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Science Frontiers ONLINE No. 85: Jan-Feb 1993 |
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Our Chemical Brain
Is our brain merely a network of neurons pulsing with electrical signals -- like the circuits of a computer? Such is the accepted picture of the brain. Unquestionably the brain does rely in part upon the transmission of electrical signals for some of its operations, but it now appears that there is a complementary mode of communication that relies upon chemistry rather than electricity.
While the fastest way to transmit signals in the brain seems to be along the neurons and across their points of contact, the synapses, other signals may travel -- a bit more slowly -- by what is termed "volume transmission." Volume transmission is like broadcasting radio waves in three dimensions, except that in the brain the radio waves are replaced by the diffusion of chemical signals. L.F. Agnati et al explain:
"...our experiments have shown that neurons also release chemical signals into the extracellular space that are not necessarily detected by neighboring cells but by cells far away, in the same way hormones released by a gland into the bloodstream can have effects on cells far away. These processes occur on much longer time scales than does synaptic transmission, and they probably play a distinct role, perhaps regulating the brain's responses to synaptic signals. ....."We might speculate that volume transmission is involved in the neuroendocrine system and the central autonomic system. Changes in the activity of the brain during sleep and wakefulness, relative levels of alertness, mood and sensitivity to pain may be highly dependent on volume transmission. Thus, although information regarding to location of pain is carried by the circuitry of the nervous system, the intensity and duration of the pain may be somewhat modulated by the ambient homoral signals. In this respect, acupuncture may also be a phenomenon that is dependent on volume transmission."
(Agnati, Luigi F., et al; "Volume Transmission in the Brain," American Scientist, 80:362, 1992.)
Questions. (1) Is there a connection between volume transmission and the analog transmission of brain signals hypothesized by R.O. Becker (SF#81)? (2) Can a computer really be programmed to think like a human if it is all wires without something analogous to volume transmission; i.e. is artificial intelligence really possible? (3) How and why did at least two forms of information transmission evolve? (4) Might there still be other modes of information transmission and processing in the brain -- perhaps something associated with genius, psi, or intuition?