stimuli restricted to elbow rotation; such neurons appear to be related to joint movement per se, independent of direction. 7. Differences between area 6 and area 4 cells related to elbow movements were barely significant. During active movements, average onset times of cells in areas 6 and 4 were essentially the same. A slightly larger proportion of area 6 cells responded to passive rotation of multiple joints, and during controlled elbow movements they more often exhibited complex response patterns. 8. These results, in conjunction with lesion and stimulation studies, are consistent with a sensory as well as motor role for precentral cortex neurons. Under passive conditions, the responses evoked by joint rotation and cutaneous stimulation may be utilized in perception of such stimuli, particularly in the absence of the more sensitive postcentral cells.
Do mental images occur in a spatially mapped (i.e., analog, or array-format) representational medium? Kosslyn's (1978) method was used to measure the visual angle of "the mind's eye" to estimate the extent of the imagery medium before and after unilateral occipital lobectomy. It was found that the overall size of the largest possible image was reduced following the surgery. In addition, only the horizontal extent, and not the vertical extent, of the imagery medium was reduced. Finally, it was determined that the S understood the tasks, was not aware of our predictions, and was unaffected by a strong demand characteristic in a different imagery task. These results are consistent with the hypothesis that imagery occurs in a spatially mapped representational medium dependent on occipital cortex.
Migraine-related dizziness (MRD) refers to a disorder in which vestibular symptoms are an integral part of migraine symptomatology. The purpose of this study was to better define the pathophysiology of MRD, which is incompletely understood and to generate hypotheses regarding MRD by assessing the semicircular canal-ocular reflex, the otolith-ocular reflex, visual-vestibular interaction, vestibulo-spinal function, and visually induced postural sway. Subjects included five subjects with MRD, five subjects with migraine without dizziness, and five headache-free controls. Subjects with migraine were tested interictally. Results indicated that the mean gain of the semicircular canal-ocular reflex during both sinusoidal and constant velocity rotation was reduced in subjects with MRD. No changes were noted in the dynamics of the semicircular canal-ocular reflex. The otolith-ocular reflex, assessed with constant velocity OVAR, indicated that subjects with MRD showed a larger modulation component. No group differences were found in the bias component during constant velocity OVAR, nor in semicircular canal-otolith interaction or visual-vestibular interaction. Computerized dynamic posturography indicated that subjects with MRD demonstrated a surface-dependent pattern. Postural sway during optic flow indicated that subjects with MRD swayed more than the other subjects. We hypothesize that competing processes of serotonergic excitation and inhibition alter central vestibular pathways differently for semicircular canal vs. otolithic responses and for vestibulo-ocular vs. vestibulo-spinal pathways.
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