Parietal activity in episodic retrieval measured by fMRI and MEG - PubMed (original) (raw)
Parietal activity in episodic retrieval measured by fMRI and MEG
Tyler M Seibert et al. Neuroimage. 2011.
Abstract
Understanding the functional role of the left lateral parietal cortex in episodic retrieval requires characterization of both spatial and temporal features of activity during memory tasks. In a recent study using magnetoencephalography (MEG), we described an early parietal response in a cued-recall task. This response began within 100 milliseconds (ms) of the retrieval cue and lasted less than 400 ms. Spatially, the effect reached significance in all three anatomically defined left lateral parietal subregions included in the study. Here we present a multimodal analysis of both hemodynamic and electrophysiologic responses in the same cued-recall paradigm. Functional MRI (fMRI) was used to more precisely reveal the portion of the parietal cortex with the greatest response. The MEG data set was then reanalyzed to show the early MEG time course of the region identified by fMRI. We found that the hemodynamic response is greatest within the intraparietal sulcus. Further, the MEG pattern in this region shows a strong response during the first 300 ms following the cue to retrieve. Finally, when individual-dipole MEG activity is analyzed for the left cortical surface over the early 300-millisecond time window, significant recall-related activity is limited to a relatively small portion of the left hemisphere that overlaps the region identified by fMRI in the intraparietal sulcus.
Copyright © 2010 Elsevier Inc. All rights reserved.
Figures
Figure 1
Pair-cued recall task. Subjects viewed each pair for 3 seconds during the study phase (repeated in random order three times). MEG or fMRI recordings were acquired during the test phase (timeline on bottom of figure). In classify trials subjects made a simple living/nonliving judgment on the presented item. In recall-classify trials subjects retrieved the absent associate and then made a living/nonliving judgment on the item in memory. In both conditions the test item was equally likely to appear on the left and right sides. A fixation cross and two black boxes were presented during the initial 250 ms of the trial. The cue period is enlarged only for display in the figure. Reproduced with permission from Seibert et al., 2010.
Figure 2
(A) Three anatomical ROIs in the left lateral posterior parietal cortex. (B) Group-level _t_-statistics for greater BOLD response in the recall-classify condition than in the classify condition. (C) Analogous _t_-statistics for MEG response, averaged over the period from 0–300 ms after onset of the retrieval cue. The lower image in each frame is a superior view of the left hemisphere, rotated 30 degrees to show the intraparietal sulcus. Thresholds were set for _t_-statistics corresponding to controlling the false discovery rate over the left hemisphere at 0.05 (minimum) and 0.01 (maximum).
Figure 3
(A) Functional ROI defined from _t_-statistic map for greater BOLD activity in the recall-classify than in the classify condition. The lower image is a superior view of the left hemisphere, rotated 30 degrees to show the intraparietal sulcus. (B) Derived hemodynamic response functions (and standard error) for both conditions within the functional ROI. (C) Estimated MEG activity time series. “dSPM” refers to dynamic statistical parametric mapping, the MEG source localization method used. Recall-classify MEG activity was significantly greater than classify activity for the 100 ms time periods indicated in yellow (**: p < 0.001, ***: p < 10−5, ****: p < 10−7).
References
- Baddeley A. The episodic buffer: a new component of working memory? Trends Cogn Sci (Regul Ed) 2000;4(11):417–423. -PubMed
- Ciaramelli E, Grady CL, Moscovitch M. Top-down and bottom-up attention to memory: a hypothesis (AtoM) on the role of the posterior parietal cortex in memory retrieval. Neuropsychologia. 2008;46(7):1828–51. -PubMed
MeSH terms
LinkOut - more resources
Full Text Sources