Functional neuroanatomy of the human near/far response to blur cues: eye-lens accommodation/vergence to point targets varying in depth

Authors

  • Hans O. Richter,

    1. Department of Ophthalmology, Karolinska Institute, Huddinge, Sweden
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  • Patricia Costello,

    1. Cognitive Neuroimaging Unit, Psychiatry Service, Veterans Affairs Medical Center, Minneapolis, USA
    2. Division of Neuroscience Research, Department of Psychiatry, University of Minnesota, Minneapolis, USA
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  • Scott R. Sponheim,

    1. Division of Neuroscience Research, Department of Psychiatry, University of Minnesota, Minneapolis, USA
    2. Department of Psychology, University of Minnesota, Minneapolis, USA
    3. Psychology Service, Veterans Affairs Medical Center, Minneapolis, USA
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  • Joel T. Lee,

    1. Cognitive Neuroimaging Unit, Psychiatry Service, Veterans Affairs Medical Center, Minneapolis, USA
    2. Division of Neuroscience Research, Department of Psychiatry, University of Minnesota, Minneapolis, USA
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  • José V. Pardo

    1. Cognitive Neuroimaging Unit, Psychiatry Service, Veterans Affairs Medical Center, Minneapolis, USA
    2. Division of Neuroscience Research, Department of Psychiatry, University of Minnesota, Minneapolis, USA
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  • *

    Present address: University of Gävle, Department of Education and Psychology, SE-801 76 Gävle, Sweden

Dr Hans O. Richter, at *present address below.
E-mail: hrr@hig.se.

Abstract

The purpose of this study was to identify the networks involved in the regulation of visual accommodation/vergence by contrasting the cortical functions subservient to eye-lens accommodation with those evoked by foveal fixation. Neural activity was assessed in normal volunteers by changes in rCBF measured with PET. Thirteen right-handed subjects participated in three monocular tasks: (i) resting with eyes closed; (ii) sustained foveal fixation upon a LED at 1.2 m (0.83 D); and (iii) accommodating alternately on a near (24 cm, 4.16 D) vs. a far (3.0 m, 0.33 D) LED alternately illuminated in sequential 2 s epochs. The contrast between the conditions of near/far accommodation and of constant foveal fixation revealed activation in cerebellar hemispheres and vermis; middle and inferior temporal cortex (BA 20, 21, 37); striate cortex and associative visual areas (BA 17/18). Comparison of the condition of constant fixation with the condition of resting with closed eyes indicated activation of cerebellar hemispheres and vermis; visual cortices (BA 17/18); a right hemisphere dominant network encompassing prefrontal (BA 6, 9, 47), superior parietal (BA 7), and superior temporal (BA 40) cortices; and bilateral thalamus. The contrast between the conditions of near/far accommodation with closed-eye rest reflected an incremental summation of the activations found in the previous comparisons (i.e. activations associated with constant fixation). Neural circuits activated selectively during the near/far response to blur cues over those during constant visual fixation, occupy posterior structures that include occipital visual regions, cerebellar hemispheres and vermis, and temporal cortex.

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