Effect of Vibration Stimulation to Neck Extensor Muscles on Reaction Time in Various Saccadic Eye Movements

Classification of short and long term mild traumatic brain injury using computerized eye tracking

Accurate, and objective diagnosis of brain injury remains challenging. This study evaluated useability and reliability of computerized eye-tracker assessments (CEAs) designed to assess oculomotor function, visual attention/processing, and selective attention in recent mild traumatic brain injury (mTBI), persistent post-concussion syndrome (PPCS), and controls. Tests included egocentric localisation, fixation-stability, smooth-pursuit, saccades, Stroop, and the vestibulo-ocular reflex (VOR). Thirty-five healthy adults performed the CEA battery twice to assess useability and test-retest reliability. In separate experiments, CEA data from 55 healthy, 20 mTBI, and 40 PPCS adults were used to train a machine learning model to categorize participants into control, mTBI, or PPCS classes. Intraclass correlation coefficients demonstrated moderate (ICC > .50) to excellent (ICC > .98) reliability (p < .05) and satisfactory CEA compliance. Machine learning modelling categorizing participants into groups of control, mTBI, and PPCS performed reasonably (balanced accuracy control: 0.83, mTBI: 0.66, and PPCS: 0.76, AUC-ROC: 0.82). Key outcomes were the VOR (gaze stability), fixation (vertical error), and pursuit (total error, vertical gain, and number of saccades). The CEA battery was reliable and able to differentiate healthy, mTBI, and PPCS patients reasonably well. While promising, the diagnostic model accuracy should be improved with a larger training dataset before use in clinical environments.

Trunk rotation and handedness modulate cortical activation in neglect-associated regions during temporal order judgments

The rotation of the trunk around its vertical midline could be shown to bias visuospatial temporal judgments towards targets in the hemifield ipsilateral to the trunk orientation and to improve visuospatial performance in patients with visual neglect. However, the underlying brain mechanisms are not well understood. Therefore, the goal of the present study was to investigate the neural effects associated with egocentric midplane shifts under consideration of individual handedness. We employed a visuospatial temporal order judgment (TOJ) task in healthy right- and left-handed subjects while their trunk rotation was varied. Participants responded by a saccade towards the stimulus perceived first out of two stimuli presented with different stimulus onset asynchronies (SOA). Apart from gaze behavior, BOLD-fMRI responses were measured using functional magnetic resonance imaging (fMRI). Based on findings from spatial neglect research, analyses of fMRI-BOLD responses were focused on a bilateral fronto-temporo-parietal network comprising Brodmann areas 22, 39, 40, and 44, as well as the basal ganglia core nuclei (caudate, putamen, pallidum).

We observed an acceleration of saccadic speed towards stimuli ipsilateral to the trunk orientation modulated by individual handedness. Left-handed participants showed the strongest behavioral and neural effects, suggesting greater susceptibility to manipulations of trunk orientation. With respect to the dominant hand, a rotation around the vertical trunk midline modulated the activation of an ipsilateral network comprising fronto-temporo-parietal regions and the putamen with the strongest effects for saccades towards the hemifield opposite to the dominant hand. Within the investigated network, the temporo-parietal junction (TPJ) appears to serve as a region integrating sensory, motor, and trunk position information.

Our results are discussed in the context of gain modulatory and laterality effects.

We examined the effect of trunk rotation on brain responses in neglect-associated areas.•

Trunk-related BOLD-fMRI activation patterns depend on handedness.

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They were modulated most during trunk rotation contralateral to the dominant hand.

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Trunk rotation and saccade direction show interaction effects at TPJ.

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TPJ serves as a region integrating sensory, motor, and trunk position information.

Developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion position

Background

We investigated developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion.

Methods

Subjects comprised 135 children (3–14 years) and 29 young adults (19–23 years). Children were divided into six groups in 2-year age strata. Pro-saccade reaction tasks for 30 s were performed in neck rest and flexion positions. Reaction times under each position were averaged in every 10-s period.

Results

Under neck rest position, reaction time in the 0–10 s period was significantly longer in the 3- to 4-year-old group than in the 5- to 6-year-old group and above. No significant age effect was found for reaction time in the 0–10 s period in the 5- to 6-year-old group and above. Although a significant effect of neck flexion was not observed until the 9- to 10-year-old group, significant shortening of reaction time with neck flexion was found in the 11- to 12-year-old group and above. Furthermore, this shortening was maintained until the first 20–s period in the 11- to 12-year-old group and during the entire 30 s in the 13- to 14-year-old and above.

Conclusions

These results suggest that brain activation with the maintenance of neck flexion, related to shortening of the pro-saccade reaction time, was found from a later age of approximately 11 years and above, compared with the age at which information-processing function in the pro-saccade was enhanced. In addition, brain activation with the maintenance of neck flexion was sustained longer with age.

Trunk rotation affects temporal order judgments with direct saccades: Influence of handedness

Manipulation of the trunk midline has been shown to improve visuospatial performance in patients with unilateral visual neglect. The goal of the present study was to disentangle motor and perceptual components of egocentric midline manipulations and to investigate the contribution of individual hand preference. Two versions of visual temporal order judgment (TOJ) tasks were tested in healthy right- and left-handed subjects while trunk rotation was varied. In the congruent version, subjects were required to execute a saccade to the first of two horizontal stimuli presented with different stimulus onset asynchronies (SOA). In the incongruent version, subjects were required to perform a vertical saccade to a pre-learned color target, thereby dissociating motor response from the perceptual stimulus location. The main findings of this study are a trunk rotation and response direction specific impact on temporal judgments in form of a prior entry bias for right hemifield stimuli during rightward trunk rotation, but only in the congruent task. This trunk rotation-induced spatial bias was most pronounced in left-handed participants but had the same sign in the right-handed group. Results suggest that egocentric midline shifts in healthy subjects induce a spatially-specific motor, but not a perceptual, bias and underline the importance of taking individual differences in functional laterality such as handedness and mode of perceptual report into account when evaluating effects of trunk rotation in either healthy subjects or neurological patients.

Effect of maintaining neck flexion on anti-saccade reaction time: an investigation using transcranial magnetic stimulation to the frontal oculomotor field

Background

Reaction time for anti-saccade, in which the gaze is directed to the position opposite to an illuminated target, shortens during maintenance of neck flexion. The present study applied transcranial magnetic stimulation (TMS) to the frontal oculomotor field, and investigated the effect of maintaining neck flexion on information processing time in the anti-saccade neural pathway before the frontal oculomotor field.

Methods

The reaction time was measured with the chin resting on a stand (‘chin-on’ condition) and with voluntary maintenance of neck flexion (‘chin-off’ condition) at 80% maximal neck flexion angle, with and without TMS. The TMS timing producing the longest prolongation of the reaction time was first roughly identified for 10 ms intervals from 0 to 180 ms after the target presentation. Thereafter, TMS timing was set finely at 2 ms intervals from −20 to +20 ms of the 10 ms step that produced the longest prolongation.

Results

The reaction time without TMS was significantly shorter (21.9 ms) for the chin-off (235.9 ± 14.9 ms) than for the chin-on (257.5 ± 17.1 ms) condition. Furthermore, TMS timing producing maximal prolongation of the reaction time was significantly earlier (18.6 ms) for the chin-off than the chin-on condition. The ratio of the forward shift in TMS timing relative to the reduction in reaction time was 87.8%.

Conclusions

We confirmed that information processing time in the anti-saccade neural pathway before the frontal oculomotor field shortened while neck flexion was maintained, and that this reduction time accounted for approximately 88% of the shortening of reaction time.

Effects of neck flexion on discriminative and cognitive processing in anticipatory postural control during bilateral arm movement

We investigated the effect of neck flexion on discriminative and cognitive processing in postural control during bilateral arm movement while standing, using event-related potential (ERP) and electromyogram. Fourteen healthy subjects flexed their arms to the target stimuli with a 20% probability in neck resting and flexion positions. Amplitude and latency of N2 and P3, anterior deltoid (AD) reaction time, onset time of postural muscles with respect to AD activation, and peak amplitude and latency of all muscles were measured. With neck flexion, N2 and P3 amplitudes increased, N2 and P3 latencies and AD reaction time shortened, and onset times of all postural muscles became earlier. No significant differences in peak amplitude and latency of each muscle were found between neck positions. Significant positive correlations were found in changes with neck flexion between P3 latency and AD reaction time, and between N2 latency and onset time of erector spinae. These suggest that with neck flexion, attention allocation to discriminative and cognitive processing increased, and the processing speed increased with shortening of reaction time in focal muscles. In addition, the onset time of postural muscles became earlier without changing the activation pattern, which was associated with the hastened discriminative processing.

Effects of anti-saccade training with neck flexion on eye movement performance, presaccadic potentials and prefrontal hemodynamics in the elderly

Anti-saccade performance, with strong contributions from frontal brain regions, reportedly deteriorates with age and maintenance of neck flexion and is known to cause brain activation. We investigated the effects of anti-saccade training on eye movement performance and frontal activity, and synergistic effects of training with neck flexion in the elderly. Thirty elderly individuals were divided into three equal groups: training group at neck resting position (NRT); training group at 20° neck flexion position (NFT); and untrained group. NRT and NFT performed approximately 200 anti-saccades (a block of 10-12 anti-saccades for 30 s × 20 blocks) per day over 3 weeks. Before and after training, horizontal eye movement, presaccadic potentials, and oxygenated hemoglobin concentration (oxy-Hb) in the prefrontal cortex during anti-saccades were tested in neck resting and 20° neck flexion conditions. In NRT and NFT, reaction time (-50 ms), percentage of erroneous saccades (-24%), and period between peak of presaccadic negativity and onset of spike potential (-16 ms) were significantly decreased through training. Only in NFT, after training, slight shortening of reaction time associated with neck flexion was recognized (-10 ms), and peak amplitude of presaccadic negativity was increased in both test neck conditions. Oxy-Hb was not significantly affected by trainings and test neck conditions. We demonstrated that in the elderly, anti-saccade training with both neck postures improved performance and facilitated related neural pathways. Moreover, training with neck flexion showed small but synergistic effects on performance and frontal activity. However, these trainings would be insufficient for elderly individuals to automatically control anti-saccade.

Neck-shortening effect on prosaccade reaction time formed through saccadic training accompanied by maintenance of neck flexion

We investigated the effect of neck-shortening on prosaccade reaction time formed through saccadic training accompanied by maintenance of neck flexion. The subjects were 30 university students who exhibited no significant shortening of prosaccade reaction time during maintenance of neck flexion, assigned to three groups: prosaccade training subjects at rest neck position (rest training group); prosaccade training subjects at 20 degrees neck flexion position (neck training group); and untrained subjects (control group). Saccadic training for 1 min was performed ten times per day, and the training period was 14 days. For the control group, no significant postural or training effects on reaction time were found. For both training groups, reaction time at the rest position after training was significantly shorter than that before training. For the neck training group, reaction time after training was significantly shorter at the neck flexion position than at the rest position. Conversely, no significant neck effect was found for the rest training group. This indicates that the shortening effect associated with maintenance of neck flexion on prosaccade reaction time is formed through saccadic training accompanied by maintenance of neck flexion.