Age-related reduction of hemispheric lateralisation for spatial attention: An EEG study

Gemma Learmonth,Christopher S.Y Benwell,Gregor Thut,Monika Harvey

doi:10.1016/j.neuroimage.2017.03.050

Abstract

A group-level visuospatial attention bias towards the left side of space (pseudoneglect) is consistently observed in young adults, which is likely to be a consequence of right parieto-occipital dominance for spatial attention. Conversely, healthy older adults demonstrate a rightward shift of this behavioural bias, hinting that an age-related reduction of lateralised neural activity may occur within visuospatial attention networks. We compared young (aged 18–25) and older (aged 60–80) adults on a computerised line bisection (landmark) task whilst recording event-related potentials (ERPs). Full-scalp cluster mass permutation tests identified a larger right parieto-occipital response for long lines compared to short in young adults (confirming Benwell et al., 2014a) which was not present in the older group. To specifically investigate age-related differences in hemispheric lateralisation, cluster mass permutation tests were then performed on a lateralised EEG dataset (RH-LH electrodes). A period of right lateralisation was identified in response to long lines in young adults, which was not present for short lines. No lateralised clusters were present for either long or short lines in older adults. Additionally, a reduced P300 component amplitude was observed for older adults relative to young. We therefore report here, for the first time, an age-related and stimulus-driven reduction of right hemispheric control of spatial attention in older adults. Future studies will need to determine whether this is representative of the normal aging process or an early indicator of neurodegeneration.

Highlights

Young adults tend to systematically overestimate the size, luminance, number and spatial frequency of objects within the left side of space relative to the right (‘pseudoneglect’) (Bowers and Heilman, 1980)
One-sample t-tests on the point of subjective equality (PSE) values for each block highlighted a significant, but transient, spatial bias in young adults towards the left side of space for long lines at the beginning of the experiment [Block 1: t(18)= -2.48, p=0.023], that is consistent with pseudoneglect
We present evidence of a stimulus- dependent, asymmetric engagement of the right hemisphere in young adults, accompanied by a baseline leftward spatial bias for long lines that is representative of pseudoneglect

Summary

Introduction

Young adults tend to systematically overestimate the size, luminance, number and spatial frequency of objects within the left side of space relative to the right (‘pseudoneglect’) (Bowers and Heilman, 1980). This leftward attention bias likely arises as a result of a right posterior-parietal dominance for visuospatial processing in young adults which results in a net asymmetry of activity between the right (RH) and left (LH) parietal cortices when performing spatial judgements. We have recently reported an increased right central parietal negativity for the landmark task vs a control in a window of 231–500 ms, with a peak bisection effect at 280 ms (Benwell et al, 2014a).

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