An enhanced role for right hV5/MT+ in the analysis of motion in the contra- and ipsi-lateral visual hemi-fields

Samantha L Strong,Edward H Silson,André D Gouws,Antony B Morland,Declan J Mckeefry

doi:10.1016/j.bbr.2019.112060

Abstract

Previous experiments have demonstrated that transcranial magnetic stimulation (TMS) of human V5/MT+, in either the left or right cerebral hemisphere, can induce deficits in visual motion perception in their respective contra- and ipsi-lateral visual hemi-fields. However, motion deficits in the ipsi-lateral hemi-field are greater when TMS is applied to V5/MT + in the right hemisphere relative to the left hemisphere. One possible explanation for this asymmetry might lie in differential stimulation of sub-divisions within V5/MT + across the two hemispheres. V5/MT + has two major sub-divisions; MT/TO-1 and MST/TO-2, the latter area contains neurons with large receptive fields (RFs) that extend up to 15° further into the ipsi-lateral hemi-field than the former. We wanted to examine whether applying TMS to MT/TO-1 and MST/TO-2 separately could explain the previously reported functional asymmetries for ipsi-lateral motion processing in V5/MT + across right and left cerebral hemispheres. MT/TO-1 and MST/TO-2 were identified in seven subjects using fMRI localisers. In psychophysical experiments subjects identified the translational direction (up/down) of coherently moving dots presented in either the left or right visual field whilst repetitive TMS (25 Hz; 70%) was applied synchronously with stimulus presentation. Application of TMS to MT/TO-1 and MST/TO-2 in the right hemisphere affected translational direction discrimination in both contra-lateral and ipsi-lateral visual fields. In contrast, deficits of motion perception following application of TMS to MT/TO-1 and MST/TO-2 in the left hemisphere were restricted to the contra-lateral visual field. This result suggests an enhanced role for the right hemisphere in processing translational motion across the full visual field.

Highlights

Asymmetries between the functional capabilities of the right and left cerebral hemispheres in the human brain have been reported for various aspects of sensory, motor and cognitive function such as language [1], attention [2], spatial processing [3], and face perception [4,5]
Pairwise comparisons showed that application of transcranial magnetic stimulation (TMS) to both middle temporal sub-division (MT)/TO-1 and MST/TO-2 produced significant reductions in the ability of subjects to determine the direction of motion of the dots relative to both baseline and control (LO-1) conditions in the contra-lateral hemi-field (MT/TO-1 versus baseline, p = 0.012; MST/TO-2 versus baseline, p = 0.003; MT/TO-1 versus control, p = 0.024; MST/TO-2 versus control, p = 0.009), and the ipsi-lateral hemi-field (MT/TO-1 versus baseline, p = 0.005; MST/TO-2 versus baseline, p = 0.010; MT/TO-1 versus control, p = 0.040; MST/TO-2 versus control, p = 0.004)
No other pairwise comparisons were found to be significant (p > 0.2 in all cases). This indicates that within the right hemisphere, both MT/TO-1 and MST/TO-2 are essential for the perception of translational motion across the whole visual field

Summary

Introduction

Asymmetries between the functional capabilities of the right and left cerebral hemispheres in the human brain have been reported for various aspects of sensory, motor and cognitive function such as language [1], attention [2], spatial processing [3], and face perception [4,5]. It is unclear whether functional lateralisation is a feature that underpins the analysis of moving objects in the visual environment. The posterior middle temporal sub-division (MT) appears to respond preferentially to 2D planar motion [26,27], whilst the more anterior dorsal middle superior temporal sub-division (MSTd) responds preferentially to visual features pertaining to optic flow e.g. radial, rotational, and spiral directional motion [28,29,30]

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