Biomedical Engineering Report Paper Example

Event-related EEG Power Modulations and Functional Connectivity Change during Visual Task between Individuals

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 (Ferri, Rundo, Bruni, Terzano & Stam, 2007). 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 (Millet, 2001). 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).

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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 (Yadava, Kumar, Saini, Roy & Dogra, 2017). 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).

The introduction of visual stimuli helps in affecting the brain activities. As each stimulus is introduced, the emotions of a person are changed, in turn activating the neural circuit of the brain as one response to either a positive or negative stimulus. However, the neutral stimulus tends to have balanced activities in the brain due to balanced tasks taking place in the brain. It should be noted that visual stimuli have the effects of enhancing the activities of the respective sensory cortical areas of the brain that are involved in the coordination of the cognitive resources like attention. 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. The research used three stimuli to determine the different brain activities based on the emotional mental tasks. The results were then analyzed through the construction of the brain matrices and topography to determine the extent of the connectivity and power of the brain when the three stimuli were introduced.

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 (Qin, Ibrahim, Zaid, Malin, Azmin & Azman, 2018; Teo, Hou, Tian & Mountstephens, 2018; Bashivan, Rish & Heisig, 2016). 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.

Similarly, Scheeringa, Petersson, Kleinschmidt, Jensen, and Bastiaansen (2012) conducted a research with the aim of determining assess whether fMRI-based connectivity and frequency-specific EEG power are related. The researchers decided to conduct the study following the previous trends in research over the last decade leading to 2012. The researcher notd that the fast and transient coupling and uncoupling of functionally related brain regions into networks has, over that decade, been heavily studied in the context of cognitive neuroscience. The researchers further noted that the empirical tools utilized in the study of network coupling included functional magnetic resonance imaging (fMRI)-based functional and/or effective connectivity, and electroencephalography (EEG)/magnetoencephalography-based measures of neuronal synchronization.

The authors utilized simultaneously recorded EEG and fMRI in their effort to asses the relationship between the fMRI-based connectivity and frequency-specific EEG power. As such, they collected data from participants in their resting state, whereby they studied the relationship that exists between posterior EEG alpha power fluctuations and connectivity within the visual network and between the visual cortex and the rest of the brain. Consequently, the results showed that when alpha power increased, BOLD connectivity between the primary visual cortex and occipital brain regions decreased and that the negative relation of the visual cortex with the anterior/medial thalamus decreased and the ventral-medial prefrontal cortex is reduced in strength. Similar results were recorded by the study conducted by Jirsa, Sporns, Breakspear, Deco, McIntosh (2010) and Protzner, Kovacevic, Cohn & McAndrews, (2013). These effects were specific for the alpha band, and not observed in other frequency bands. The decreased connectivity within the visual system may indicate an enhanced functional inhibition during a higher alpha activity. This higher inhibition level also attenuates long-range intrinsic functional antagonism between the visual cortex and the other thalamic and cortical regions. Together, these results illustrated that power fluctuations in posterior alpha oscillations result in local and long-range neural connectivity changes, just as Wang, McIntosh, Kovacevic, Karachalios and Protzner (2016) noted in their study.

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, which was similar to the methodology used by Friston (2011). 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, a similar result by Cocchi, Toepel, De Lucia, Martuzzi, Wood et al. (2011). 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 (Sigman & Dehaene, 2008). 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 (Zalesky, Fornito & Bullmore, 2010). 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 as suggested by (Zalesky, Fornito, Harding & Cocchi, 2010). 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. The results were then analyzed through the construction of the brain matrices and topography to determine the extent of the connectivity and power of the brain when the three stimuli were introduced.

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 transla...