Event-Related EEG Power Modulations and Functional Connectivity Change During Visual Task Between Individuals

Introduction

Electroencephalography (EEG) is one of the methods used in monitoring the types of activities that takes place in the brain (Mahmoud, Dufor, Merlet, Berrou & Wendling, 2014). However, it is challenging to analyze EEG-based analysis methods due to lack of ground-truth brain activity references. In this regard, researchers have adapted to use simulated EEG data as opposed to using the actual EEG recordings in studying the effects of the brain. EEG was first applied to humans in the 1920s. Since then, the technique has undergone increasing research and development towards its application, which has seen it being utilized in several industries such as clinical setups, neuroscience, cognitive science among other fields (Frey, Daniel, Castet, Hachet, & Lotte, 2016).

Is your time best spent reading someone else’s essay? Get a 100% original essay FROM A CERTIFIED WRITER!

Order now

The EEG technique is increasing in its application due to its ability to reflect the electrostatic fields occurring primarily as a result of the coetaneous actions of the activity of the variations in the membrane potential of the postsynaptic terminal of a chemical synapse at apical dendrites in the cortical surface of the brain. These synchronous activities are captured by the electrodes that are attached to a human's scalp. In this case, the EEG is used in measuring the specific subset of the activities taking place in the brain (Wendling, Ansari-Asl, Bartolomei & Senhadji, 2009). The ability to regulate particular brain activities enables researchers to find cognitive and affective correlates when running the EEG experiment. Consequently, the mental state of participants under study can effectively be evaluated after the recordings or during the record of the EEG experiment (Zander et al., 2017). Furthermore, EEG has been continuously utilized since it is relatively cheap compared to the other brain monitoring techniques (Krol, Andreessen, & Zander, 2018). In this case, the researchers conducted EEG on different individuals to determine the functional connectivity change during visual tasks.

Purpose of the Research

The primary objective of the study was to determine the functional connectivity change using three kinds of visual stimuli on different individuals.

Literature Review

EEG has been utilized in several scientific studies to estimate the cognitive abilities of different individuals. For instance, Lechinger, Tomasz, Blume, Pichler, Michitsch, Donis, Gruber and Schabus, (2016) conducted a research to estimate the cognitive abilities of patients who have suffered or still suffering from consciousness disorders using the own name paradigm. In their study, Lechinger et al. (2016) recorded the EEG for 24 healthy controls, eight patients who suffered from the Unresponsive Wakefulness Syndrome (UWS) and seven minimally conscious (MCS) patients.

The authors then analyzed the EEG concerning the aptitude and the phase modulations as well as connectivity. According to their results, theta, alpha and delta frequencies showed overall reactivity. In the same way, the researchers recorded ERS/ERD as well as phase locking between the trials and the electrodes). In this case, the controls filed higher EEG results than the patients. Similarly, their research showed that the phase locking between the trials as well as delta phase connectivity was had more top recordings for own names in the passive and targets in the active condition. However, in the different types of patients studied, it was difficult to identify clear stimulus-specific differences. The researchers then concluded that EEG signature of the existing own name paradigm revealed helped in revealing that the healthy participants were correctly following instructions, further proving the applicability of EEG in studying the functional connectivity of the brain.

In the same way, Szostakiwskyj, Willatt, Cortese and Protzner (2017) conducted a research in an attempt of examining the effects of maturity from the stage of being a child to the state of being an adult on the magnitude and spatial extent of the state-to-state transformation of the brain signal variability, and its relationship with the cognitive performance of a person in these different stages. The researchers analyzed the nature and extent of the changes that occur when the participants were resting and when they were engaged in the experiments. The researchers then calculated the variability using multi-scale entropy (MSE) and further conducted an examination of the spectral power density (SPD) from the EEG test conducted for children aged between eight and fourteen years as well as in adults aged between eighteen and thirty-three years.

Their results showed that improved levels of processing local information mark the process of maturing, and a decline in the long-range interactions with other neural populations. The results also showed that the changes in MSE in children is the same in magnitude. However, these changes in children tend to be more spatially as the children transition from the internally- to externally-driven brain states. Their results also showed that there exists an interplay between the changes brought about by the maturity stages and the changes brought about by the state-to-state changes in brain signal variability. Consequently, the interaction causes more significant influence on the level that brain processes the available information. In this case, the research showed that EEG is an effective way of studying the brain activities of individuals.

Also, Cocchi, Zalesky, Ulrike, Thomas, De-Lucia, Murray and Carter (2011) conducted a study to investigate the spatial, temporal, spectral as well as functional characteristics of the valuable brain connections that take part in executing unrelated visual perceptions concurrently to ensure that the memory tasks are performed. The researchers analyzed EEG data through the use of an approach driven by unique data, that helped to assess the source soundness at the entire-brain level. According to the results, the dual task performance led to the modulation of three brain connections in the band of beta and one in the group of gammas. The soundness of beta rose within two dorsofrontal-occipital connections when the participants were handling two or more tasks in comparison to the situation where the participants were handling one task. The results showed that when the participants were tried as they had lower working memories, the results were highly coherent. When the researchers analyzed the soundness as a function of time, their analysis showed that dorsofrontal-occipital beta-connections were vital for maintaining working memory, while the prefrontal-occipital beta-connection and the inferior frontal-occipitoparietal gamma-connection were critical in controlling the processing of visual images in a top-down manner. As such, their study further showed the applicability of EEG in studying the different functionality of the brain of individuals.

Materials and Methods

Participants

10 participants viewed 69 pictures which were arranged into three-set (negative (depressive), positive, and neutral) while EEG data was recorded. All subjects voluntarily participated, and they did through the signing of the informed written consent which was given to them before the start of the study. The procedures followed in the selection of the participants and conducting the actual experiment was authorized by the Committee in charge of Ethics of the Biomedical engineering department.

Procedure

The experiment on EEG (Electroencephalography) was run by using three kinds of visual stimuli. The experimental task was based on emotional, mental tasks. 10 participants viewed 69 pictures which are arranged into three-set (negative (depressive), positive, and neutral) while EEG data was recorded. The stimulus presentation was randomized across conditions. All the pictures were similar regarding their sizes and resolution. We experimented with four blocks of 138 trials. Each participant completed four sessions. During each run, every image was shown once and in random order. The inter-trial interval was 2s, and all the trials were null trials of which only a gray background was shown to the participants, and the fixation cross turned darker for 100 ms. Finally, participants verified that they had no background knowledge about the contents of the pictures and rating of the images were done.

Results

Frequencies

The alpha, beta, theta, delta and gamma frequencies were extracted using Wavelet Toolbox* in the following manner.

The three visual stimuli used were the three different images. In the four different sessions for the ten participants, the most outstanding frequencies were the alpha and beta frequencies. The alpha frequencies of the participants mainly ranged from 9-11 Hz. The alpha frequencies were primarily recorded during the inter-trial intervals of 2s. During this time, several participants closed their eyes to relax, hence leading to the recording of the alpha frequencies.

However, as each visual stimulus was introduced, the wavelet changed differently for the adults. When the negative images were presented, 8 of the participants recorded wavelets of 25-28 Hz, hence translating as the beta frequencies. However, as the pictures were being moved, the level of beta frequencies reduced. Two of the ten participants, however, recorded 4.9 Hz and 7.5Hz respectively, which is an abnormal frequency for the awake adults. The records were translated as theta frequencies. However, there was no record of frequencies lower than 4Hz, hence lack of the record of delta frequencies. Introduction of the positive images, however, resulted in higher records of beta frequencies since most of the participants were alert to the size and resolution of the photos.

Effects on the Frontal-Central, Central and Centro-Parietal Sites of the Brain

The three visual stimuli had a different impact on the various sections of the brains of the participants. The mean score of the effects on the different sites shows that the frontal-central site of the mind for the three visual stimuli were FC3 (0.256356), FCz (-1.74499) and FC4 (-1.95777). Similarly, the effects on the central part of the brain had average scores of C3 (-3.65736), Cz (-2.0652) and C4 (-1.41711). In the same way, the effects on the Centro-parietal site of the brain had mean scores of CP3 (-0.41166), CPz (-2.36744) and CP4 (-1.3735).

Discussion

The following can be used to categorize the different frequencies of the EEG experiment

As such, the first frequency is the alpha frequencies. The alpha frequencies are the EEG frequencies ranging between 8-12Hz. These frequencies are generally prominent in the occipital regions of normal, relaxed adults, whose eyes are closed. However, as the adults open their eyes, or as they become more aware, the alpha frequencies tend to reduce and disappear. Since the participants closed their eyes to relax during the inter-trial period, the alpha frequencies were higher.

Beta rhythm, on the other hands, has frequencies ranging from 12-30Hz. During the experiment, 8 participants had frequencies ranging from 25 to 28Hz. The negative images required the adults to concentrate keenly on identifying the size and the resolution. The high concentration led to the recording of the higher beta frequencies. The beta frequencies are mainly observed in the frontal and central regions of the adults. As the adults become more alert, the frequencies of beta increase. In this case, the positive image visual stimuli recorded a lower frequency level compared to the negative since the concentration of the adults in identifying the positive image is not as high as it is for detecting the negative image...