Microsoft Word Kurzweil, Ray The Singularity Is Near doc

New Tools for Scanning the Brain.
Now imagine, in our computer example above, that we are able to actually place 
precise sensors at specific points in the circuitry and that these sensors are capable of tracking specific signals at very 
high speeds. We would now have the tools needed to follow the actual information being transformed in real time, and 
we would be able to create a detailed description of how the circuits actually work. This is, in fact, exactly how 
electrical engineers go about understanding and debugging circuits such as computer boards (to reverse engineer a 
competitor's product, for example), using logic analyzers that visualize computer signals. 
Neuroscience has not yet had access to sensor technology that would achieve this type of analysis, but that 
situation is about to change. Our tools for peering into our brains are improving at an exponential pace. The resolution 
of noninvasive brain-scanning devices is doubling about every twelve months (per unit volume).
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We see comparable improvements in the speed of brain scanning image reconstruction: 

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The most commonly used brain-scanning tool is fMRI, which provides relatively high spatial resolution of one to three 
millimeters (not high enough to image individual neurons) but low temporal (time) resolution of a few seconds. Recent 
generations of fMRI technology provide time resolution of about one second, or a tenth of a second for a thin brain 
slice. 
Another commonly used technique is MEG, which measures weak magnetic fields outside the skull, produced 
principally by the pyramidal neurons of the cortex. MEG is capable of rapid (one millisecond) temporal resolution but 
only very crude spatial resolution, about one centimeter. 
Fritz Sommer, a principal investigator at Redwood Neuroscience Institute, is developing methods of combining 
fMRI and MEG to improve the spatiotemporal precision of the measurements. Other recent advances have 
demonstrated fMRI techniques capable of mapping regions called columnar and laminar structures, which are only a 
fraction of a millimeter wide, and of detecting tasks that take place in tens of milliseconds.
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fMRI and a related scanning technique using positrons called positron-emission tomography (PET) both gauge 
neuronal activity through indirect means. PET measures regional cerebral blood flow (rCBF), while tMRI measures 
blood-oxygen levels.
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Although the relationship of these blood-flow amounts to neural activity is the subject of some 
controversy, the consensus is that they reflect local synaptic activity, not the spiking of neurons. The relationship of 
neural activity to blood flow was first articulated in the late nineteenth century.
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A limitation of tMRI, however, is 
that the relationship of blood flow to synaptic activity is not direct: a variety of metabolic mechanisms affect the 
relationship between the two phenomena. 

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However, both PET and tMRI are believed to be most reliable for measuring relative changes in brain state. The 
primary method they use is the "subtraction paradigm," which can show regions that are most active during particular 
tasks.
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This procedure involves subtracting data produced by a scan when the subject is not performing an activity 
from data produced while the subject is performing a specified mental activity. The difference represents the change in 
brain state. 
An invasive technique that provides high spatial and temporal resolution is "optical imaging," which involves 
removing part of the skull, staining the living brain tissue with a dye that fluoresces upon neural activity, and then 
imaging the emitted light with a digital camera. Since optical imaging requires surgery, it has been used mainly in 
animal, particularly mouse, experiments. 
Another approach to identifying brain functionality in different regions is transcranial magnetic stimulation 
(TMS), which involves applying a strong-pulsed magnetic field from outside the skull, using a magnetic coil precisely 
positioned over the head. By either stimulating or inducing a "virtual lesion" of (by temporarily disabling) small 
regions of the brain, skills can be diminished or enhanced.
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TMS can also be used to study the relationship of different 
areas of the brain on specific tasks and can even induce sensations of mystical experiences.
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Brain scientist Allan 
Snyder has reported that about 40 percent of his test subjects hooked up to TMS display significant new skills, many 
of which are remarkable, such as drawing abilities.
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If we have the option of destroying the brain that we are scanning, dramatically higher spatial resolution becomes 
possible. Scanning a frozen brain is feasible today, though not yet at sufficient speed or bandwidth to fully map all 
interconnections. But again, in accordance with the law of accelerating returns, this potential is growing exponentially, 
as are all other facets of brain scanning. 
Carnegie Mellon University's Andreas Nowatzyk is scanning the nervous system of the brain and body of a mouse 
with a resolution of less than two hundred nanometers, which is approaching the resolution needed for full reverse 
engineering. Another destructive scanner called the "Brain Tissue Scanner" developed at the Brain Networks 
Laboratory at Texas A&M University is able to scan an entire mouse brain at a resolution of 250 nanometers in one 
month, using slices.
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