Biology Reference
In-Depth Information
7
Investigations of H. K. Hartline
and S. W. Kuffler
Newton (
1675
) had rightly presumed that light signals were
transformed in the retina, and that the information about the visual
world was conveyed to the brain by the optic nerve. His suggestion
that visual information was transmitted by a vibration code,
however, proved to be wrong. Thus, early in the twentieth century it
had become generally accepted that the optic nerve fibres reacted to
light by discharging a series of brief electrical action potentials. With
increasing light intensity, the fibres tended to increase their firing
rate, but the size of the discharge remained constant. (For a review
of how our knowledge about the electrical nature of nerve impulses
emerged, see Boring,
1957
, pp. 30, 39-43 and Granit,
1947
.)
7.1 T h e e l e c t r i c a l r e s p o n s e s t o l i g h t
stimuli in single optic nerve fibres
H. K. Hartline was the first to make a thorough investigation of the
electrical responses to light stimuli in single optic nerve fibres. A
small bundle of fibres dissected from the optic nerve was split succes-
sively until only a single fibre remained. Thereafter, the electrical
activity of the fibre, generated by a light stimulus, was recorded by
means of an oscillograph capable of registering small, rapid voltage
fluctuations. The recordings were made under conditions where the
eye was illuminated by light of various intensities, durations and
wavelengths (see Hartline,
1940,
for a review).
7.2 The electrical responses in single
optic nerve fibres of
Limulus
In the retina of
Limulus
(horseshoe crab), where each photoreceptor is
directly linked with a separate nerve fibre, Hartline found that a brief
