16. Steve Cullen, In-Stat, September 2008, www.instat.com.
| Year | Mbits | Bits |
|---|---|---|
| 1971 | 921.6 | 9.216E+08 |
| 1972 | 3788.8 | 3.789E+09 |
| 1973 | 8294.4 | 8.294E+09 |
| 1974 | 19865.6 | 1.987E+10 |
| 1975 | 42700.8 | 4.270E+10 |
| 1976 | 130662.4 | 1.307E+11 |
| 1977 | 276070.4 | 2.761E+11 |
| 1978 | 663859.2 | 6.639E+11 |
| 1979 | 1438720.0 | 1.439E+12 |
| 1980 | 3172761.6 | 3.173E+12 |
| 1981 | 4512665.6 | 4.513E+12 |
| 1982 | 11520409.6 | 1.152E+13 |
| 1983 | 29648486.4 | 2.965E+13 |
| 1984 | 68418764.8 | 6.842E+13 |
| 1985 | 87518412.8 | 8.752E+13 |
| 1986 | 192407142.4 | 1.924E+14 |
| 1987 | 255608422.4 | 2.556E+14 |
| 1988 | 429404979.2 | 4.294E+14 |
| 1989 | 631957094.4 | 6.320E+14 |
| 1990 | 950593126.4 | 9.506E+14 |
| 1991 | 1546590618 | 1.547E+15 |
| 1992 | 2845638656 | 2.846E+15 |
| 1993 | 4177959322 | 4.178E+15 |
| 1994 | 7510805709 | 7.511E+15 |
| 1995 | 13010599936 | 1.301E+16 |
| 1996 | 23359078007 | 2.336E+16 |
| 1997 | 45653879161 | 4.565E+16 |
| 1998 | 85176878105 | 8.518E+16 |
| 1999 | 1.47327E+11 | 1.473E+17 |
| 2000 | 2.63636E+11 | 2.636E+17 |
| 2001 | 4.19672E+11 | 4.197E+17 |
| 2002 | 5.90009E+11 | 5.900E+17 |
| 2003 | 8.23015E+11 | 8.230E+17 |
| 2004 | 1.32133E+12 | 1.321E+18 |
| 2005 | 1.9946E+12 | 1.995E+18 |
| 2006 | 2.94507E+12 | 2.945E+18 |
| 2007 | 5.62814E+12 | 5.628E+18 |
17. “Historical Notes about the Cost of Hard Drive Storage Space,” http://www.littletechshoppe.com/ns1625/winchest.xhtml; Byte magazine advertisements, 1977–1998; PC Computing magazine advertisements, 3/1999; Understanding Computers: Memory and Storage (New York: Time Life, 1990); http://www.cedmagic.com/history/ibm-305-ramac.xhtml; John C. McCallum, “Disk Drive Prices (1955–2012),” http://www.jcmit.com/diskprice.htm; IBM, “Frequently Asked Questions,” http://www-03.ibm.com/ibm/history/documents/pdf/faq.pdf; IBM, “IBM 355 Disk Storage Unit,” http://www-03.ibm.com/ibm/history/exhibits/storage/storage_355.xhtml; IBM, “IBM 3380 Direct Access Storage Device,” http://www.03-ibm.com/ibm/history/exhibits/storage/storage_3380.xhtml.
18. “Without Driver or Map, Vans Go from Italy to China,” Sydney Morning Herald, October 29, 2010, http://www.smh.com.au/technology/technology-news/without-driver-or-map-vans-go-from-italy-to-china-20101029-176ja.xhtml.
19. KurzweilAI.net.
20. Adapted with permission from Amiram Grinvald and Rina Hildesheim, “VSDI: A New Era in Functional Imaging of Cortical Dynamics,” Nature Reviews Neuroscience 5 (November 2004): 874–85.
The main tools for imaging the brain are shown in this diagram. Their capabilities are depicted by the shaded rectangles.
Spatial resolution refers to the smallest dimension that can be measured with a technique. Temporal resolution is imaging time or duration. There are tradeoffs with each technique. For example, EEG (electroencephalography), which measures “brain waves” (electrical signals from neurons), can measure very rapid brain waves (occurring in short time intervals), but can only sense signals near the surface of the brain.
In contrast, fMRI (functional magnetic resonance imaging), which uses a special MRI machine to measure blood flow to neurons (indicating neuron activity), can sense a lot deeper in the brain (and spinal cord) and with higher resolution, down to tens of microns (millionths of a meter). However, fMRI operates very slowly compared with EEG.
These are noninvasive techniques (no surgery or drugs are required). MEG (magnetoencephalography) is another noninvasive technique. It detects magnetic fields generated by neurons. MEG and EEG can resolve events with a temporal resolution of down to 1 millisecond, but better than fMRI, which can at best resolve events with a resolution of several hundred milliseconds. MEG also accurately pinpoints sources in primary auditory, somatosensory, and motor areas.
Optical imaging covers almost the entire range of spatial and temporal resolutions, but is invasive. VSDI (voltage-sensitive dyes) is the most sensitive method of measuring brain activity, but is limited to measurements near the surface of the cortex of animals.
The exposed cortex is covered with a transparent sealed chamber; after the cortex is stained with a suitable voltage-sensitive dye, it is illuminated with light and a sequence of images is taken with a high-speed camera. Other optical techniques used in the lab include ion imaging (typically calcium or sodium ions) and fluorescence imaging systems (confocal imaging and multiphoton imaging).