Functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) are both measures used to examine the activities of the human brain. The first uses the magnetic field to detect magnetic change in the blood and the second uses electrodes placed on the human skull to detect electrical potentials. The main advantages and disadvantages of these two measures come in what they measure, their temporal resolution, their spatial resolution, and the strength of their data. Comment by Emma Soneson: This is a good introductory paragraph: I can tell that you've followed the "funnel" structure we talked about and created a thesis sentence that summarizes what you'll write about in the essay. Well done. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Functional magnetic resonance imaging (fMRI) measures hemodynamic changes after increased neural activity. “fMRI requires an MRI scanner, a high image acquisition speed, and specialized pulse sequences to measure localized brain activity.” (Voos& Pelphrey, 2013, p.2) This describes the basic settings for the operation of a functional MRI, which includes an MRI scanner to detect the contrast of deoxyhemoglobin in the blood, rapid acquisition of the images produced, and programs called scanning sequences pulses to send instructions to the scanner hardware to “turn certain hardware on or off at certain times” (Huettel, Song & McCarthy, 2009, p.42). Currently, the most common fMRI technique is the BOLD (Bold Oxygenation Level Dependent) technique, which uses magnetic resonance imaging to detect the direction of blood flow through changing oxygen content in the blood. Ogawa, Lee, Nayak, and Glynn (1990) first discovered the intrinsic BOLD contrast mechanism. To describe the mechanism in general, when a brain region is active, neurons in that region will communicate information with each other through electrical impulses: synaptic potentials and action potentials. This activity requires energy, which is provided by glucose and oxygen. As a result, elevated levels of oxyhemoglobin occur in the active areas, resulting in an increase in the surrounding ratio of oxyhemoglobin to deoxyhemoglobin. To meet energy and oxygen demands, oxygenated blood floods into the area and replaces deoxygenated blood (Ogawa, Lee, Nayak, & Glynn, 1990). The principle of MRI is that when people lie in an MRI scanner, the protons in people's bodies tend to align with the magnetic field (Huettel, Song & McCarthy, 2009). These protons then rotate around the field axis (Huettel, Song & McCarthy, 2009). In oxygenated blood, protons are organized and rotate at the same speed (Bekinschtein, 2019). In contrast, the protons in deoxygenated blood are not as organized, because deoxygenated hemoglobin molecules have magnetic field gradients that alter the spin rate of the nearby diffusing hydrogen nucleus. The local magnetic field is then influenced, and the change in the magnetic field can be detected by the long sequences of TE (time to echo) gradient echo pulses used in fMRI. Therefore the direction of oxygenated blood flow can be detected by MRI scanners through the difference in MR signals produced by oxygenated and deoxygenated blood. Comment by Emma Soneson: Since you clearly explain the quote in the previous sentence here, it is not necessary to include both Comment by Emma Soneson: Good understanding Comment by Emma Soneson: Almost word for word. Electroencephalography (EEG) is a non-invasive methodto detect the brain's neural activities by measuring the brain's electrical fields. Electrodes placed on the human scalp record voltage potentials, which result from current flow “in and around neurons” (Biasiucci, Franceschiello & Murray, 2019, p. R80). The main potential EEG measures are the electrical activities associated with post-synaptic dendritic currents generated in cortical pyramidal cells. This neural activity is called 'primary current' (Denes Szucs, handouts). “An excitatory postsynaptic potential in an apical dendrite will locally result in an intracellular current source. In the soma there will be an intracellular current sink and an extracellular current source. These source-sink configurations are also known as current dipoles” (Biasiucci, Franceschiello & Murray, 2019, p. R80). Brain tissue, CSF, and skull serve as a conductive medium for the propagation of electrical waves. This electrical activity that propagates is called “secondary current” (Denes Szucs, handouts). This current is also picked up by EEG electrodes placed on the human scalp. EEG can detect only a fraction of all the varieties of electrical activity occurring in the brain. However, the detected electrical signals can include physiological electrical activity, “such as cardiac, eye, and other muscle activity,” and environmental noise, “such as computer screens and other electrical equipment, power lines.” (Biasiucci, Franceschiello & Murray, 2019, p. R80). After describing two methods separately, we will compare their weaknesses and strengths. A disadvantage of fMRI is that “the BOLD signal cannot provide information regarding the directions of information flow.” (Voos& Pelphrey, 2013, p.3) That is, fMRI cannot identify the exact sequential neural activities in the process of information transmission, since BOLD is a neurometabolic signal and has a time delay compared to neural activities. Also due to the time delay, the temporal resolution of fMRI is coarse, on the order of seconds. (Shah, Anderson, Lee & WigginsIII, 2010) In contrast, EEG directly measures neuronal activity in real time through “measuring the electrical activity of neuronal cell ensembles on a submillisecond time scale” (Michel, Murray, Lantz, Gonzalez, Spinelli and Grave De Peralta, 2004). Therefore, EEG has a much higher temporal resolution than fMRI. Another limitation of fMRI is that, because the BOLD signal relies on a relatively slow vascular response, both inhibitory and excitatory inputs from other neurons are additive. and consequently the BOLD signal within the neuro will appear to be zero, since the two inputs would cancel each other out (Voos& Pelphrey, 2013, p.3). Although EEG does not present such a problem, unfortunately EEG faces the problem of measuring signals on the surface of the scalp do not directly indicate the location of active neurons in the brain, due to the ambiguity of the underlying electromagnetic inverse static problem (Helmholtz, 1853; Michel, Murray, Lantz, Gonzalez, Spinelli and Grave De Peralta, 2004). “Many different source configurations can generate the same distribution of potentials and magnetic fields on the scalp.” (Michel, Murray, Lantz, Gonzalez, Spinelli, & Grave De Peralta, 2004) Therefore, the maximum activity on some electrodes certainly does not mean that the generators were located in the area beneath them (Michel, Murray, Lantz, Gonzalez, Spinelli, & Grave De Peralta, 2004). Spatial resolution, which is the ability to distinguish differences between nearby spatial locations, determines how clear boundaries between functional areas can be identified.2004.06.001