1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
35
ponents, a fast component which appeared to be related to the presynaptic fibers of the retinal ganglionic cells and a slow component
which was a negative or a positive-negative wave and evidently represented the dendritic potentials of radially oriented optic tectal units. The
occurrence of a single wave in response to light stimulation warranted the
assumption that, in contrast to teleost fish which have a bimodal (Konishi,
1960) or trimodal fiber spectrum (Dawson and Bernstein, 1970), the
optic nerve of the lamprey consists of nerve fibers with uniform conduction velocity and therefore a unimodal fiber spectrum (Karamian et al.,
1966). In addition to this finding, visual evoked responses resulted in
discharges in the medulla and the spinal cord, although no responses
were recorded from the telencephalon. The response in the medulla and
spinal cord appeared to be due to discharges of Muller’s fibers. The
h4uller neurons in the lamprey aggregate and form the tegmental motor
nucleus. The response recorded from the Muller fibers in the spinal cord
were of the same latency as the response recorded from the optic tectum.
Ablation of the optic tectum did not affect the afferent visual input to the
h$uller cells; therefore, the visual input was derived from another pathway of the primary afferent optic nerve fibcrs (Karamian et al., 1966).
Evoked visual responses could be recorded from the optic tectum of
the plagiostonies Raja and Trygon following stimulation of the eye by
light or electrical stimulation of the optic nerve (Karamian et al., 1966).
The latency of the response in the contralateral optic tectum was 50-60
msec. Direct stimulation of the optic nerve resulted in a slow negativepositive wavc with a latency of 6.0 msec. Oscillations did not precede
this slow optic tectal response. The slow wave of the optic tectal response
of these skates showed neither double nor accessory peak which indicated that the skate like the lamprey has a unimodal distribution of
nerve fiber diameter in the optic nerve (Karamian et al., 1966).
The visual evoked response in the optic tectum has been studied in
the teleosts (goldfish, bass, carp, and bluegill) using perinietry. The
stimuli were small spots of light which subtend angles of 0.5”, lo, 2” up
to 30”, as well as small circular disks placed on a background that
encompassed the visual field (Fig. 5 ) . The three superficial tectal layers
of primary afferent optic fibers terminated on cells which had the same
characteristic responses to the visual field as neural units found within
the retina (Jacobson and Gaze, 1964; MacNichol et al., 1961; Schwassman and Kruger, 1965; Wagner et al., 1963). The retinotectal projection
of retinal units recorded from the upper three zones of the tectum
demonstrate tcctal neurons with threcx types of responses (Jacobson and
Gaze, 1964). These responses can be classified as units which are “on,”
“off,” or “on-off .” Units with on centers can be subdivided according to
35
ponents, a fast component which appeared to be related to the presynaptic fibers of the retinal ganglionic cells and a slow component
which was a negative or a positive-negative wave and evidently represented the dendritic potentials of radially oriented optic tectal units. The
occurrence of a single wave in response to light stimulation warranted the
assumption that, in contrast to teleost fish which have a bimodal (Konishi,
1960) or trimodal fiber spectrum (Dawson and Bernstein, 1970), the
optic nerve of the lamprey consists of nerve fibers with uniform conduction velocity and therefore a unimodal fiber spectrum (Karamian et al.,
1966). In addition to this finding, visual evoked responses resulted in
discharges in the medulla and the spinal cord, although no responses
were recorded from the telencephalon. The response in the medulla and
spinal cord appeared to be due to discharges of Muller’s fibers. The
h4uller neurons in the lamprey aggregate and form the tegmental motor
nucleus. The response recorded from the Muller fibers in the spinal cord
were of the same latency as the response recorded from the optic tectum.
Ablation of the optic tectum did not affect the afferent visual input to the
h$uller cells; therefore, the visual input was derived from another pathway of the primary afferent optic nerve fibcrs (Karamian et al., 1966).
Evoked visual responses could be recorded from the optic tectum of
the plagiostonies Raja and Trygon following stimulation of the eye by
light or electrical stimulation of the optic nerve (Karamian et al., 1966).
The latency of the response in the contralateral optic tectum was 50-60
msec. Direct stimulation of the optic nerve resulted in a slow negativepositive wavc with a latency of 6.0 msec. Oscillations did not precede
this slow optic tectal response. The slow wave of the optic tectal response
of these skates showed neither double nor accessory peak which indicated that the skate like the lamprey has a unimodal distribution of
nerve fiber diameter in the optic nerve (Karamian et al., 1966).
The visual evoked response in the optic tectum has been studied in
the teleosts (goldfish, bass, carp, and bluegill) using perinietry. The
stimuli were small spots of light which subtend angles of 0.5”, lo, 2” up
to 30”, as well as small circular disks placed on a background that
encompassed the visual field (Fig. 5 ) . The three superficial tectal layers
of primary afferent optic fibers terminated on cells which had the same
characteristic responses to the visual field as neural units found within
the retina (Jacobson and Gaze, 1964; MacNichol et al., 1961; Schwassman and Kruger, 1965; Wagner et al., 1963). The retinotectal projection
of retinal units recorded from the upper three zones of the tectum
demonstrate tcctal neurons with threcx types of responses (Jacobson and
Gaze, 1964). These responses can be classified as units which are “on,”
“off,” or “on-off .” Units with on centers can be subdivided according to