Poster B28, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
The angular gyrus is activated by episodic retrieval but deactivated by semantic retrieval
Gina Humphreys1, Matthew Lambon Ralph1;1The University of Cambridge
Introduction The inferior parietal lobe (IPL), particularly the angular gyrus (AG), forms a key component of the default mode network (DMN) i.e. a network that shows task-related deactivation relative to rest. A large meta-analysis of fMRI studies implicates overlapping IPL regions in numerous cognitive domains [1]. There are several alternative hypotheses regarding IPL’s underlying cognitive function: a) IPL is a semantic-hub storing multi-modal semantic information [2]. b) IPL stores/buffers episodic memory [3,4]. c) IPL, as part of the wider DMN, is involved when attention is internally-directed, such as when recalling semantic/episodic memories [5,6]. Hence, when attention is externally directed (e.g. during the performance of most experimental tasks), internally-directed thoughts are suspended thus leading to deactivation of the DMN. Methods Twenty-two participants completed an fMRI study in which we manipulated internally vs. externally directed attention, and episodic retrieval vs. semantic retrieval. There were four conditions, two involving internally directed attention (semantic retrieval or episodic retrieval) and two involving externally directed visual attention (real-world object decision, or scrambled pattern decision). Additionally, for the episodic retrieval task, the participants reported the vividness of their episodic memory on each trial. Results The results showed that the AG, as well as the majority of the DMN, showed a clear preference for episodic retrieval over all other tasks: during episodic retrieval the AG showed significantly positive activation relative to rest, whereas during semantic retrieval and real-world object decision the AG was significantly deactivated (the scrambled pattern decision did not differ from rest). Furthermore, AG activation was found to correlate positively with the self-reported vividness of the retrieved episodic memory, whereas for all other conditions activation was negatively correlated with task difficulty (i.e. greater deactivation for greater difficulty). Conclusions The AG, and indeed the DMN more generally, is actively engaged during episodic retrieval, and the level of engagement relates positively to the vividness of the memory. Contradicting the semantic hypothesis, the semantic retrieval task was found to deactivate the AG, with the level of deactivation related to task difficulty, as shown elsewhere [7]. There was also little evidence to implicate AG in internally- vs. externally-directed attention. We theorise that in this study the IPL acts as online buffer of episodic information that is stored elsewhere in the brain. References [1] Humphreys & Lambon Ralph (2015) Cereb Cortex. 25: 3547-3560. [2] Binder et al. (2009) Cereb Cortex 19:2767-2796. [3] Vilberg & Rugg (2008) Neuropsychologia 46:1787-1799. [4] Wagner et al. (2005) Trends in Cognitive Sciences 9:445-453. [5] Andrews-Hanna (2012) Neuroscientist 18:251-270. [6] Buckner et al. (2008). Ann N Y Acad Sci 1124:1-38. [7] Humphreys et al. (2015). PNAS 112: 7857–7862.
Themes: Meaning: Lexical Semantics, Meaning: Combinatorial Semantics
Method: Functional Imaging