J Clin Neurol.  2006 Mar;2(1):12-28. 10.3988/jcn.2006.2.1.12.

Therapeutic Effects of Caloric Stimulation and Optokinetic Stimulation on Hemispatial Neglect

• Moon SY
• Lee BH
• Na DL

• KMID: 2287699
• DOI: http://doi.org/10.3988/jcn.2006.2.1.12

Abstract

Hemispatial neglect refers to a cognitive disorder in which patients with unilateral brain injury cannot recognize or respond to stimuli located in the contralesional hemispace. Hemispatial neglect in stroke patients is an important predictor for poor functional outcome. Therefore, there is a need for effective treatment for this condition. A number of interventions for hemispatial neglect have been proposed, although an approach resulting in persistent improvement is not available. Of these interventions, our review is focused on caloric stimulation and optokinetic stimulation. These lateralized or direction-specific stimulations of peripheral sensory systems can temporarily improve hemispatial neglect. According to recent functional MRI and PET studies, this improvement might result from the partial (re)activation of a distributed, multisensory vestibular network in the lesioned hemisphere, which is a part of a system that codes ego-centered space. However, much remain unknown regarding exact signal timing and directional selectivity of the network.

Keyword

Neglect; Caloric stimulation; Optokinetic stimulation; Vestibular cortex; Ego-centered space

MeSH Terms

Brain Injuries
Humans
Magnetic Resonance Imaging
Perceptual Disorders*
Stroke

Figure

• 

  Figure 1 An illustration of left hemispatial neglect in right hemisphere stroke (A) Line bisection, (B) Modified Albert's line cancellation, (C) Copying of modified ogeden picture.

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  Figure 2 (A) Pathway for vestibulo-ocular reflex by left cold caloric stimulation. Cold water irrigation on left ear causes tonic deviation of eyeball to the left and rapid corrective eye movements toward the right. Thick lines are excited pathways and dotted lines are inhibited ones. (B) Central connection of vestibular system. Note that the vestibular apparatus is connected ipsilaterally with the spinal cord and cerebellum. Projections in the medial longitudinal fasciculus are both crossed and uncrossed. The projection to the thalamus and cerebral cortex is incompletely understood. III, oculomotor nuclei; IV, trochlear nuclei; VI, abducens nuclei; VIII, vestibular nuclei.

• 

  Figure 3 (A) Areas activated during caloric stimulation (warm water at 44℃) in the right ear of the right-handed healthy volunteers and in the left ear of those left-handed (group analysis; n=12; P<0.001; 15O-labelled H2O bolus, positron emission tomography). Activations were located in the anterior and posterior insula, the STG, the inferior frontal gyrus, the post-central gyrus, the IPL and the anterior cingulum. Note that the activations were more pronounced in right-handers during irrigation of the right ear in the right hemisphere and in left-handers during irrigation of the left ear in the left hemisphere. This indicates dominance of the non-dominant hemisphere in the processing of vestibular information. (B) Lateral views of the surfaces of both hemispheres showing activated areas during caloric stimulation of the right or left ear in right-handers in the superior temporal cortex, TPJ, insular cortex and inferior frontal cortex. Compared with the activation pattern during caloric irrigation of the right ear, caloric irrigation of the left ear led to activations which were smaller in both hemispheres and more frequently located within the ipsilateral left hemisphere. These results represent dominance of the ipsilateral vestibular pathways.49

• 

  Figure 4 A hypothetical scheme for horizontal smooth pursuit. Primary visual cortex (V1) projects to the homologue of the middle temporal visual area (MT) that in humans lies at the temporal-occipital-parietal junction. MT projects to the homologue of the medial superior temporal visual area (MST) and also to the frontal eye field (FEF). MST also receives inputs from its contralateral counterpart. MST projects through the retrolenticular portion of the internal capsule and the posterior portion of the cerebral peduncle to the dorsolateral pontine nucleus (DLPN). The DLPN also receives inputs important for pursuit from the FEF; these inputs descend in the medial portion of the cerebral peduncle. The DLPN projects, mainly contralaterally, to the flocculus, paraflocculus, and ventral uvula of the cerebellum; projections also pass to the dorsal vermis. The flocculus projects to the ipsilateral vestibular nuclei (VN), which in turn project to the contralateral abducens nucleus. Dotted circles show structures on the opposite side.

• 

  Figure 5 (A) OKN during rightward (upper row) and leftward (lower row) small-field visual stimulation vs. rest condition (stationary screen) in a group of 15 healthy right-handed volunteers elicited very similar bilateral activations of the visual cortex, which merged into the adjacent occipitotemporal (motion-sensitive area MT/V5) and parietooccipital areas including the parietal eye field (PEF) along the intraparietal sulcus. Additional activations were located nearly symmetrically in the anterior insular region and the adjacent parts of the inferior frontal gyri (GFi) as well as in different ocular motor structures such as the prefrontal cortex (PFC, GFm=middle frontal gyrus), frontal (FEF), and supplementary eye fields (SEF). For illustrative purposes, voxels above a threshold of P≤0.005 uncorrected are shown. (B) OKN during rightward (upper row) and leftward (lower row) small-field visual stimulation in a group of 15 healthy right-handed volunteers caused deactivations in the posterior corpus callosum which partly merged into adjacent parts of the posterior cingulate gyrus and optic radiation. Additional bilateral deactivations were found in the parieto-insular vestibular cortex (PIVC) in the posterior insula, in the central sulcus region (best attributed to the somatosensory cortex), and in the frontal-most and medial part of the right middle frontal gyrus (BA 8, GFm). For illustrative purposes, voxels above a threshold of P≤0.005 uncorrected are shown.92

• 

  Figure 6 Exploratory scan paths of an exemplary patient with spatial neglect (left) and a healthy subject (right) while searching for a (non-existent) target in darkness with their heads fixed. The upper panel shows the patients' exploratory eye movements with no further stimulation; the lower panel is the result under left-sided vestibular stimulation (cold water irrigation). In the condition without stimulation, the neglect patient showed a bias of ocular exploration towards the right and neglect of the left, while symmetrical eye movements were observed under unilateral vestibular stimulation. The healthy subject showed exactly the opposite behavior, i.e. symmetrical search without stimulation and asymmetrical search under vestibular stimulation.84

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  Figure 7 (A) Stimuli consist of stationary line superimposed on OKS. (B) The stimuli were projected on a large screen by a beam projector.

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