Abstract
Objective.
Leftward optokinetic stimulation (OKS) is a promising therapeutic
approach for right-hemisphere stroke patients with left hemispatial
neglect. We questioned whether the putative neural basis is an
activation of frontoparietal brain regions involved in the control of
eye movements and spatial attention.
Methods. We used functional
magnetic resonance imaging to investigate brain activations during OKS
in acute right-hemisphere stroke patients (RHS, n = 19) compared with
healthy control subjects (HC, n = 9). Based on neuropsychological
testing we determined the ipsilesional attention bias in all RHS
patients, 11 showed manifest hemispatial neglect.
Results. In HC
subjects, OKS in either direction led to bilateral activation of the
visual cortex (V1-V4), frontal (FEF) and supplementary (SEF) eye fields,
intraparietal sulcus (IPS), basal ganglia, and thalamus. RHS patients’
activations were generally reduced compared with HC. Nevertheless,
leftward OKS bilaterally activated the visual cortex (V1-V4), FEF, SEF,
IPS, and thalamus. The neural response to OKS was negatively correlated
with patients’ behavioral impairment: The greater the individual
attention bias/neglect the weaker the brain activations.
Conclusion.
In RHS patients, leftward OKS activates frontoparietal regions (FEF,
IPS) that are spared from structural brain damage and functionally
involved in both oculomotor control and spatial attention. This may
provide a neural basis for the known therapeutic effects of OKS on
hemispatial neglect. In acute stroke stages, reduced activation levels
correlating with neglect severity indicate functional downregulation of
the underlying dorsal attention network. Therefore, chronic RHS patients
with less severe neglect after recovery of network disturbances may be
more suitable candidates for OKS rehabilitation.
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