Compare And Contrast Fmri And Electroencephaloggraphy

Compare and contrast the neuroimaging techniques of ERP and fMRI in terms of their relative advantages and disadvantages. Then, choosing just one technique, discuss how this has been used to address one aspect of cognitive psychology that interests you.
Functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) are two techniques commonly used to noninvasively examine functions within the human brain. When independent of one another these methods fail to provide sufficient information to understand the spatio-temporal aspects of information processing in the human brain. Electroencephalography (EEG) refers to the measurement of electrical activity within the brain, specific neural responses can be calculated by the changes
in electrical activity after the presentation of a stimulus. These changes are relative to a particular event and for that reason are termed event-related potentials (ERPs) (Ganis & Kosslyn 2002). Functional Magnetic Resonance Imaging (fMRI), on the contrary, measures the hemodynamic response relating to the increase in blood oxyhaemoglobin to certain areas of the brain with increased neural activity. fMRI uses blood oxygenation level dependent (BOLD) imaging which relies on the magnetisation difference between oxy- and deoxyhaemoglobin to create the fMRI signal (Arthurs & Boniface 2002). The main advantages and disadvantages of fMRI and event-related potentials are largely complementary of each other. Event-related potentials (ERPs) are recorded from the scalp and therefore provide direct, high temporal resolution signatures of neural activity but offer poor spatial resolution. Conversely, fMRI yield high spatial resolution measures owing to blood flow coupled with the neuronal activity however, have poor temporal resolution (Mangun, Buonocore, Girelli, & Jha 1998). The corresponding strengths and weaknesses of these two neuroimaging techniques, potentially, if utilised together, may develop understandings into the neural basis of behaviour beyond what is possible when using a solitary method (Huster, Debener, Eichele, & Herrmann 2012). The aim of this essay is to examine the complementary features of the two techniques and later discuss how ERPs have been used to address the shifting of our attention and more specifically facial attention.
The main advantage of ERP is that it is able to define the time course of neural information processing with high temporal resolution (Ganis & Kosslyn 2002). The ERP technique allows events of short duration to be reliably recorded as the temporal resolution is around 1msec compared with the poor temporal resolution of the hemodynamic fMRI technique (Menon & Crottaz‐Herbette 2005). fMRI can only measure activity in terms of seconds owing to the slow speed of the BOLD response named the ‘hemodynamic lag’ (Menon & Crottaz‐Herbette 2005); the BOLD response peak may be as long as five seconds after neural firing in that area (Swick, Kutas & Neville 1994). The temporal resolution is supressed in fMRI due to an unclear intrinsic hemodynamic response and a fixed signal-to-noise ratio (Kim, Richter, & Uǧurbil 1997). fMRI merges brain activation information during mental events (Ned Sahin 2015). Conversely, the excellent temporal resolution in ERP allows investigation into underlying cognitive functions including sensory processing and higher level conscious processing. Due to this ERPs have been widely used to examine cognitive dysfunctions. ERP is also often used when studying infants as it is not as sensitive to motion as fMRI. Movement causes distortions and inaccuracies in fMRI which does not occur in ERP (Ganis & Kosslyn 2002).
Another significant advantage of the ERP method is that it is a direct measure of neural activity unlike FMRI that only measures the secondary physiological correlates of neural activity.
fMRI, therefore, is not strictly a quantitative measure of mental activity however, it is more objective than using typical qualitative measures. The BOLD signal associated with fMRI can only measure brain activity indirectly. ERP, on the other hand, provides a direct measure between stimulus and response which is recorded by the electrodes at the scalp (Liotti, Woldorff, Perez, & Mayberg 2000). The BOLD signal in fMRI is at risk of being influenced a number of factors that may cause non-neural changes in the body such as- drugs, age, attention and brain pathology. It is therefore difficult to interpret positive and negative BOLD responses owing to the fact that fMRI is only an indirect measure of neural activity (Morita, Fukuda, Kikuchi, Ikeda, Yumoto, & Sato,
2010).
Functional magnetic resonance imaging (fMRI) is the most predominant method for investigating the brain’s functions. fMRI is supremely advantageous over EMP as it is able to visualize the whole brain and produce compelling images of brain activation (Ned Sahin 2015). fMRI has high spatial resolution which can accurately show detailed images and areas of brain activation within 1mm compared to ERPs poor spatial resolution. EMPs poor magnitude of spatial resolution is often referred to as its ‘inverse problem’ due to the curvature of the cortex (Ganis & Kosslyn 2002). fMRI’s good spatial resolution allows researchers to identify exactly where neural activity is occurring in the brain (Menon & Crottaz‐Herbette 2005). fMRI can also record signals from brain regions unlike in event-related potentials where EEGs are inclined towards the cortical surface (Chen & Li 2012). fMRI is the most commonly used method of neuroimaging as it is widely available and relatively inexpensive compared to PET scans however not as inexpensive as ERPs.
Additionally, a substantial advantage of fMRI’s, compared to EEG recordings, is that fMRI signals are not directly dependent on the laminar or radial neuronal organization unlike ERPs. In ERPs, the simultaneous active neurons need to have a similar orientation for potentials to summate (Woodman 2010). Brain structures that have a laminar orientation, such as the neocortex, contribute significantly more to the EEG recordings than those that have a radial organization such as the thalamus and the basal ganglia. fMRI techniques, by contrast, have considerably more to do with the structure of the underlying vascular bed and are therefore less dependent and less influenced by the orientation of the brain structures (Menon & Crottaz‐Herbette 2005).
Recordings of event-related potentials (ERPs) have demonstrated to be essential measures for developing our knowledge regarding the mechanisms of attention (Luck, Woodman & Vogel 2000). The primary functions of ERP, including its unparalleled ability to measure directly neural activity and its high temporal resolution, make it particularly valuable for testing many aspects of attention including the shifting of attention between tasks and facial recognition (Woodman 2010). ERPs can track brain activity down to 1msec which is incredibly important when studying the voltage fluctuations in response to stimuli, notably facial stimuli. ERPs have been useful for signifying how quickly an individual’s attention can shift from one location or object to another and how swift individuals are at responding to human faces compared to other non-facial stimuli.
Woodman and Luck (2003) support the conception that ERPs are exceptionally beneficial when measuring the speed of switching attention. Woodman and Luck (2003) measured the time individuals took to switch their visual attention between different objects during a difficult visual search task. To investigate how attention switches and changes direction in a short period of time Woodman and Luck (2003) meticulously studied the N2pc ERP component typically observed 200-300ms after the presentation of stimuli. The N2pc ERP component is particularly eminent in attentional research as ERP voltage fluctuations signify a more significant negative response over areas of the visual cortex in the hemisphere contralateral to the situation of attended stimuli within the visual search display (Woodman & Luck 2003). Therefore the N2pc ERP component is proposed to move from the left visual field to the right visual field as an individual shifts their attention from right to left in response to the visual search array. ERPs are able to accordingly measure this shift of attention in terms of milliseconds.
Woodman and Luck (2003) provided supporting evidence for the contralateral notion as they found that as attention shifted between right and left hemifields the N2pc component shifted between left and right hemispheres. Results also indicated that as individuals searched for relevant objects within the visual display their attention corresponded with the significant negative response (N2pc). The ERP recordings found negative responses at approximate 100msec intervals suggesting that attention can shift serially approximately every 100msec in response to object movement or change. A significant advantage of this study compared to behavioral studies of visual search is that the ERP waveform has the ability to provide a constant measure of the distribution of attention. The N2pc component provides a continuous measure of the organization of attention, in response to varied stimuli, virtue of its lateralized distribution (Woodman & Luck 2003). One limitation is that ERPs cannot indicate exactly which parts of the brain are active during the switch of attention to different objects in the visual display (Ganis & Kosslyn 2002). Another limitation of this research is that the ERPs were not recorded in between trials. In 50% of trials participants were asked to search for one particular stimulus and in the other 50% of trials asked to respond to another. The ERPs were not recorded while participant’s requirements were set and therefore the critical brain potentials relating to the shifting of stimulus response mapping in working memory still needs to be evaluated (Barceló, Periáñez, & Knight 2003). A vast amount of attentional research has been conducted into the reasons why human faces capture our attention so rapidly. Recognising faces is a fundamental aspect of social communication and fMRI has identified increased activity of certain regions of the ventral occipital-temporal pathway, such as a lateral part of the fusiform gyrus when responding to faces. However, fMRI cannot give rise to information regarding the timing of facial processing stages like ERP can. ERPs have been used to assess how children, as young as four, can respond to facial stimuli much faster than normal stimuli (Itier & Taylor 2004). ERP research has proposed that the brain may produce a particular reaction to faces that is absent or certainly significantly reduced for alternate visual stimuli (Schweinberger, Pickering, Jentzsch, Burton, & Kaufmann 2002). Attention has been extensively studied, using ERPs, subsequently resulting in the face-specific N170 component which has been pedantically investigated. Human faces consistently elicit a larger negative-going ERP component at occipital-temporal electrodes than other stimuli (Eimer 2011). The N2pc component demonstrates in research concerning facial recognition how individuals can respond rapidly to faces in visual search tasks even if they are classified as irrelevant stimuli (Eimer & Kiss 2007).
Itier and Taylor (2004) found support for N170 and the concept that faces can be recognised much quicker than any other stimuli.
Itier and Taylor (2004) conducted a study involving 450 gray-scale pictures including upright and inverted faces. ERP recordings showed that attention to a facial stimulus was about 25 msec faster than attention to a non-face object. Participants were able to recognise faces faster than other images irrespective of their relevance and orientation in the visual display. These results may provide evidence for specific face perception and recognition abilities in the temporal domain (Itier & Taylor 2004). Results were very similar with those presented in Caldera, Thut, Servoir, Michel, Bovit and Renault (2003) race facial study. Caldera et al 2003 indicated that human’s process faces quicker than objects even if they are not of the same race. ERP results suggested that humans are slightly slower to recognize and respond to a face if it is not the same race but are still significantly faster at acknowledging them than an alternative stimulus. The N2pc component placed further emphasis on the significance of faces compared to other stimuli. Eimer and Kiss (2007) demonstrated how, even when faces were named ‘irrelevant stimuli’, individuals still produced a significant negative response (N2pc). ERP recordings indicated how individuals shifted their attention from relevant stimuli to fearful faces in the visual display. This supports the notion that our
attention is able to shift quickly and attend to human faces more than it is to typical stimuli. This strongly suggests that ERPs provide valuable support that superior facial attention may hold a unique position in human visual perceptual skills owing to its importance for social communication (Caldara et al 2003).