34
JERALD J. BERNSTEIN
possess profusely branched apical dendrites and no basal tuft of dendrites
(Ramon y CajB1, 1952). These primitive nerve cells may be one of the
cell types which are responsible for the regeneration of the optic tectum
(Ramon y CajBl, 1952). The optic trctum of the teleost, because of its
rich afferent and efferent conncctions, appears to be the major center for
the integration of visual information with other sensory modalities and
the integration center for exteroceptive information ascending and descending from other neural centers.
B. Spontaneous Activity of the Optic Tectum
Electroencephalograms recorded from the optic tectum of codfish,
Gadus callarias, have indicated the existence of a thalamic and mesencephalic reticular activating system ( Enger, 1957). The dominant frequency of both tectum and forebrain in dark-adapted animals was 8-13
Hz. The optic tectum signal had a component that resembled the
spindling of mammalian alpha rhythm. Arousal was initiated by general
illumination and acoustic stimulation and resulted in a dominant rhythm
of 18-32 Hz. The goldfish optic tectum had a dominant rhythm of 7-14
Hz which increased in frequency to 18-24 Hz (arousal) after photic
stimulation ( SchadC, 1959; SchadC and Weiler, 1959).
C. Electrophysiological Characteristics of the Visual Input
There have been extensive mappings of the retinotectal characteristics
of the visual input in cyclostomes, plagiostomes, and actinopterygians. In
the lamprey, Lampetra fluuiatilis, illumination of the eye resulted in
visually evoked responses in the optic tectum, tegmentum, medulla
oblongata, and spinal cord (Karamian et al., 1966). These responses
were elicited by stimulation of the lateral as well as parietal eye. Stimulation of the parietal eye elicited a slow negative wave with a 100-150msec latency. Stimulation of the lateral eye elicited a series of slow
oscillations initiated after 60-90 msec as a negative or negative-positive
wave of maximal amplitude. The neural units within the tectum of the
lamprey were quite susceptible to fatigue even at low frequencies of
stimulation (one light flash per 20-30 sec). Flashes at intervals of 2-5
sec were followed by a marked decrease in the amplitude of the first
wave. This demonstrated that the primary wave of the visually evoked
response of the lamprey was the discharge of retinal “on units”; subsequent oscillations were related to discharges of retinal “off units.” The
visual evoked response in the lamprey was comprised of two com-
JERALD J. BERNSTEIN
possess profusely branched apical dendrites and no basal tuft of dendrites
(Ramon y CajB1, 1952). These primitive nerve cells may be one of the
cell types which are responsible for the regeneration of the optic tectum
(Ramon y CajBl, 1952). The optic trctum of the teleost, because of its
rich afferent and efferent conncctions, appears to be the major center for
the integration of visual information with other sensory modalities and
the integration center for exteroceptive information ascending and descending from other neural centers.
B. Spontaneous Activity of the Optic Tectum
Electroencephalograms recorded from the optic tectum of codfish,
Gadus callarias, have indicated the existence of a thalamic and mesencephalic reticular activating system ( Enger, 1957). The dominant frequency of both tectum and forebrain in dark-adapted animals was 8-13
Hz. The optic tectum signal had a component that resembled the
spindling of mammalian alpha rhythm. Arousal was initiated by general
illumination and acoustic stimulation and resulted in a dominant rhythm
of 18-32 Hz. The goldfish optic tectum had a dominant rhythm of 7-14
Hz which increased in frequency to 18-24 Hz (arousal) after photic
stimulation ( SchadC, 1959; SchadC and Weiler, 1959).
C. Electrophysiological Characteristics of the Visual Input
There have been extensive mappings of the retinotectal characteristics
of the visual input in cyclostomes, plagiostomes, and actinopterygians. In
the lamprey, Lampetra fluuiatilis, illumination of the eye resulted in
visually evoked responses in the optic tectum, tegmentum, medulla
oblongata, and spinal cord (Karamian et al., 1966). These responses
were elicited by stimulation of the lateral as well as parietal eye. Stimulation of the parietal eye elicited a slow negative wave with a 100-150msec latency. Stimulation of the lateral eye elicited a series of slow
oscillations initiated after 60-90 msec as a negative or negative-positive
wave of maximal amplitude. The neural units within the tectum of the
lamprey were quite susceptible to fatigue even at low frequencies of
stimulation (one light flash per 20-30 sec). Flashes at intervals of 2-5
sec were followed by a marked decrease in the amplitude of the first
wave. This demonstrated that the primary wave of the visually evoked
response of the lamprey was the discharge of retinal “on units”; subsequent oscillations were related to discharges of retinal “off units.” The
visual evoked response in the lamprey was comprised of two com-