Research
Analyzing the Electroencephalograms of the Occipital Lobes During Cognitive Tasks, and the Relationship Between the Right and Left Lobes
By: Elimelech Strassman, Noah Diner, Netanel Glaser, Ariel Greenberg, Shlomo Shaulian, Joshua Lando, and Yaniv Cohen
​Introduction
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An electroencephalogram (EEG) is a device that can measure the electrical activity of the brain. Small electrodes are attached to the scalp, and the activity of varying wavelengths are recorded. The first ever EEG was made and used in 1924 by Hans Berger when performing a neurosurgical operation on a 17 year old boy [1]. EEG’s are commonly used in the medical setting to diagnose neurological diseases, such as epilepsy, sleep disorders, and brain tumors [2]. EEG’s can also be used in the world or research to uncover information on the physiology of the brain and the neural networks.
The frequency and amplitude of the waves in an EEG can inform on the activity and processes of the neurons in specific regions. For a specific region to have waves with a higher frequency or amplitude during certain activities would suggest dominance of that region during those activities (e.g. the overall higher levels of activity in the left hemisphere of the brain during speech production, and especially in Broca’s area). Symmetricity in the brain waves of two different regions would imply that the anatomy and wiring of their neural circuits are identical. Asymmetricity would suggest that the circuits have differences in their anatomy, physiology, or in an aspect of their molecular makeup.
In 2015, Dr. Yaniv Cohen had performed research with EEG’s to analyze the activity of the olfactory lobe in rats [3]. The goal of the study was to understand how learning and memory would affect different regions of the olfactory lobe, and the relationship between the right and left lobes during the process. The overall results of the study showed that there was asymmetry in the right and left olfactory lobes, especially in the piriform cortex, during different stages of learning. The goal of the current study is to identify if those same features (and any others) would be found in the occipital lobes of humans.
The procedure would require several test subjects to an identical protocol, while being recorded by the EEG. The protocol is broken down into 5 phases: Baseline, Reading in the Middle Visual Field, Memory Recall of Reading in the Middle Visual Field, Reading in the Right and Left Visual Fields, and Recall of Reading in the Right and Left Visual Fields. Each phase is broken up into three 5 minute sections (with the exception of Phase 4, which has six sections): performing the task with both eyes open, with the right eye open, and with the left eye open. Having a reading phase will be valuable to the experiment as it has been shown that EEG waves in the occipital lobe are related to cerebral engagement in reading tasks [4].
The analysis will focus on the amplitude and frequency of alpha and beta waves, and their level of symmetricity in the right and left occipital lobes. These wavelengths, as opposed to gamma and delta (which are found in activity between different brain regions), are found when there is activity in local sensory regions. Multiple studies have shown the significance of beta waves for visual tasks in the occipital lobe. A 2013 study aiming to learn about how beta band activity is related to visual tasks and attention in elderly subjects found that beta waves in the occipital lobe were correlated with visual tasks across all ages [5]. Another study showed similar results, that increased visual attention was correlated with increased beta waves not just in the primary visual cortex and lateral geniculate nucleus, but also in higher visual areas the lateral posterior and pulvinar complex [6].
Although beta waves were the focus of the 2015 study, alpha waves have been found to have higher activity in the occipital lobe, and will likely be given more attention in the current study. In previous studies, alpha waves were found to be significant in the occipital lobe, and having a correlation to temporal resolution of perceptual vision [7]. The goal will be to observe which of the phases have symmetry and asymmetry, and how that information can help us understand the relative function of the right and left occipital lobes during those specific tasks.
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Objective
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Our hypothesis is that there will be a greater level of symmetry between the right and left occipital lobes in for both alpha and beta waves during tasks that don’t differentiate between the right and left field of vision. However, tasks in which only one field of vision is being used will be expected to have higher level of activity to the corresponding occipital lobe.
Study Design
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The study recruited 8 participants from the Yeshiva University male undergraduate population. A 19 channel EEG, using a 10-20 EEG cap, was utilized to measure full brain activity, with a focus on the right and left occipital regions. An depiction of the EEG cap is displayed in Figure 1 below. The EEG recorded with 500 samples/second per channel simultaneously at 24 bits of resolution. Additionally, filtration was used to view the Alpha waves at 8-13 Hertz, and the Beta waves at 13-30 Hertz. Three screens were positioned on a table facing the participant; they were positioned centrally, on the left, and on the right fields of vision of the participant for visual tasks.
Figure 1. EEG Map, Top View
​​As mentioned, the procedure was split up into five phases, most containing three subsections. The first stage was the Baseline measurements. During the Baseline phase, participants were seated comfortably in a quiet and well-lit room with an EEG fastened to their head. Baseline measurements were conducted with both eyes open for a duration of 5 minutes. Subsequently, baseline measurements were repeated with only the left eye open for 5 minutes, followed by the reverse scenario with the right eye open and the left eye closed for 5 minutes.
The second phase of the procedure was the Reading Task, Middle Visual Field. In this phase, participants were instructed to focus on a reading task (on paper) attached on a screen positioned centrally. Reading tasks in the first subsection were performed with both eyes open for 5 minutes. The task was repeated with the left eye open, and the right eye closed for 5 minutes, and then with the right eye open and the left eye closed for 5 minutes.
The third phase was the Recall of a Memory. Participants were instructed to recall and think about the content read during the reading task. This recall phase was conducted with both eyes open for 5 minutes. Subsequently, participants engaged in recall with only the right eye open for 5 minutes, followed by recall with only the left eye open for 5 minutes.
The fourth phase was the Reading Task - Left and Right Fields. In this phase, participants were instructed to perform a reading task displayed on screens positioned on the left and right (as two separate subsections). Reading tasks were conducted with both eyes open for 5 minutes for each screen. Additionally, reading tasks were repeated with only the left eye open for 5 minutes and then with only the right eye open for 5 minutes for each screen. This added up to a total of six subsections.
The final phase was the Recall of a Memory Based on Field Orientation. In this phase, participants were instructed to recall and think about the content read based on the previous viewing orientation. The first subsection of this recall phase was conducted with both eyes open for 5 minutes. The next two subsections repeated the first one, with only the left or right eye opened.
The data collected during each phase were subsequently analyzed using the LabScribe software and appropriate statistical methods to examine the effects on the occipital lobe of different visual conditions on reading tasks and memory recall. Fast Fourier Transform (FFT) analysis, temporal alignment analysis, and amplitudes measurement were manually conducted. During the analysis, alpha and beta waves were compared with the unfiltered channel in order to exclude any events that were likely due to noise. Events of only a specific range were considered for the count: spanning between 400 and 800 milliseconds, and containing an amplitude that was at least 3 times the baseline amplitude (as long as it was also above .01 millivolts). It was also preferable for the event to contain at least three peaks (with the middlemost peak being the highest). An example of a snippet of a LabScribe reading with the unfiltered, alpha and beta channels is displayed in Figure 2.
Figure 2. Representative EEG recordings. Top two channels: Continuous signals of left and right OC without filtration. Bottom: Alpha and Beta left and right OC activity following filtration.
Results​
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Figure 3 displays the results from the FFT analysis of the EEG recordings. The FFT analysis shows an increase in the beta band power in the left/right occipital lobes during their respective reading tasks and memory recall. It is significant to note that the left OC Beta percent of change was greater than the right OC Beta percent of change for both the reading and memory recall.
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Figure 3. FFT Analysis
​Table 1 displays the results from an EEG recording of one of the participants of the study. The analysis performed for this participant (so far) only includes the amount of events that occurred during the recordings; other data, such as amplitude of the events and symmetry will be collected at a later point.
Table 1. Amount of EEG Events for a Participant
Figure 7
Figures 4-8 are bar charts of the results described by Table 1, split up by the five phases of the experiment.
Figure 4. Number of events for baseline.
Figure 5. Number of events for middle field readings.
Figure 6. Number of events for middle field recall.
Figure 7. Number of events for left and right fields reading.
Figure 8. Number of events for recall based on field orientation.
​There are a few noteworthy points to make about the results for this participant. Firstly, Figure 4 interestingly shows that having left eye opened decreases the amount of events for both occipital lobes, and for both alpha and beta waves. Also noteworthy is that in Figure 5, while reading from the middle field using the left eye caused a small increase in the amount of events (over both lobes, and for both alpha and beta waves), reading from from the middle field using the right eye caused an even greater decrease for the right occipital lobe, but a sharp decrease in the left occipital lobe (both alpha and beta). Something noteworthy from Figure 6 is that (when both eyes were open) there were more events for middle field recall in the right occipital lobe. Additionally, while middle field recall had the greatest amount of beta wave events when the left eye was open, it had the most amount of alpha wave events when the left eye was open.
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Conclusion​
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It can generally be concluded from the experiment that visual processing requires fast, local and desynchronized Beta activity. Importantly, visual memory recall that lacks visual input and has identical conditions as the baseline shows significant high Beta activity (secondary peak: 20-22 Hz). This may indicate that the memory recall requires substantial intrinsic sensory processing. Additionally, we observed greater changes in the left OC compared to the right OC in the low and high Beta power. This suggests the existence of asymmetric plasticity mechanisms of left-right OC. Recently, we also have studied these circuits in correlation to other behavioral paradigms developed in the laboratory such as the Visual Empathy paradigm. A comparison between the two paradigms in relation to the oscillatory activity correlated with the behavioral performance will expand our understanding of sensory information processing vs. knowledge processing.
References
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