The Animal Self: Neurobehavioral Correlates 159“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanitypatients with an amputated limb. It was reported that, in an experiment
in which the brain structure amygdala was electrically stimulated, a sen-
sation of nausea and belching was felt in the stomach, although no real
gastric movement could be detected.^30
7.12 Limitations Imposed by the Physical Brain
It is doubtful that the human brain will evolve into an ever more power-
ful thinking machine. Conventional wisdom says that the pelvic opening
of the mother imposes a limit to the size of the baby’s head. But even if
this difficulty is overcome (say, by routine caesarian section or by enlarg-
ing the cavity), basic physical laws provide an insurmountable constraint
to the structure of the neurons. The following are points to consider: (1)
Miniaturization of neurons can theoretically pack more cells per unit
volume. But, thermal vibration renders small-diameter axons inherently
unreliable for ion movement across membrane (the way action poten-
tials are made), reducing reliability of nerve signals. (2) Enlarging axonal
diameter can speed up nerve conduction, but the expenditure of energy
outpaces the gain in speed, rendering it cost-ineffective. (Current mam-
malian neurons have already gained speed by wrapping the axons with
myelin, an effective insulator.) (3) Enlarging the brain size can increase
neuron number, but this requires longer axons for longer-range trans-
mission of message, resulting in sluggish response to the environment,
as seen in elephants. Thus, improving the neuron-based intelligence hits
a roadblock. Fortunately, only humans, of all animals, break through the
barrier by inventing extracorporeal information-processing mechanisms,
such as language, writing, books, libraries, and, best of all, computers.^31
Notes and References
- Kety SS. (1960) A biologist examines the mind and behavior. Science 132:
1861–1870. - The speed of a good metallic conductor approaches that of light (3 × 10^8
meters per second).