Introduction

It has long been known that there is some degree of localization of function in the human brain, as indicated by the effects of traumatic head injury. Work in the middle of the 20th century, notably the direct cortical stimulation of patients during neuro-surgery, suggested that the degree and specificity of such localization of function was far greater than had earlier been imagined. One problem with the data based on lesions and direct stimulation was that the work depended on the study of what were, by definition, damaged brains. During the second half of the 20th century, a collection of relatively noninva-sive tools for assessing and localizing human brain function in healthy volunteers led to an explosion of research in what is often termed "brain mapping.'' The tool that has been developing the most rapidly, and the tool that currently supplies the best volumetric (three-dimensional) picture of activity in the human brain, is fMRI.

Functional MRI uses the physical phenomenon of nuclear magnetic resonance (NMR) and the associated technology of MRI to detect spatially localized changes in hemodynamics that have been triggered by local neural activity. It has been known for more than 100 years that neural activity causes changes in blood flow and blood oxygenation in the brain, and that these changes are local to the area of neural activation. Techniques using radioactive tracers were developed in the mid-20th century to detect metabolic activity correlated with neural activation and to detect blood volume changes correlated with neural activation. In the early 1990s the technique of MRI was successfully adapted to measuring some of these effects noninvasively in humans. The development of fMRI led to a dramatic increase in neuroscience research in human functional brain mapping across the spectrum of psychological functions—from sensation, perception, and attention to cognition, language, and emo-tion—in both normal and patient populations.

Functional MRI makes the future of functional brain imaging particularly exciting for at least three reasons. First, fMRI does not involve ionizing radiation, and therefore it can be used repeatedly on a single subject and even on child volunteers. This permits longitudinal studies and it permits improvement in signal-to-noise ratios if the task being used elicits the same general response when repeated multiple times. Second, technical improvements in fMRI (due to more powerful magnets, more sophisticated imaging hardware, and the development of new methods of experimental design and data analysis) promise to yield improvements in spatial and temporal resolution for the technique. Third, there is a growing effort to integrate the findings based on fMRI with those from other techniques for assessing human brain function, such as electroencephalography (EEG) and magne-toencephalography (MEG), which inherently have much greater temporal resolution. It is likely that major advances in functional brain imaging will be made in the near future, but the associated technologies are complicated. In particular, to understand the technique of fMRI, one must consider a collection of interrelated issues, from physics and physiology to the practicalities of experimental design, data analysis, safety, and costs.

Understanding And Treating Autism

Understanding And Treating Autism

Whenever a doctor informs the parents that their child is suffering with Autism, the first & foremost question that is thrown over him is - How did it happen? How did my child get this disease? Well, there is no definite answer to what are the exact causes of Autism.

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