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Neuroanatomical correlates of the near response: voluntary modulation of accommodation/vergence in the human visual system
Author(s) -
Richter Hans O.,
Lee Joel T.,
Pardo José V.
Publication year - 2000
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.2000.00962.x
Subject(s) - neuroscience , psychology , eye movement , fixation (population genetics) , saccadic masking , visual cortex , microsaccade , extrastriate cortex , accommodation , vergence (optics) , audiology , medicine , physics , optics , population , environmental health
This study identifies brain regions participating in the execution of eye movements for voluntary positive accommodation (VPA) during open‐loop vergence conditions. Neuronal activity was estimated by measurement of changes in regional cerebral blood flow (rCBF) with positron emission tomography and 15 O‐water. Thirteen naive volunteers viewed a checkerboard pattern with their dominant right eye, while a lens interrupted the line of gaze during alternate 1.5 s intervals. Three counterbalanced tasks required central fixation and viewing of a stationary checkerboard pattern: (i) through a 0.0 diopter (D) lens; (ii) through a −5.0‐D lens while avoiding volitional accommodation and permitting blur; and (iii) through a −5.0‐D lens while maintaining maximal focus. The latter required large‐amplitude, high‐frequency VPA. As an additional control, seven of the subjects viewed passively a digitally blurred checkerboard through a 0.0‐D lens as above. Optometric measurements confirmed normal visual acuity and ability to perform the focusing task (VPA). Large‐amplitude saccadic eye movements, verified absent by electro‐oculography, were inhibited by central fixation. Image averaging across subjects demonstrated multifocal changes in rCBF during VPA: striate and extrastriate visual cortices; superior temporal cortices; and cerebellar cortex and vermis. Decreases in rCBF occurred in the lateral intraparietal area, prefrontal and frontal and/or supplementary eye fields. Analysis of regions of interest in the visual cortex showed systematic and appropriate task dependence of rCBF. Activations may reflect sensorimotor processing along the reflex arc of the accommodation system, while deactivations may indicate inhibition of systems participating in visual search.