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Time-related activity in the prefrontal cortex evoked by convergence load under conflicting stimulus-to-accommodation and stimulus-to-vergence eye-movements measured by near-infrared spectroscopy: Brain at work
University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences, Occupational health science. University of Gävle, Centre for Musculoskeletal Research.
Division of Occupational and Environmental Medicine, Department of Public Health Sciences, Karolinska Institute.
School of Optometry, Karolinska Institutet, Stockholm, Sweden.
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2018 (English)In: Article in journal (Refereed) Submitted
Abstract [en]

Purpose: To extend our knowledge of the functional linkages between visual fatigue and regional cerebral prefrontal cortex (PFC) activity, we measured hemodynamic changes over the right dorsolateral prefrontal cortex (dlPFC) during convergence load under conflicting stimulus-to-accommodation and stimulus-to-vergence eye movements with and without concurrent mental load.

Methods: Twenty healthy participants with a median age of 28 years (range: 18–44 years) fixated upon a vertical bar presented separately to the left and right eyes, using polarized filters, during four counterbalanced 10-min periods: (i) no accommodation/vergence conflict (Control, Ctrl); (ii) added convergence load and accommodation/vergence conflict (Conv); (iii) added cognitive load only (Cog) and; (iv) a combination of added cognitive and convergence load and accommodation/vergence conflict (Cc). Viewing distance was 65 cm. Non-invasive measurements of hemodynamic activity over the dlPFC were quantified by functional near-infrared spectrometry (fNIRS). During the two-convergence load conditions, the horizontal disparity of the two bars varied dynamically from no disparity to a disparity set 20% below the individual threshold for diplopia. Cognitive load was induced by the n-back-2 test which required the subject to memorize and recall the changing colors of the horizontal bars. fNIRS data were averaged over 10-s windows centered at 0, 2, 4, 6, 8 and 10 min of each task, subtracted from a 20-s baseline window immediately preceding the visual task, and then represented as changes in oxygenated hemoglobin (∆HbO2), deoxygenated hemoglobin (∆HHb) and total hemoglobin (∆tHb).

Results: Linear mixed model analyses showed that hemodynamic changes were systematically influenced by time (p<0.001). The group-averaged time-related level of change across the viewing conditions did not differ when compared between one another (p>0.05). Larger convergence eye-movement responses under conflicting stimulus-to-accommodation, and stimulus-to-vergence over time, increased ∆HbO2 and ∆tHb only in condition Cc and after 8 min of task time (p<0.10 for min-6 and min-8: p<0.05 for min-10).

Discussion: Collectively, our data suggest that HbO2, HHb and tHb, recorded over the dlPFC with fNIRS, can be used to assay the degree to which supervisory oculomotor control processes are activated during visually deficient near work. 

Place, publisher, year, edition, pages
2018.
Keywords [en]
Attention fatigue, Accommodation, Compensatory effort, Convergence, disparity, Near Infrared Spectroscopy (NIRS), Time series analysis, Visual ergonomics.
National Category
Occupational Health and Environmental Health
Identifiers
URN: urn:nbn:se:hig:diva-25766OAI: oai:DiVA.org:hig-25766DiVA, id: diva2:1163808
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-1761Available from: 2017-12-08 Created: 2017-12-08 Last updated: 2018-03-22Bibliographically approved

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Richter, HansElcadi, Guilherme H.Marsh, John E.Zetterberg, Camilla

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CiteExportLink to record
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