44
JERALD J. BERNSTEIN
discrimination of light of differing intensity. Removal of one-half of the
cerebellum did not cause spatial orientation difficulty with visual or
acoustically oriented problems ( Bianki and Demina, 1964). These results
are interesting since removal of the optic tectum on one side results in
the animal's being blind on that side and untrainable to photic stimulation (Karamyan, 1957).
In addition, it has been found (Arora, 1962) that the engram or
memory trace is acquired bilaterally in the fish. Therefore, training one
eye and removing the optic tectum contralateral to the trained eye did
not affect the ability of an animal to respond appropriately by utilizing
the naive untrained eye and the remaining tectal input.
G. Retinotopic Respecification of the Regenerated Optic Nerve
The regeneration of the optic nerve into the optic tectum of the
goldfish as well as other species of fish has been demonstrated (Healey,
1957). Recent experiments have been carried out on the goldfish and
cichlid Astronotus ocellatus. Ten to 12 days after section of the optic
nerve, regenerating axons began to reinnervate the tectal hemispheres
from the medial and lateral optic tracts (Attardi and Sperry, 1963). In
14-18 days, the regenerating nerve fibers entered the plexiform layer
of the optic tectum. This coincided with the onset of the recovery of
vision. At this time all the new reinnervating nerve fibers were unmyelinated. During the following weeks the nerve fibers underwent a slow
process of maturation and increased in diameter with a concomitant
deposition of myelin. The representation of the retina on the optic tectum
is upside down and backwards in comparison with the retinal projection
( Attardi and Sperry, 1963; Brett, 1957; Healey, 1957). When the dorsal
half of the retina was removed and the optic nerve of the same side
severed, the regenerating nerve fibers in the optic nerve could originate
only from ganglion cells in the ventral half of the retina (Attardi and
Sperry, 1963). The regenerating nerve fibers were found to enter their
original tract, the medial bundle of the optic tract. With few exceptions
the lateral bundle was completely without nerve fibers following regeneration of the transected optic nerve. The nerve fibers were parallel
within the medial tract and only entered the plexiform layers in the
dorsal tectum. Conversely, if the ventral half of the retina was removed
prior to nerve transection nearly all of the regenerated nerve fibers were
found to enter only the lateral bundle and to innervate only the ventral
half of the tectal hemisphere. In a series of elegant experiments it was
shown that peripheral, central, dorsal, and ventral optic nerve fibers
JERALD J. BERNSTEIN
discrimination of light of differing intensity. Removal of one-half of the
cerebellum did not cause spatial orientation difficulty with visual or
acoustically oriented problems ( Bianki and Demina, 1964). These results
are interesting since removal of the optic tectum on one side results in
the animal's being blind on that side and untrainable to photic stimulation (Karamyan, 1957).
In addition, it has been found (Arora, 1962) that the engram or
memory trace is acquired bilaterally in the fish. Therefore, training one
eye and removing the optic tectum contralateral to the trained eye did
not affect the ability of an animal to respond appropriately by utilizing
the naive untrained eye and the remaining tectal input.
G. Retinotopic Respecification of the Regenerated Optic Nerve
The regeneration of the optic nerve into the optic tectum of the
goldfish as well as other species of fish has been demonstrated (Healey,
1957). Recent experiments have been carried out on the goldfish and
cichlid Astronotus ocellatus. Ten to 12 days after section of the optic
nerve, regenerating axons began to reinnervate the tectal hemispheres
from the medial and lateral optic tracts (Attardi and Sperry, 1963). In
14-18 days, the regenerating nerve fibers entered the plexiform layer
of the optic tectum. This coincided with the onset of the recovery of
vision. At this time all the new reinnervating nerve fibers were unmyelinated. During the following weeks the nerve fibers underwent a slow
process of maturation and increased in diameter with a concomitant
deposition of myelin. The representation of the retina on the optic tectum
is upside down and backwards in comparison with the retinal projection
( Attardi and Sperry, 1963; Brett, 1957; Healey, 1957). When the dorsal
half of the retina was removed and the optic nerve of the same side
severed, the regenerating nerve fibers in the optic nerve could originate
only from ganglion cells in the ventral half of the retina (Attardi and
Sperry, 1963). The regenerating nerve fibers were found to enter their
original tract, the medial bundle of the optic tract. With few exceptions
the lateral bundle was completely without nerve fibers following regeneration of the transected optic nerve. The nerve fibers were parallel
within the medial tract and only entered the plexiform layers in the
dorsal tectum. Conversely, if the ventral half of the retina was removed
prior to nerve transection nearly all of the regenerated nerve fibers were
found to enter only the lateral bundle and to innervate only the ventral
half of the tectal hemisphere. In a series of elegant experiments it was
shown that peripheral, central, dorsal, and ventral optic nerve fibers