1. ANATOMY AND PHYSIOLOGY O F THE CENTRAL NERVOUS SYSTEM
47
ing in a maturation process such as is found in amphibia (Gaze et al.,
1963, 1965a ) but establish original retinotectal connections immediately
upon entry into the tectum.
Not only does it appear that regeneration of the nerve into the tectum
is specific but excision and reimplantation of a tectal flap with a normal
orientation resulted in the restitution of the normal visual projections
over the arm of the graft (Gaze et al., 1965b). However, restoration of
the visually evoked retinal map on the tectal surface was not accompanied by restoration of the normal sequence of visual responses throughout the entire depth of the excised and reimplanted optic tectum.
Following regeneration of the optic nerve, fish can make a hue
discrimination ( Arora and Sperry, 1963). Astronotus ocellatus were
trained to jump out of water to two different color stimuli for food
reward. Red, blue, grcen, and yellow were the colored stimuli which
wcre controlled for brightness. Following optic nerve crush and regeneration, previously trained fish were still able to make a hue discrimination. This demonstrates that regeneration of the optic nerve results in
retention of perception of the same quality of hue by the animal ( Arora
and Sperry, 1963).
Pattern vision appears to be restored following optic nerve regeneration since fish respond appropriately in an optokinetic drum (Healey,
1957) and the return of visual responses to moving objects has been
demonstrated electrophysiologically (Jacobson and Gaze, 1964 ) ; however, critical testing is necessary to establish the degree of functional
return of pattern vision. Panels of dots of progressively reduced intervals
were used as a measure of visual acuity and visual angle ( Weiler, 1966).
The average value of visual'acuity in the normal eye of Astronotus is 5.3
min of visual angle, Since it was found that the mean diameter of unfixed
cones in the retina is 2 . 9 2 ~ a single cone appears to correspond to
5 min of visual angle. Thus, the actual cone dimensions were close to
the predicted value and in the upper limits of the visual acuity measured. In all cases there was regeneration of the severed optic nerve
and return of vision. The average percentage of the restoration of acuity
w ; ~
78% of normal. In another group of animals the fish were trained
to discriminate betwcen a uniform dot pattern and a pattern of randomly
arranged dots of various sizes. The learning curves of these animals did
not differ significantly from normals. This was a gross indication that the
regener'ition and restoration of central connections was uniform and
probably distributed evenly over the areas of the tectum. It is interesting
that the high degrce of recovery found by Weiler (1966), which he
suggests under ideal conditions can approach 100% can occur when a
47
ing in a maturation process such as is found in amphibia (Gaze et al.,
1963, 1965a ) but establish original retinotectal connections immediately
upon entry into the tectum.
Not only does it appear that regeneration of the nerve into the tectum
is specific but excision and reimplantation of a tectal flap with a normal
orientation resulted in the restitution of the normal visual projections
over the arm of the graft (Gaze et al., 1965b). However, restoration of
the visually evoked retinal map on the tectal surface was not accompanied by restoration of the normal sequence of visual responses throughout the entire depth of the excised and reimplanted optic tectum.
Following regeneration of the optic nerve, fish can make a hue
discrimination ( Arora and Sperry, 1963). Astronotus ocellatus were
trained to jump out of water to two different color stimuli for food
reward. Red, blue, grcen, and yellow were the colored stimuli which
wcre controlled for brightness. Following optic nerve crush and regeneration, previously trained fish were still able to make a hue discrimination. This demonstrates that regeneration of the optic nerve results in
retention of perception of the same quality of hue by the animal ( Arora
and Sperry, 1963).
Pattern vision appears to be restored following optic nerve regeneration since fish respond appropriately in an optokinetic drum (Healey,
1957) and the return of visual responses to moving objects has been
demonstrated electrophysiologically (Jacobson and Gaze, 1964 ) ; however, critical testing is necessary to establish the degree of functional
return of pattern vision. Panels of dots of progressively reduced intervals
were used as a measure of visual acuity and visual angle ( Weiler, 1966).
The average value of visual'acuity in the normal eye of Astronotus is 5.3
min of visual angle, Since it was found that the mean diameter of unfixed
cones in the retina is 2 . 9 2 ~ a single cone appears to correspond to
5 min of visual angle. Thus, the actual cone dimensions were close to
the predicted value and in the upper limits of the visual acuity measured. In all cases there was regeneration of the severed optic nerve
and return of vision. The average percentage of the restoration of acuity
w ; ~
78% of normal. In another group of animals the fish were trained
to discriminate betwcen a uniform dot pattern and a pattern of randomly
arranged dots of various sizes. The learning curves of these animals did
not differ significantly from normals. This was a gross indication that the
regener'ition and restoration of central connections was uniform and
probably distributed evenly over the areas of the tectum. It is interesting
that the high degrce of recovery found by Weiler (1966), which he
suggests under ideal conditions can approach 100% can occur when a