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Andrew T Smith, Matthew B Wall, Kai V Thilo; Vestibular input to human MST but not MT. Journal of Vision 2009;9(8):679. doi: 10.1167/9.8.679.
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© ARVO (1962-2015); The Authors (2016-present)
In macaques, cortical area MST receives vestibular as well as visual input. The vestibular tuning of MST neurons can be either (i) congruent with their tuning for optic flow, suggesting combination of cues to specify self-motion more accurately, or (ii) opposite, perhaps allowing head motion to be discounted in order to facilitate detection of object motion. In contrast, it is thought that macaque MT does not have vestibular afferents.
We have examined whether human MT and MST have vestibular inputs by applying galvanic vestibular stimulation (GVS) in combination with fMRI. GVS involves passing a controlled current between two electrodes attached to the mastoid processes, to stimulate the cranial nerves that connect the vestibular organs to the brainstem. We applied a 1Hz sinusoidal alternating current of ±1 mA during conventional fMRI acquisition at 3Tesla. All participants reliably experienced vestibular sensations during stimulation intervals (roll and/or yaw that alternated in direction at 1Hz). Scanning was performed in total darkness and also while continuously observing a static visual scene. In separate scans, MT and MST were identified conventionally with unilateral visual motion stimulation, exploiting the fact that MST but not MT responds to ipsilateral visual stimuli.
During GVS, significant time-locked activation was seen in the MT+ complex. It occurred in darkness as well as during vision so cannot be attributed to image motion caused by cyclotorsional eye movements. In every case, it occurred only in the anterior portion of MT+ and the active region corresponded well to MST as defined visually. Activity was also seen in parieto-insular vestibular cortex (PIVC). Suppression was often seen in occipital cortex and in somatosensory cortex, consistent with known inhibitory interactions.
We conclude that human MST receives vestibular afferents but human MT does not. In addition, GVS provides an alternative localizer for MST.
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