Other lab techniques include PET (positron emission tomography, a nuclear medicine imaging technique that produces a 3-D image), 2DG (2-deoxyglucose postmortem histology, or tissue analysis), lesions (involves damaging neurons in an animal and observing the effects), patch clamping (to measure ion currents across biological membranes), and electron microscopy (using an electron beam to examine tissues or cells at a very fine scale). These techniques can also be integrated with optical imaging.
21. MRI spatial resolution in microns (μm), 1980–2012:
22. Spatial resolution in nanometers (nm) of destructive imaging techniques, 1983–2011:
23. Spatial resolution in microns (μm) of nondestructive imaging techniques in animals, 1985–2012:
| Year | Finding | |
|---|---|---|
| 2012 | Resolution | 0.07 |
| Citation | Sebastian Berning et al., “Nanoscopy in a Living Mouse Brain,” Science 335, no. 6068 (February 3, 2012): 551. | |
| URL | http://dx.doi.org/10.1126/science.1215369 | |
| Technique | Stimulated emission depletion (STED) fluorescence nanoscopy | |
| Notes | Highest resolution achieved in vivo so far | |
| 2012 | Resolution | 0.25 |
| Citation | Sebastian Berning et al., “Nanoscopy in a Living Mouse Brain,” Science 335, no. 6068 (February 3, 2012): 551. | |
| URL | http://dx.doi.org/10.1126/science.1215369 | |
| Technique | Confocal and multiphoton microscopy | |
| 2004 | Resolution | 50 |
| Citation | Amiram Grinvald and Rina Hildesheim, “VSDI: A New Era in Functional Imaging of Cortical Dynamics,” Nature Reviews Neuroscience 5 (November 2004): 874–85. | |
| URL | http://dx.doi.org/10.1038/nrn1536 | |
| Technique | Imaging based on voltage-sensitive dyes (VSDI) | |
| Notes | “VSDI has provided high-resolution maps, which correspond to cortical columns in which spiking occurs, and offer a spatial resolution better than 50 μm.” | |
| 1996 | Resolution | 50 |
| Citation | Dov Malonek and Amiram Grinvald, “Interactions between Electrical Activity and Cortical Microcirculation Revealed by Imaging Spectroscopy: Implications for Functional Brain Mapping,” Science 272, no. 5261 (April 26, 1996): 551–54. | |
| URL | http://dx.doi.org/10.1126/science.272.5261.551 | |
| Technique | Imaging spectroscopy | |
| Notes | “The study of spatial relationships between individual cortical columns within a given brain area has become feasible with optical imaging based on intrinsic signals, at a spatial resolution of about 50 μm.” | |
| 1995 | Resolution | 50 |
| Citation | D. H. Turnbull et al., “Ultrasound Backscatter Microscope Analysis of Early Mouse Embryonic Brain Development,” Proceedings of the National Academy of Sciences 92, no. 6 (March 14, 1995): 2239–43. | |
| URL | http://www.pnas.org/content/92/6/2239.short | |
| Technique | Ultrasound backscatter microscopy | |
| Notes | “We demonstrate application of a real-time imaging method called ultrasound backscatter microscopy for visualizing mouse early embryonic neural tubes and hearts. This method was used to study live embryos in utero between 9.5 and 11.5 days of embryogenesis, with a spatial resolution close to 50 μm.” | |
| 1985 | Resolution | 500 |
| Citation | H. S. Orbach, L. B. Cohen, and A. Grinvald, “Optical Mapping of Electrical Activity in Rat Somatosensory and Visual Cortex,” Journal of Neuroscience 5, no. 7 (July 1, 1985): 1886–95. | |
| URL | http://www.jneurosci.org/content/5/7/1886.short | |
| Technique | Optical methods |
Chapter 11: Objections
1. Paul G. Allen and Mark Greaves, “Paul Allen: The Singularity Isn’t Near,” Technology Review, October 12, 2011, http://www.technologyreview.com/blog/guest/27206/.
2. ITRS, “International Technology Roadmap for Semiconductors,” http://www.itrs.net/Links/2011ITRS/Home2011.htm.
3. Ray Kurzweil, The Singularity Is Near (New York: Viking, 2005), chapter 2.
4. Endnote 2 in Allen and Greaves, “The Singularity Isn’t Near,” reads as follows: “We are beginning to get within range of the computer power we might need to support this kind of massive brain simulation. Petaflop-class computers (such as IBM’s BlueGene/P that was used in the Watson system) are now available commercially. Exaflop-class computers are currently on the drawing boards. These systems could probably deploy the raw computational capability needed to simulate the firing patterns for all of a brain’s neurons, though currently it happens many times more slowly than would happen in an actual brain.”
5. Kurzweil, The Singularity Is Near, chapter 9, section titled “The Criticism from Software” (pp. 435–42).
6. Ibid., chapter 9.
7. Although it is not possible to precisely determine the information content in the genome, because of the repeated base pairs it is clearly much less than the total uncompressed data. Here are two approaches to estimating the compressed information content of the genome, both of which demonstrate that a range of 30 to 100 million bytes is conservatively high.
1. In terms of the uncompressed data, there are 3 billion DNA rungs in the human genetic code, each coding 2 bits (since there are four possibilities for each DNA base pair). Thus the human genome is about 800 million bytes uncompressed. The noncoding DNA used to be called “junk DNA,” but it is now clear that it plays an important role in gene expression. However, it is very inefficiently coded. For one thing, there are massive redundancies (for example, the sequence called “ALU” is repeated hundreds of thousands of times), which compression algorithms can take advantage of.