Introduction- Neuroimaging refers to various techniques that involve brain-scanning and assist in observing the different levels of activity in the brain of a participant while they are performing some psychological tasks. These techniques are used to directly or indirectly create an image of the structure, function and pharmacology of the nervous system (de Notaris et al., 2013). Various attempts had been taken towards the end of nineteenth century, to discover the different mental processes that drive all human functions and behavior. It was a common assumption that mental processing in the brain is unconsciously produced. Reaction time and response accuracies were used to study this field. The neural basis of cognition was studied among patients who suffered from brain damage in the 1970s and the assumption was made that brains are composed of modules that are arranged in a structural and functional pattern. The history of neuroimaging began with the use of pneumoencephalography in the 1990s (Webb, 2013).
This altered the relative density of the brain and a better x-ray image was obtained. Position Emission Tomography (PET), Computed tomography (CT) and functional Magnetic Resonance Imaging (fMRI) scans are the most commonly used neuroimaging techniques used to study neural cognition. This essay will illustrate the advantages and disadvantages of neuroimaging techniques and whether it can be considered as the best method to detect mental processes.
Advantages of neuroimaging techniques- Functional techniques are considered as the mainstay in studying cognitive neuroscience owing to their ability to help us in determining the association of neural activity in the brain with the ability to perform complex cognitive tasks. It also determines the neural activity during illness (Wintermark et al., 2015). This approach works by identifying and isolating the different brain structures that are involved in complex cognitive processes. These techniques produce images of the brain, without the requirement of any skin incision, surgery, or direct contact with the internal organs of the body. The major advantage of these techniques lies in the fact that they are noninvasive procedures that result in visualization of the entire structure and functionality of human brain.
The neuroimaging techniques help in comparing the activation levels among different subjects and further assists in discovering the association between performance levels among the subjects and their level of activation (Boly et al., 2016). In addition, the technique can also be utilized to compare between various trials that further helps in associating the activated regions of the brain with presence of errors in the trial. Generally, two types of imaging agents are used for these studies.
- Passive agents, which modulate an external signals. Higher doses of passive contrast agents are used to delineate endogenous contrasts.
- Probes such as, bioluminescent dyes and radiotracers that produce autonomous signals. Some fluorescent probes and MRI contrast agents lead to transformation of an external signal (Simó et al., 2013).
Furthermore, the techniques help to demonstrate that human beings not suffering from any neurological damage or lesions are able to recruit specific regions of the brain to carry out cognitive processes.
Advantages of neuroimaging in neuropsychological studies- Neuropsychological studies focus on the structure and function of the brain and relate them to human behavior and psychological processes. However, they do not concentrate on the cognitive processes of the brain. Neuroimaging studies overcome this drawback and help to gain a better understanding of cognition (Beauregard, 2014). They help in drawing inferences regarding engagement of particular cognitive processes from activated brain regions. Lesions in the brain that result in long term memory deficits make it difficult to figure out associations between memory encoding and retrieval. However, neuroimaging studies provide images that help in recognition of brain regions that are associated with storage, encoding and retrieval of long term memory (Zatorre, Fields & Johansen-Berg, 2012).
The lesion methods fail to distinguish between the functions of undamaged regions and damaged focal regions of the brain. This makes it difficult to interpret the overlay of plots. Moreover, intact regions of the brain can get incapacitated after suffering damage (Fox et al., 2016). Thus, it can be stated that despite the complexities of the brain structures and its functioning, the advances in neuroimaging studies are efficient in providing relevant scientific insights about the brain (Guillory & Bujarski, 2014).
Advantages of neuroimaging compared to behavioural methods- There are specific advantages of PET and fMRI in comparison to behavioural methods. Behavioural methods fail to measure all the cognitive processes of the brain such as, reaction time. Further, they are unable to measure accuracy of the studies. On the other hand, neuroimaging techniques enable in studying the subtle cognitive processes such as memory formation and language comprehension (Bernardy et al., 2012). Thereby, they help in mapping brain activities and provide detailed information about the temporal features of all relevant neural processes.
According to Henson (2005) haemodynamic techniques are used to measure variations in the metabolic demands owing to differences that arise in the neuronal mean activity. This leads to changes in local blood supply. The Blood Oxygenation Level Dependent (BOLD) signal, measured by fRMI and the PET signal interpret the complex interaction of oxygenation levels, blood flow and its volume. They help in reflecting several seconds of neural activity integration.
Furthermore, clues are obtained regarding the sensory integration mechanism while determining the circumstances that result in production of activity in visual cortex under the influence of a tactile stimulus, while performing neuroimaging. However, behavioural studies fail to provide such data (Beer & Williams, 2015). Furthermore, contact with other information sources such as, such as, anatomical data that depicts connection between different brain regions and single-cell recording data can be obtained from imaging studies. This assists establishment of cognitive theories (Henson, 2005).
Evidence from neuroimaging studies also suggest that visual stimuli repetition results in haemodynamic response reduction in the extrastriate occipitotemporal cortex (Kahl, Winter & Schweiger, 2012). This reduction is able to survive various intervening stimuli and becomes equal to amount of perceptual priming.
The concept of function-to-structure mapping indicates several situations where functional imaging becomes pertinent in identifying the engagement of different brain locations and the underlying psychological process. It helps in forming a bridge between psychological theories and neuroimaging data. The function-to-structure deduction depicts implications of brain activity in different experimental conditions that have qualitative dissimilarities between them (Tamangani, 2016). Thus, the null hypothesis gets rejected and no difference exists between them. PET traces have proved effective in discovering several drug targets for Alzheimer’s disease by binding the plaque forming beta-amyloid and tau proteins (Zhang et al., 2012). O-H2O is used as a gold standard in order to study the pathological changes of the brain. Advantages of MRI lie in the fact that it detects an endogenous contrast agent with high sensitivity.
There were several criticisms that compared neuroimaging to phrenology. However, there are significant difference between them with respect to the structures that are investigated, the functions being analysed and the fact that functional neuroimaging studies are interventional. The factors can be manipulated and the system being investigated can be perturbed to observe changes in brain activity. Other criticisms were associated with the correlational nature of the data, the independence of algorithms and the fact that functional neuroimaging does not provide direct information on how a task is performed (Henson, 2005).
According to the theory proposed by Kosslyn, the information that is stored in associative memory is not only utilized to guide the mechanisms that control attention shift but also to prime the representations of the encoding system. It was proposed that cooperative computation is formed by efferent connections (Kosslyn, 1999). He proposed that two minimally tasks are compared using neuroimaging experiments. Varying a single aspect of a task each time produces better results. In addition, it identified areas of the brain that performs visual information processing and also stated that the putative functions of each area need not be studied separately. However, a study featuring the entire system can be designed that focuses on a plethora of tasks.
The second question addressed was related to the areas that implement simple system, and found that comparison between additional activation of brain areas when subordinate terms and entry-level terms were evaluated using PET, helped in identifying the areas related to associative memory. It suggested that activation of an area was not adequate to infer its contribution to a certain performance. It also helped in establishing that neuroimaging can help in revealing distinctions (Kosslyn, 1999). It was further suggested that disrupting a particular area can help in discovering whether the process implemented plays a functional role on conferring ability (Karatas & Toy, 2014). In addition, it stated that neuroimaging acts a valuable tool in providing information on the mechanism that underlies the working of various structures and processes.
Disadvantages of neuroimaging techniques- It helps in providing only correlation between the cognitive process and specific brain locations. PET and fMRI fail to provide information on the function of brain regions and their association between the cognitive processes. The activation of a particular task in the left hemisphere can appear completely bilateral owing to the presence of homotopic neural connections between the two hemispheres. Neuroimaging techniques can therefore make the roles of the left hemisphere appear as that of both the hemispheres. Neuroimaging studies make it difficult to discover the regions that do not undergo any change and are constantly functioning (Nam, Barrack & Potter, 2014).
The imaging studies fail to depict any changes in blood flow. This results in images that show no involvement of the concerned area in the cognitive process and thereby gives misleading results.
PET scans are widely used to generate images that demonstrate structural abnormalities, neuronal functionalities and biochemical changes in the brain. However, a major setback to PET is that they afford relatively poor spatial resolution. The 2D or 3D images formed are often not clear and have poor resolution (Moriarty, Langleben & Provenzale, 2013). This makes it difficult to visualize the regions of the brain and produces incorrect results. Therefore, PET is often used in combination with fMRI. In addition, the radiations can result in several health risks even on application in small doses.
Furthermore, the use of MRI and fMRI imaging techniques is imperative to neurobiology research and in complex medical cases. The fact that they do not rely on the use of ionizing harmful radiations makes them superior. However, they do have some disadvantages as well. The major risk associated with MRI the presence of metal equipments such as any implants or pacemaker in the person bring subjected to the procedure (Rana, Masroor & Khan, 2013). The metal bodies often create safety hazards. Moreover, these techniques can result in bouts of claustrophobia among certain individuals. This may occur due to the fact that extremely tight spaces are used to conduct the scans. Individuals, exposed to these techniques for a prolonged time period may also suffer from hearing impairments due to the loud noise generated from the instruments. Page (2006) further argues on the fats proposed by Henson, which claim that unwarranted inference of two functions can be avoided by making a specific detail for the neural mechanisms that are being precisely considered. However, these theories are remotely practicable for most real time cognitive processes. The arguments also suggest that the trend of cognitive neuroimaging would create less negative effects if the imaging methods become cheap and user friendly. He also suggested that functional neuroimaging studies absorb relatively large proportion of funding.
In addition, Page argued that cognitive psychology should get a better supply of mindscanners in order to be a successful scientific field. He suggested that mind scanners are able to identify the areas that present significant theoretical disputes and should be capable to design, run and analyze the experimental tests. Therefore, he suggested that functional neuroimaging plays a significant role in cognitive theory development when accompanied with a secure supply of mindscanners.
He further argued that media outlets publish articles with pictures that suggest that scientists have discovered a part of the brain that activates in people performing a certain task. Page stated that if the general public is given the idea that production of such pictures represents the work done by cognitive psychologists, then it would suggest that psychologists who do not publish such pictures fail to perform their job and would increase the risk of tyranny of graphics (Page, 2006).
Furthermore, no good evidences can be obtained that suggest that similar function can be performed in two different regions. Therefore, there are some doubts related to the contribution of functional neuroimaging techniques in understanding cognitive process (Page, 2006). In addition, it can be stated that over relying on neuroimaging techniques, increase provisions for recognition of cognitive psychology as a branch of medical science (Mather, Cacioppo & Kanwisher, 2013). This can lead to long term problems where an increase in funding for neuroimaging to study cognitive approaches might give rise to questions on their immediate benefits on human health.
Conclusion- To summarise, neuroimaging generally follows a follows a neurological examination where the physician wants further investigation of the underlying cause that might have resulted in the neurological disorder. The imaging can be either structural or functional imaging. While the former deals with providing an image that depict a detailed structure of the nervous system and helps in diagnosing injuries and intracranial diseases, the latter diagnoses lesions in the brain and is often used for research on cognitive psychology. The imaging techniques are also utilized to build brain-computer interfaces.
Therefore, these techniques work best in understanding the integration between different areas of the brain during the operation of various mental processes. To conclude, neuroimaging mapping provides evidence for the high degree of specialization among the different brain regions that provides a deeper understanding of cognitive psychology. However there are major disadvantages as well. Thus, it cannot be stated whether neuroimaging is superior to other conventional methods to study neural cognition.
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