Summary
Thereafter, the record can be compared with the electrical activity of another record comprised of composite recordings of many 'normal' brains.8 These signals can, as in the case of positron emission tomography (PET), single-photon emission computed tomography (SPECT), and structural and functional MRI, be fed into a computer that stores the data and uses the information to form or reconstruct an image of the brain.9 In order to enhance visual impact, the image produced is generally color-coded along a spectrum from blue and green to red and yellow to reflect the varying degrees of activity in specific regions of the brain.10 Functional brain imaging may have an important role in our understanding of the relationship of brain processes to behavior.11 It offers the possibility to couple an image with neurocognitive and emotional functioning.12 As we will see, some of these functioning imaging modalities, particularly PET and fMRI, go further to integrate brain function with features of molecular and neural circuitry information.13 Basic functional imaging can be achieved through a variety of methods, from PET and SPECT to quantitative EEG, MEG, and fMRI, each of which measures a different physical property of the brain. To date, however, among these different imaging technologies, PET and fMRI have been the most technologically advanced, and have had the broadest application in the courtroom.14 In the case of PET, the most frequently studied biological process has been energy metabolism.15 This is primarily because energy metabolism is closely linked to brain function, although in a very complex way.16 Energy metabolism and, therefore, brain function, is revealed through the study of three components of energy, which are normally physiologically coupled. 17 These components are glucose metabolism, oxygen metabolism, and cerebral blood flow.18 Glucose metabolism is studied through the use of an analogue of glucose (i.e. deoxyglucose) labeled with a radiotracer such as Flourine-18 or Carbon-11.19 Oxygen metabolism is investigated with the use of Oxygen-15, and cerebral blood flow with Oxygen-15 labeled water.20 Because it is a tracer method, PET has the distinct advantage of being thus far the best modality for the detection of a wide variety of biochemical processes.21 In fact, its only limitation is chemical ingenuity and its inherent high sensitivity.22 Furthermore, one of its advantages is that PET has a high degree of quantification accuracy regarding changes pre- and post- intervention in brain regions with altered brain perfusion or metabolism.23 Unfortunately, interpretable PET data are almost never available for any individual prior to the incident, behavior or brain insult that led to the legal proceeding.24 Nevertheless, in current standardized settings, which are rigorously defined, PET data are very reproducible.25 MRI, on the other hand, relies upon a particular physical property of the hydrogen atom-the inherent spin of its atomic nucleus-that enables all of the hydrogen nuclei in water to be oriented similarly in the presence of a very strong homogeneous magnetic field.
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Extract
The Brain and Behavior: Limitations in the Legal Use of Functional Magnetic Resonance Imaging
I. INTRODUCTION
Brain imaging is one of the most remarkable technological advances towards understanding the relationship of behavior to brain anatomy and physiology. Brain images provide insight to understanding behavior. Additionally, the images themselves carry great impact, particularly when used to show differences in either the anatomy or the biological functioning of two different brains. For these reasons, brain images have increasingly been used in both criminal and civil trials.After describing some general features of brain imaging, we will focus on functional magnetic imaging (fMRI), as many believe this technology has the most potential for advancing our understanding of how parts of the brain function, including perhaps linking specific functions with cognition and behavior. Brain imaging as a field is vast and therefore our discussion will be limited. First, we will assess the advantages and limitations of fMRI, including research efforts towards standardizing equipment thereby assuring reliability and reproducibility. second, we will address the extent to which fMRI links brain function to behaviors. We will then discuss the enhancing benefits of combining of fMRI with other imaging technologies, like electroencephalography (EEG)1 and magnetoencephalography (MEG).2 Finally, we will consider the relevance of fMRI for law, especially the potential for assessing personal responsibility and detecting truth and lies during interrogation.II. BASICS OF BRAIN IMAGINGWhether structural or functional, brain imaging can involve a variety of methods. Each method is geared towards detecting and measuring specific signals of some property related to the brain with a detection device that is usually outside of the brain.3 Signals that are detected vary from electrical activity in the brain,4 to magnetic dipoles induced from outside the brain,5 to radioactive events through the injection of radioactive tracers.6 These signals measure different properties of brain tissue and vary widely in parameters, including specificity, sensitivity, temporal and spatial resolution, and in their fidelity towards reflecting the physiological processing being studied.7 In addition, the images created are not immutable. Although some properties of the brain are largely invariant at the functional level, adaptation in the service of homeostasis and as a necessary response to the varying environment will insure that the micro-anatomy must be ever-changing.Regardless of the source, signals result in distinctive patterns that wo...See the full content of this document
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