Lying in a 3T MRI scanner induces neglect-like spatial attention bias

Abstract

The static magnetic field of MRI scanners can induce a magneto-hydrodynamic stimulation of the vestibular organ (MVS). In common fMRI settings, this MVS effect leads to a vestibular ocular reflex (VOR). We asked whether – beyond inducing a VOR – putting a healthy subject in a 3T MRI scanner would also alter goal-directed spatial behavior, as is known from other types of vestibular stimulation. We investigated 17 healthy volunteers, all of which exhibited a rightward VOR inside the MRI-scanner as compared to outside-MRI conditions. More importantly, when probing the distribution of overt spatial attention inside the MRI using a visual search task, subjects scanned a region of space that was significantly shifted toward the right. An additional estimate of subjective straight-ahead orientation likewise exhibited a rightward shift. Hence, putting subjects in a 3T MRI-scanner elicits MVS-induced horizontal biases of spatial orienting and exploration, which closely mimic that of stroke patients with spatial neglect.

Spatial neglect after stroke is reduced when lying inside a 3T MRI scanner

“…When exploring their surroundings for possible targets, subjects' eye movements are no longer symmetrically distributed in the horizontal dimension but biased towards the side of cold CVS. To summarize, the present results in a patient with spatial neglect as well as the previous observations in healthy subjects by Lindner et al (2021) demonstrate a close physiological correspondence of MVS and CVS. The two types of vestibular stimulation evoke very similar if not identical behavioral effects in healthy subjects as well as in stroke patients with spatial neglect.…”

“…The grey boxes reflect the 95% confidence interval [corrected] of the difference between the normal population mean and the patient’s score (SINGLIMS-test; respective p-values are provided as p S [corrected for multiple comparisons]). Additional p-values are provided for the paired t-test comparisons of changes in control subjects’ center of visual search across task phases (p T ; compare Lindner et al, 2021) as well as for the corresponding Wilcoxon rank sum tests in W.E. (p W ).…”

“…Under this condition, the center of healthy subjects’ visual scan-path during visual search deviated towards the right, as is also the case for most patients with spatial neglect (compare above). Lindner et al (2021) further observed that for an “inverted” positioning in the scanner, i.e., when subjects entered the scanner with their feet first, MVS led to inverted behavioral effects: healthy subjects now showed a bias to the left instead of to the right side. We thus asked whether the behavioral effects of MVS on spatial attention and orientation during “inverse positioning” could be used to reduce the pathological core symptoms of stroke patients with spatial neglect of the left side of space.…”

“…The statistical procedures to test for any MVS-effects on the behavior of our group of healthy control subjects have been described in detail before (Lindner et al, 2021). In order to probe for comparable MVS-induced effects on patient W.E.…”

Go with the flow

“…The mere presence within an MRI scanner environment may a ect perceptual decision making (Maanen et al, 2016) and cognitive control (Hommel et al, 2012). MRI scanning can cause vestibular stimulation (Roberts et al, 2011) which may lead to spatial attention biases (Lindner et al, 2021). The MRI environment may furthermore impact EEG (Assecondi et al, 2010) and eyetracking measures (Mack et al, 2021), and can in some cases lead to changed reaction times (Koch et al, 2003;Koten et al, 2013).…”