Prefrontal Cortex Oxygenation Evoked by Convergence Load Under Conflicting Stimulus-to-Accommodation and Stimulus-to-Vergence Eye-Movements Measured by NIRS

Brain structural and functional magnetic resonance imaging alterations in individuals with convergence insufficiency

PURPOSE

Individuals with convergence insufficiency (CI) encounter challenges in turning their eyes inward during near work. It is unclear how this relates to brain structural and functional alterations. This study aimed to explore the neural mechanism underlying CI using multimodal brain magnetic resonance imaging (MRI).

METHODS

Thirty-four CI participants and 35 healthy controls (HC) were recruited, who underwent visual examinations and brain MRI scanning. Structural MRI data were analysed to calculate cortical thickness, volume and surface area. Fractional amplitude of low-frequency fluctuation (fALFF) and seed-based functional connectivity were obtained from resting-state functional MRI data. The brain structural and functional metrics were compared between the two groups followed by correlation analyses between clinical measurements and significant brain features.

RESULTS

Relative to HC, individuals with CI had lower grey matter volume (GMV) and surface area in the right frontal eye fields, parietal eye fields and left medial orbitofrontal cortex, higher GMV and surface area in the right middle frontal and inferior temporal gyri and higher fALFF of the left cerebellum and functional connection between bilateral cerebellums. GMV of the right middle frontal gyrus and fALFF in the left cerebellum were positively correlated with the near point of convergence in all participants.

CONCLUSIONS

Lower structural metrics in the visual and oculomotor cortices and higher functional activity in the cerebellum may underpin convergence dysfunction and visual fatigue, while higher structural metrics in the right middle frontal and inferior temporal gyri reflect partial compensation for the visual and oculomotor cortex defects, thereby maintaining attention and parallax information processing. This study may enhance understanding of the neural mechanism of CI by revealing the impact of abnormal visual experiences of CI on the brain with disassociated structural and functional alterations in the vergence system.

Decoding visual fatigue in a visual search task selectively manipulated via myopia-correcting lenses

Introduction

Visual fatigue resulting from sustained, high-workload visual activities can significantly impact task performance and general wellbeing. So far, however, little is known about the underlying brain networks of visual fatigue. This study aimed to identify such potential networks using a unique paradigm involving myopia-correcting lenses known to directly modulate subjectively-perceived fatigue levels.

Methods

A sample of N = 31 myopia participants [right eye-SE: -3.77D (SD: 2.46); left eye-SE: -3.75D (SD: 2.45)] performed a demanding visual search task with varying difficulty levels, both with and without the lenses, while undergoing fMRI scanning. There were a total of 20 trials, after each of which participants rated the perceived difficulty and their subjective visual fatigue level. We used representational similarity analysis to decode brain regions associated with fatigue and difficulty, analyzing their individual and joint decoding pattern.

Results and discussion

Behavioral results showed correlations between fatigue and difficulty ratings and above all a significant reduction in fatigue levels when wearing the lenses. Imaging results implicated the cuneus, lingual gyrus, middle occipital gyrus (MOG), and declive for joint fatigue and difficulty decoding. Parts of the lingual gyrus were able to selectively decode perceived difficulty. Importantly, a broader network of visual and higher-level association areas showed exclusive decodability of fatigue (culmen, middle temporal gyrus (MTG), parahippocampal gyrus, precentral gyrus, and precuneus). Our findings enhance our understanding of processing within the context of visual search, attention, and mental workload and for the first time demonstrate that it is possible to decode subjectively-perceived visual fatigue during a challenging task from imaging data. Furthermore, the study underscores the potential of myopia-correcting lenses in investigating and modulating fatigue.

Visual ergonomics, performance and the mediating role of eye discomfort: a structural equation modelling approach

The purpose of this study was to model the visual ergonomic factors affecting performance in human-computer interaction. A cross-sectional study using structural equation modelling was performed with a sample of 200 participants. The measuring instruments included the office lighting survey questionnaire, performance assessment questionnaires, visual ergonomics assessment and an eye discomfort assessment. The hypothetical model evaluated workplace lighting status and visual ergonomics as precursors, performance as the output and eye discomfort as a mediator. The results showed that eye discomfort directly affected performance. Visual ergonomics also had a significant direct effect on eye discomfort. The final model suggested a significant new path between the quality of lighting and visual ergonomics. Also, the quality of lighting had an indirect effect on eye discomfort and performance, and the effect of visual ergonomics on performance was the same. Improving the lighting quality and visual ergonomics can reduce eye discomfort and increase performance.

The Effects of a Single Session of a Rhythmic Movement Program on Selected Biopsychological Parameters in PD Patients: A Methodological Approach

The aim of the present study is to examine the acute effects of a specially designed musicokinetic (MSK) program for patients with Parkinson's disease (PD) on (a) anxiety levels, (b) select kinematic and kinetic parameters, and (c) frontal cortex hemodynamic responses, during gait initiation and steady-state walking. Methods: This is a blind cross-over randomized control trial (RCT) in which 13 volunteers with PD will attend a 45 min MSK program under the following conditions: (a) a synchronous learning format and (b) an asynchronous remote video-based format. Changes in gait biomechanics and frontal cortex hemodynamic responses will be examined using a 10-camera 3D motion analysis (Vicon T-series, Oxford, UK), and a functional near-infrared spectroscopy (f-NIRS-Portalite, Artinis NL) system, respectively, while anxiety levels will be evaluated using the Hamilton Anxiety Rating Scale. Expected results: Guided by the rules of music, where periodicity is distinct, our specially designed MSK program may eventually be beneficial in improving motor difficulties and, hence, reducing anxiety. The combined implementation of f-NIRS in parallel with 3D gait analysis has yet to be evaluated in Parkinsonian patients following a MSK intervention. It is expected that the aforementioned intervention, through better rhythmicity, may improve the automatization of motor control, gait kinematics, and kinetics-supported by decreased frontal cortex hemodynamic activity-which may be linked to reduced anxiety levels.