46
JERALD J. BERNSTEIN
temporal projections from the retina to the tcctum. The nasal half of
the visual field (temporal half of the retina) was rcmoved from the visual
input. By using visual evoked responses the remaining area occupied
by the intact optic nerve fibers was mapped after scctioning the contralateral optic nerve. The area of the tectum which was deafferented by
optic nerve section diffcrcd only slightly in different experiments. Normal
evoked responses were obtained from the rostra1 portion of the tectum
with no response obtained from the deafferented caudal portion.
If the optic tract was cut and nerve fibers were not pcmiitted to
regenerate up either the lateral (nasal) or medial (temporal) divisions
of the optic tract, regenerating optic nerve fibers reestablished retinotectal projections which were similar to that shown in animals that had
previously undergone cutting of the divisions of the optic tract and
immediate recording (Jacobson and Gaze, 1965). This demonstrated a
retinotectal reestablishment of the original synaptic patterns upon the
neurons within the optic tectum. However, following nasal or temporal
hemisections and crushing of thc proximal optic nerve, there was significant departure from the normal course of ncrve fibers found within
the tectum. Such an operative procedure followed by regeneration resulted in the complete absence of sustained on and off responses which
werc localized in layer D (central gray) of the optic tectum (Jacobson
and Gaze, 1964). There was histological verification of this electrophysiological finding since there was an absence or near absence of ncrve
fibers in layer D of the tectum. It must be emphasized that retinotectal
regeneration was ncarly perfect and in all animals recovery was cxccdlent
except for the recovery of this one 1ayc.r. In another group of goldfish
the medial half of the optic tcctuni was removed and the left optic
nerve crushed (Jacobson and Gaze, 1964). Following regeneration, normal projcctions were restored to the lateral half of the tectum from thc
corresponding portion of the retinal visual field. Visual evoked responses
could be elicited in the normal retinotectal area of projection in the
tectum. In addition, stimulation of the visual field that normally projected to the medial half of the tectum did not result in visual cvokrd
responses in the remaining lateral portion of thc optic tectum. These
data show that optic nerve fibers dcstincd for the ablated half of thc
tectum fail to make connections whcreas a normal projection to the
intact half of the tcctum is reestablished.
These electrophysiological findings are dircct confirmation of the
anatomical study of Attardi and Sperry ( 1963). In addition, Jacobson
and Gaze (1965) have shown that thc regcmerating optic nerve fibers
do not go through as early a phase of sprcading out and thcn respecify-
JERALD J. BERNSTEIN
temporal projections from the retina to the tcctum. The nasal half of
the visual field (temporal half of the retina) was rcmoved from the visual
input. By using visual evoked responses the remaining area occupied
by the intact optic nerve fibers was mapped after scctioning the contralateral optic nerve. The area of the tectum which was deafferented by
optic nerve section diffcrcd only slightly in different experiments. Normal
evoked responses were obtained from the rostra1 portion of the tectum
with no response obtained from the deafferented caudal portion.
If the optic tract was cut and nerve fibers were not pcmiitted to
regenerate up either the lateral (nasal) or medial (temporal) divisions
of the optic tract, regenerating optic nerve fibers reestablished retinotectal projections which were similar to that shown in animals that had
previously undergone cutting of the divisions of the optic tract and
immediate recording (Jacobson and Gaze, 1965). This demonstrated a
retinotectal reestablishment of the original synaptic patterns upon the
neurons within the optic tectum. However, following nasal or temporal
hemisections and crushing of thc proximal optic nerve, there was significant departure from the normal course of ncrve fibers found within
the tectum. Such an operative procedure followed by regeneration resulted in the complete absence of sustained on and off responses which
werc localized in layer D (central gray) of the optic tectum (Jacobson
and Gaze, 1964). There was histological verification of this electrophysiological finding since there was an absence or near absence of ncrve
fibers in layer D of the tectum. It must be emphasized that retinotectal
regeneration was ncarly perfect and in all animals recovery was cxccdlent
except for the recovery of this one 1ayc.r. In another group of goldfish
the medial half of the optic tcctuni was removed and the left optic
nerve crushed (Jacobson and Gaze, 1964). Following regeneration, normal projcctions were restored to the lateral half of the tectum from thc
corresponding portion of the retinal visual field. Visual evoked responses
could be elicited in the normal retinotectal area of projection in the
tectum. In addition, stimulation of the visual field that normally projected to the medial half of the tectum did not result in visual cvokrd
responses in the remaining lateral portion of thc optic tectum. These
data show that optic nerve fibers dcstincd for the ablated half of thc
tectum fail to make connections whcreas a normal projection to the
intact half of the tcctum is reestablished.
These electrophysiological findings are dircct confirmation of the
anatomical study of Attardi and Sperry ( 1963). In addition, Jacobson
and Gaze (1965) have shown that thc regcmerating optic nerve fibers
do not go through as early a phase of sprcading out and thcn respecify-