Cognitive mechanisms and motor control during a saccadic eye movement task: evidence from quantitative electroencephalography

Prediction of behavioral performance by alpha-band phase synchronization in working memory

Working memory (WM) is a cognitive system with limited capacity that can temporarily store and process information. The purpose of this study was to investigate functional connectivity based on phase synchronization during WM and its relationship with the behavioral response. In this regard, we recorded EEG/Eye tracking data of seventeen healthy subjects while performing a memory-guided saccade (MGS) task with two different positions (near eccentricity and far eccentricity). We computed saccade error as memory performance and measured functional connectivity using Phase Locking Value (PLV) in the alpha frequency band (8-12 Hz). The results showed that PLV is negatively correlated with saccade error. Our finding indicated that during the maintenance period, PLV between the frontal and visual area in trials with low saccade error increased significantly compared to trials with high saccade error. Furthermore, we observed a significant difference between PLV for near and far conditions in the delay period. The results suggest that PLV in memory maintenance, in addition to predicting saccade error as behavioral performance, can be related to the coding of spatial information in WM.

Alpha oscillation during the performance of a new variant of working memory-guided saccade task: Evidence from behavioral and electroencephalographic analyses

Working memory (WM) can be considered as a limited-capacity system which is capable of saving information temporarily with the aim of processing. The aim of the present study was to establish whether eccentricity representation in WM could be decoded from eletroencephalography (EEG) alpha-band oscillation in parietal cortex during delay-period while performing memory-guided saccade (MGS) task. In this regard, we recorded EEG and Eye-tracking signals of 17 healthy volunteers in a variant version of MGS task. We designed the modified version of MGS task for the first time to investigate the effect of locating stimuli in two different positions, in a near (6°) eccentricity and far (12°) eccentricity on saccade error as a behavioral parameter. Another goal of study was to discern whether or not varying the stimuli loci can alter behavioral and eletroencephalographical data while performing the variant version of MGS task. Our findings demonstrate that saccade error for the near fixation condition is significantly smaller than the far from fixation condition. We observed an increase in alpha power in parietal lobe in near vs far conditions. In addition, the results indicate that the increase in alpha (8-12 Hz) power from fixation to memory was negatively correlated with saccade error. The novel approach of using simultaneous EEG/Eye-tracking recording in the modified MGS task provided both behavioral and electroencephalographic analyses for oscillatory activity during this new version of MGS task.

Gamma-Band Modulation and Coherence in the EEG by Involuntary Eye Movements in Patients in Unresponsive Wakefulness Syndrome

Gamma power and coherence in the electroencephalogram increase in healthy individuals in association with voluntary eye movements, saccades. Patients with unresponsive wakefulness syndrome show repetitive involuntary eye movements that are similar to saccades but progress at a much lower speed. In the present study, we explored the changes in gamma power and coherence related to these eye movements and investigated whether any relationship to the patients' clinical status could be found that would indicate first neurophysiological signs of recovery. To this end, we assessed the clinical status and registered classical scalp electroencephalography with 19 surface electrodes and electro-oculogram of 45 consecutive patients at admission and at 4 weekly intervals. Slow gamma activity (in the frequency range of 37-40 Hz) was analyzed before, during, and after eye movements (pre, -intra and post-eye movement) by means of "continuous wavelet transform." We graded recovery using clinical behavioral scales, taking into account the variables, age, gender, recovery (yes or no), as well as the patients diagnoses (traumatic brain injury, hypoxia, hemorrhage, infection). Statistical evaluation was performed using DataLab, R, and Kruskal-Wallis methods. Based on the clinical status, we distinguished between recovering and chronic groups of patients. In comparison with the chronic group, the recovering group showed significantly higher gamma power over the posterior electrodes and significant higher values of coherence in the gamma-band activity during the presaccadic period of eye movements. We suggest that our findings on the onset of involuntary eye movements in the recovering group of patients with unresponsive wakefulness syndrome indicates a first neurophysiological sign of favorable prognosis.

Changes in absolute theta power in bipolar patients during a saccadic attention task

The present study analyzed absolute theta power (ATP) in brain areas involved with attention in the three phase of BD while the patients performing a saccadic attention task. We hypothesized that patients in depression and mania states show a higher ATP compared to euthymic patients, since a higher ATP is indicative of attention deficit. We analyzed the frontal (F7, F3, Fz, F4 and F8) and central (C3, Cz and C4) areas. Thirty bipolar patients were enrolled in this study. The subjects performed a saccadic attention task while their brain activity pattern was recorded using quantitative electroencephalography (20 channels). Our results showed a main effect for group over C3, C4, Cz, F7, F4, F8 electrodes, and a main effect for moment over Cz, F7, F8 electrodes. These results indicate that both task and groups produce changes in theta activity in distinct cortical areas that participate in the organization of attention. Our results therefore demonstrate that, although it is well established in the literature that theta has a relevant role in the attention process, it is necessary to deepen the investigations to better understand the specifics of theta during visual processing tasks that have a demand for attention.