Academic journal article Ethics & Medicine

Can Grey Voxels Resolve Neuroethical Dilemmas?

Academic journal article Ethics & Medicine

Can Grey Voxels Resolve Neuroethical Dilemmas?

Article excerpt


Advances in noninvasive medical imaging have opened new windows into the living brain.Like observatories pointed inward, modern brain scanners routinely capture breathtaking images of the gyral swirls and neuronal clusters that underlie human cerebral nature. These brain portraits are composed of three-dimensional voxels, or volume picture elements, digitally displayed in shades of grey.

Knowledge in neuroscience can be measured in degrees of resolution. Greater neuroimaging resolving power means more finely detailed representations of the human brain. As the brain is the physical correlate of the mind, its grey matter and intricate interconnections are subject to scientific investigation. Neuroimaging methods increasingly are able to map out, voxel by voxel, the neurobiological pathways underlying all aspects of thought and behavior, including those involved in moral judgment and ethical reasoning.1-3

Whether clarity in neuroimaging might help to resolve, not only clinical questions, but also ethical grey matters, is a prime question for neuroethics. The repertoire of voxels has so multiplied that it is now possible to speculate whether, from a science of the brain, one can derive a coherent and valid system of ethics. Psychologist Michael Gazzaniga has proposed that, "there could be a universal set of biological responses to moral dilemmas, a sort of ethics, built into our brains."4 Images have always profoundly influenced cultural perceptions of human nature. To the extent that neuroimaging informs a brain-based model of ethics, its fundamental unit of significance is the voxel.

To begin to explore the implications of a voxel-based paradigm for ethical theory, it is helpful to examine, not just the quality of images, but also the methods and presuppositions of neuroimaging. Implicit in every voxelous reconstruction of the brain is the idea that the brain is virtually, if not essentially, reducible to matter. Reductionism can clarify, but it can also mislead. Vibrant voxels may elucidate pertinent facts. Exclusive attention to them may overlook important truths.

Neuroimaging is a product of the last hundred or so years, with the greatest progress having occurred in the last three decades. Following Röntgen's invention of the x-ray machine in 1895, for much of the 20th century, visualization of the diseased brain was possible only through pneumoencephalography, a painful procedure in which air was injected into the spine and allowed to rise to outline the contours of the brain as seen on a skull x-ray. The first computed tomography (CT) scan in clinical use at Mayo Clinic in 1973 supplanted pneumoencephalography with a hundred-fold increase in the resolution of brain imaging. Presenting anatomic images slice by slice, its spatial resolution was coarse by today's standards with a field of view of 13 mm per voxel. By contrast, current CT technology achieves sharp spatial resolution with typical fields of view of 0.7 mm, and emerging methods of multidetector row high resolution CT achieve 0.4 mm per voxel. CT angiography now achieves resolution of the major intracranial blood vessels about as clearly as early CT resolved such larger structures as the brain's lobes and ventricles.

Whereas CT utilizes ionizing radiation to measure tissue density, magnetic resonance imaging (MRI) utilizes radiofrequency pulses to define soft tissue molecular composition at resolutions of 1-3 mm per voxel. More powerful 8 Tesla research magnets can achieve high resolution images with voxels corresponding to just 0.2 mm. This level of imaging detail compares to the 0.01-0.05 mm size of most neurons.

Ever sharper shades of spatial resolution seem at first to suggest that, if only the brain were to be imaged in sufficient detail, then all the brain is and does might be explained. The structure of matter, however, is not all there is. Exact knowledge of the brain's shape, its configuration, its density and spatial orientation, even the atoms that make up its grey matter, while necessary for accurate neuroscience, yet are insufficient. …

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