Part II: Applications
Motor and Sensory Mapping

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Clinical importance

The use of fMRI in the clinical setting benefits patients insomuch as it allows neurosurgeons to be aware of and to navigate the precise location of patient-specific eloquent cortices and any structural anomalies that may have developed from a tumor.2 This anatomic/functional preview facilitates the creation of more effective patient-specific treatment plans. Before the use of fMRI, the preoperative location of eloquent cortices and their relationship to the lesion was determined based on the

Neuroanatomic Review

A brief review of basic anatomy of the motor and sensory system facilitates the discussion of paradigm selection. The motor and sensory systems both have a topographic organization; in other words, motor and sensory functions are mapped to specific locations on the cortex.1 The foot and leg are represented along the interhemispheric fissure, the hand lateral to that of the foot and leg, and the tongue and face lateral to that of the hand (Fig. 2).

Voluntary movement is performed through a

Cortical plasticity/reorganization

fMRI can provide an insight into cortical plasticity/reorganization, a phenomenon that can add new layers of complexity to the analysis of fMRI data and to the planning and resection of brain lesions. Cortical reorganization is thought to occur when an area of the brain is no longer able to complete its function, which causes another area of the brain to attempt to compensate in an effort to maintain function.11, 31 Cortical reorganization is an area of intense investigation both in the basic

Analysis Overview

fMRI data analysis seeks to determine active areas through identification of voxels in the brain with statistically significant changes in blood oxygenation–level dependent (BOLD) signal from baseline to activation.11 The goal is to pinpoint voxels that show changes in signal related to the paradigm performed (the timing of the ON/OFF periods).11, 12 Surgeons can then consider the locations of such active areas when planning surgery. Signal changes, however, are very small, between 0.5% and

Artifacts and other pitfalls in clinical fMRI

Artifacts from various sources can affect the results of fMRI data. Unwanted movement can produce motion artifacts; such motion can include larger head or body movement or simple periodic fluctuations in heart rate and respiration (pulsatile artifact).12, 31 Often leading to false-negative/false-positive results, head motion can inadvertently move voxels of a high signal intensity to locations of low signal intensity.31 Patient comfort must also be ensured to minimize extra motion and

Current Research for Future Applications

Current research with fMRI is revealing exciting future applications for enhanced use in presurgical planning and areas of treatment/rehabilitation. With increased use and understanding of the technique, fMRI-guided presurgical planning concerning atypical anatomy13 (eg, disruptions caused by tumors and tumor neovasculature) will improve and become more reliable. In patients with gliosis, for example, in whom functional areas surrounding the lesion may be distorted due to mass effect,12

Summary

fMR is important to the understanding of brain function, structure, and mechanism as well as to the localization of critical motor, speech, and cognitive function. It has many advantages when compared with other methods of neuroimaging and functional mapping: it is noninvasive, it does not entail the use of radioactive isotopes, it is easily repeatable, and it has no known risks.2 Its use in presurgical mapping, such as locating motor, sensory, language, and/or memory functional areas in

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