contrast, no performance difference emerged when the two control sites were compared with each other. Based on additional analyses of the rTMS effects observed directly at the time of encoding ( i.e., on semantic-decision performance), we suggest that LIPFC stimulation may have produced its effect on recognition memory, at least in part, through the triggering of more extensive processing of the stimulated items and an ensuing gain in item distinctiveness. Physiological process of facilitation probably also contributed to the observe money benefit. Together, these findings suggest that LIPFC does play a causal role in episodic memory formation.
- Subjects
BRAIN mapping; MAGNETIC resonance imaging; PREFRONTAL cortex; BRAIN stimulation; BRAIN function localization; ELECTRONIC behavior control
- Publication
Journal of Cognitive Neuroscience, 2004, Vol 16, Issue 2, p178
- ISSN
0898-929X
- Publication type
Article
- DOI
10.1162/089892904322984490