Thursday, April 18, 2019

Functional Magnetic Resonance Imaging Essay Example | Topics and Well Written Essays - 3000 words

Functional Magnetic Resonance Imaging - turn out ExamplefMRI measures maven employment indirectly, namely by measuring change in atomic number 8 content this is called the Blood Oxygenation Level Dependent (BOLD) contrast mechanism.However, fMRI has certain limitations. For instance, the fMRI foretell reflects changes in oxygen content with high but insufficient spatial-time resolution. Hemodynamics in response to neuronal activity is revealed on a spatial-temporal scale far longer than the neuronal activity itself. Here, so-called temporal blurring of the fMRI signal is caused by both inertance and residual effects. In spite of much(prenominal) obstacles, changes in neural activity associated with various(prenominal) trials or components of a trial in a line of work can be observed. Moreover, it is possible to enchant brain activity associated with a single momentary cognitive act of mentally rotating a stimulus, without sanctuary to averaging over events (Buckner & Logan 2001, p. 31). Special fMRI experimental designs such as event-related fMRI designs are required in these cases.thither are numerous difficulties in separating the processing roles of specific brain areas. Usually such withdrawal is provided either by well matched task comparisons or through convergence crossways multiple studies. However, brain activity changes can be relative changes between pairs of tasks, gradual or even nonlinear changes across a series of tasks, or correlations between different tasks. How can tasks and trials within a task be constructed to separate brain cognitive operations This is a key problem of fMRI experimental design. There are several approaches for its solving. The basic approach is to have subjects engage in a target behavioral task for a period of time and then contrast that task period with periods where subjects perform a reference task. Here, the subject might perform a target task, and the measurement obtained during the performance of that task would be contrasted with a measurement obtained when the subject performed a matched reference task. How to substantiate this approach It is obvious that brain activity will change between the two task states and therefore will correlate selectively with the manipulated task demands. When using fMRI, images are taken of the brain repeatedly and in sequence. Brain areas of activation are place by examining which specific regions change signal intensity as the task state changes from the reference thoughtfulness to the target task. Then, statistical procedures ranging from direct comparisons between task states to more sophisticated estimations of correlations among task states can be employed to identify those regions whose activity change is unlikely to occur by chance. Unfortunately, tasks designed by such approach may cause differences in the processing strategies adopted by subjects during task performance by means of the blocking of trials, which may result in differentia l patterns of neural activity that do non have to do with the item-specific processes elicited by the individual trials. This issue can appear in frail forms in cognitive paradigms where subject strategies may be

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