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Hemispheric Specialisation in the Parietal Cortex and its Effect on Memory and Attention

Gray, Oliver

[Thesis]. Manchester, UK: The University of Manchester; 2018.

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Abstract

Healthy individuals tend to preferentially allocate attention to the left visual field (the pseudoneglect effect). This tendency has been closely linked with hemispheric specialisation of the right frontoparietal attention network (FPA) (including the lateral parietal cortex (LPC)). However, evidence is presented here showing that engaging semantic processing (left hemisphere specialised) during object recognition induces a right visual field bias, a reversal of the pseudoneglect effect. Other factors have also previously been shown to modulate the pseudoneglect effect; e.g. target and observer proximity, and horizontal stimulus length. A forced perspective misperception mechanism that directly links these effects is introduced here for the first time. These findings provide important developments in our understanding of LPC processing in spatial attention allocation. Though LPC engagement has been widely observed in neuroimaging studies of episodic memory retrieval, the functional role it plays in memory has been the subject of intense debate. This is debate is first addressed through a detailed systematic review of inferior parietal lobule (IPL) activations observed in previous fMRI studies of episodic memory. More consistent engagement of the right hemisphere IPL was observed during perceptual memory experiences than during semantic/conceptual memory experiences. The left hemisphere IPL demonstrated the opposite effect. The debate is further addressed by an fMRI study investigating the neural bases of retrieval of detailed perceptual experiences without engaging semantic/conceptual memory processing. As predicted, memory-related processing produced right IPL activation, and deactivation in the left IPL. Finally, a previously unrecognised association between the hemispheric lateralisation of IPL processing in perceptual memory retrieval and a memory advantage for items encoded on the left side of space is presented. Critically, this advantage is independent of perceptual pseudoneglect effects. Significant correlations between memory tasks provide a mechanistic link between representational pseudoneglect and the hemispheric specialisation of memory retrieval processing. This body of research is discussed with reference to hemispheric specialisation and the functional organisation of the IPL and the LPC, in attention and memory.