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

Anti-saccades predict cognitive functions in older adults and patients with Parkinson's disease

A major component of cognitive control is the ability to act flexibly in the environment by either behaving automatically or inhibiting an automatic behaviour. The interleaved pro/anti-saccade task measures cognitive control because the task relies on one's abilities to switch flexibly between pro and anti-saccades, and inhibit automatic saccades during anti-saccade trials. Decline in cognitive control occurs during aging or neurological illnesses such as Parkinson's disease (PD), and indicates decline in other cognitive abilities, such as memory. However, little is known about the relationship between cognitive control and other cognitive processes. Here we investigated whether anti-saccade performance can predict decision-making, visual memory, and pop-out and serial visual search performance. We tested 34 younger adults, 22 older adults, and 20 PD patients on four tasks: an interleaved pro/anti-saccade, a spatial visual memory, a decision-making and two types of visual search (pop-out and serial) tasks. Anti-saccade performance was a good predictor of decision-making and visual memory abilities for both older adults and PD patients, while it predicted visual search performance to a larger extent in PD patients. Our results thus demonstrate the suitability of the interleaved pro/anti-saccade task as a cognitive marker of cognitive control in aging and PD populations.

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.

Adaptation changes in dynamic postural control and contingent negative variation during repeated transient forward translation in the elderly

BACKGROUND

Adaptation changes in postural control and contingent negative variation (CNV) for the elderly were investigated during repeated forward floor translation.

METHODS

Fifteen healthy elderly persons, living in the suburban area of Kanazawa City, Japan, underwent backward postural disturbance by a forward-floor translation (S2) 2 s after an auditory warning signal (S1). A set with 20 trials was repeated until a negative peak of late CNV was recognized in the 600-ms period before S2, and the last set was defined as the final set. Electroencephalograms, center of foot pressure in the anteroposterior direction (CoPap), and electromyograms of postural muscles were analyzed.

RESULTS

CoPap displacement generated by the floor translation was significantly decreased until the twelfth trial in the first set, and mean CoPap displacement was smaller in the second and final sets than in the first set. The mean displacement was significantly smaller in the final set than the previous set. A late CNV with a negative peak was not recognized in the first and second sets. However, most subjects (13/15) showed a negative peak by the fourth set, when the late CNV started to increase negatively from about 1,000 ms after S1 and peaked at about 300 ms before S2. At about 160 ms before the CNV peak, the CoPap forward shift started. The increase in timing of the gastrocnemius activity related to the CoPap shift was significantly correlated with the CNV peak timing (r = 0.64). After S2, peak amplitudes of the anterior postural muscles were significantly decreased in the final set compared to the first set.

CONCLUSIONS

It was demonstrated that even for the elderly, with so many repetitions of postural disturbance, a late CNV with a negative peak was recognized, leading to accurate postural preparation. This suggests the improvement of frontal lobe function (e.g., anticipatory attention and motor preparation) in the elderly.

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.

The effects of neck flexion on cerebral potentials evoked by visual, auditory and somatosensory stimuli and focal brain blood flow in related sensory cortices

BACKGROUND

A flexed neck posture leads to non-specific activation of the brain. Sensory evoked cerebral potentials and focal brain blood flow have been used to evaluate the activation of the sensory cortex. We investigated the effects of a flexed neck posture on the cerebral potentials evoked by visual, auditory and somatosensory stimuli and focal brain blood flow in the related sensory cortices.

METHODS

Twelve healthy young adults received right visual hemi-field, binaural auditory and left median nerve stimuli while sitting with the neck in a resting and flexed (20° flexion) position. Sensory evoked potentials were recorded from the right occipital region, Cz in accordance with the international 10-20 system, and 2 cm posterior from C4, during visual, auditory and somatosensory stimulations. The oxidative-hemoglobin concentration was measured in the respective sensory cortex using near-infrared spectroscopy.

RESULTS

Latencies of the late component of all sensory evoked potentials significantly shortened, and the amplitude of auditory evoked potentials increased when the neck was in a flexed position. Oxidative-hemoglobin concentrations in the left and right visual cortices were higher during visual stimulation in the flexed neck position. The left visual cortex is responsible for receiving the visual information. In addition, oxidative-hemoglobin concentrations in the bilateral auditory cortex during auditory stimulation, and in the right somatosensory cortex during somatosensory stimulation, were higher in the flexed neck position.

CONCLUSIONS

Visual, auditory and somatosensory pathways were activated by neck flexion. The sensory cortices were selectively activated, reflecting the modalities in sensory projection to the cerebral cortex and inter-hemispheric connections.