Zusammenfassung
INTRODUCTION: The angular gyrus (AG) is consistently reported in
neuroimaging studies of episodic memory retrieval and is a
fundamental node within the default mode network (DMN). Its
specific contribution to episodic memory is debated, with some
suggesting it is important for the subjective experience of
episodic recollection, rather than retrieval of objective
episodic details. Across studies of episodic retrieval, the left
AG is recruited more reliably than the right. We explored
functional connectivity of the right and left AG with the DMN
during rest and retrieval to assess whether connectivity could
provide insight into the nature of this laterality effect.
METHODS: Using data from the publically available 1000
Functional Connectome Project, 8min of resting fMRI data from
180 healthy young adults were analysed. Whole-brain functional
connectivity at rest was measured using a seed-based Partial
Least Squares (seed-PLS) approach (McIntosh and Lobaugh, 2004)
with bilateral AG seeds. A subsequent analysis used 6-min of
rest and 6-min of unconstrained, silent retrieval of
autobiographical events from a new sample of 20 younger adults.
Analysis of this dataset took a more targeted approach to
functional connectivity analysis, consisting of univariate
pairwise correlations restricted to nodes of the DMN. RESULTS:
The seed-PLS analysis resulted in two Latent Variables that
together explained \~86\% of the shared cross-block covariance.
The first LV revealed a common network consistent with the DMN
and engaging the AG bilaterally, whereas the second LV revealed
a less robust, yet significant, laterality effect in
connectivity - the left AG was more strongly connected to the
DMN. Univariate analyses of the second sample again revealed
better connectivity between the left AG and the DMN at rest.
However, during retrieval the left AG was more strongly
connected than the right to non-medial temporal (MTL) nodes of
the DMN, and MTL nodes were more strongly connected to the right
AG. DISCUSSION: The multivariate analysis of resting
connectivity revealed that the left and right AG show similar
connectivity with the DMN. Only after accounting for this
commonality were we able to detect a left laterality effect in
DMN connectivity. Further probing with univariate connectivity
analyses during retrieval demonstrates that the left preference
we observe is restricted to the non-MTL regions of the DMN,
whereas the right AG shows significantly better connectivity
with the MTL. These data suggest bilateral involvement of the AG
during retrieval, despite the focus on the left AG in the
literature. Furthermore, the results suggest that the
contribution of the left AG to retrieval may be separable from
that of the MTL, consistent with a role for the left AG in the
subjective aspects of recollection in memory, whereas the MTL
and the right AG may contribute to objective recollection of
specific memory details.
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