D.I. Hamasaki

Properties of the parietal eye of the green iguana.

Abstract The ERG evoked by achromate stimuli was used to study the properties of the parietal eye of the Green Iguana. The response consisted of a positive component (positive on-response and a negative off-response), and a negative component (negative on-response and no response at off) which were independent and had different properties. The negative component was more sensitive and had a long refractory period whereas the positive component had a higher threshold but had a very short refractory period. The parietal eye of the iguana studied had properties which were more like those of the lateral eyes of nocturnal reptiles (gecko and caiman) than those of its own lateral eye.

Temporal characteristics of peripheral inhibition of sustained and transient ganglion cells in cat retina

Abstract The temporal characteristics of transient and sustained retinal ganglion cells in the cat were assessed by varying the temporal relationship between a spot in the receptive field center and an annulus in the receptive field surround. The luminance of the annulus was also varied for some units. The maximum amount of suppression of the excitatory response from the center spot was produced when the annulus preceded the spot by about 38 msec for transient cells and by about 7 msec for sustained cells. The time course of peripheral inhibition for transient and sustained cells was also found to differ. These differences held at all luminance levels used but were minimized at both extremely low and extremely high contrast levels.

Spectral sensitivity of the parietal eye of the green iguana

Abstract The slow photic response of the parietal eye of the Green Iguana consisted of a positive and negative component which were wave-length dependent. The spectral sensitivity curve of the positive component peaked at 460 nm while that of the negative component at 520 nm. The two components responded differently to double flashes; the amplitude of the negative component elicited by a second 560 nm stimulus decreased as the inter-flash interval was decreased while that of the positive component elicited by a 440 nm stimulus increased as the inter-flash interval decreased. The positive component appeared to be a pre-excitatory inhibitory system.

The erg-determined spectral sensitivity of the octopus

The ERG-determined scotopic spectral sensitivity curve of the intact, anesthetized octopus was a broad curve which peaked at 480 nm with no secondary peaks. Adaptation to white light resulted in a narrowing of the curve but the λmax remained at 480 nm. Adaptation to blue, green or red light did not induce a shift in the λmax but resulted in a depression and narrowing of the sensitivity curve. Because of the absence of a Purkinje shift and the narrowing of the sensitivity curve following light-adaptation, it was concluded that the broadness of the sensitivity curve was due to a high effective retinal density of the photopigment and that only one system was present in the retina of the octopus.

The electroretinogram of the intact anesthetized octopus

Abstract The ERG recorded from the urethanized octopus consisted of a sustained negative wave which resembled somewhat the receptor potential of the arthropods and also the P111 component and the late receptor potential of the vertebrates. Superimposed on the negative wave were fast oscillations whose latency, frequency and modulation varied with stimulus intensity and state of adaptation. There was a smooth increase in sensitivity of 3.5 log units during 60 min of darkness and two-thirds of this was attained in the first 11 min. The flicker fusion frequencies were significantly lower than those of the “fast” eyes of the arthropods and comparable to those of the diurnal vertebrates. Arousal of the lightly anesthetized octopus did not alter the ERG.

The electroretinogram of the iguana and Tokay gecko.

Abstract Using the electroretinogram as the criterion of retinal activity, dark-adaptation, CFF, suppression, and hypothermia were investigated in the Iguana iguana and Gekko gekko . The ERGs of both species display properties of a simplex type of retinal organization, with that of the iguana being consistent with a pure cone retina and that of the gecko consistent with a pure rod retina. The degree of suppression was significantly greater in the gecko than the iguana. During hypothermia there was a progressive decrease in the size of all components of the ERG, but all components were present even at 5°.

Response of cat retinal ganglion cell to moving stimuli

Abstract Responses elicited from cat retinal ganglion cells by moving stimuli of different intensities and heights were studied. Two types of response patterns were recorded: in type I cells, there was a decrease in the firing rate when the stimulus entered the periphery; in type II cells, there was no indication of the inhibition from the periphery. Evidence was presented that these correspond to the sustained and transient units reported by other investigators. Changes in the stimulus intensity and height did not change the measured size of the receptive field center which indicated that the center and surround components of the receptive field are changing proportionately.

Comparison of LGN and optic tract intensity-response functions.

Abstract Single cell recordings were made from cat lateral geniculate (LGN) neurons while varying the luminance and size of spots flashed in the center of their receptive fields. The major purpose of the study was to describe any transformations of luminance information that occur in the lateral geniculate. Therefore, comparisons were made between the data recorded and previously published data ( Winters and Walters, 1970 ) from single optic tract neurons, obtained under similar stimulus conditions. The on center LGN neurons showed 2 components in their neuronal discharge patterns that were not found in optic tract fibres. First, at intensities near threshold, at the termination of the stimulus there is a long period, lasting for about 300 msec, in which there is complete suppression of neural activity. This silent period is often followed by a brief discharge before the unit returns to its spontaneous level of firing. Second, at intensities greater than 1.4 log units above threshold, there is a brief period after the on transient, in which there is complete suppression of the response. This silent period lasts about 30 msec and is followed by a relatively depressed steady state component. LGN off center cell response patterns were not found to differ from those of optic tract units. Quantitative evidence for these findings is given.

Spatial organization of normal and visually deprived units in the lateral geniculate nucleus of the cat

Abstract The spatial organization of the receptive fields of lateral geniculate neurons of cats was examined by single unit techniques. The stimulus consisted of spots of various sizes centered on the receptive field center. Of the 62 units examined, 24 received input from the normal eye and 38 from the visually deprived eye. The visually deprived units had small receptive field centers and antagonistic center-surround organization. Examination of peristimulus time histograms showed that approximately 50 per cent of the units fed by the visually deprived eye had firing patterns consistently different from the units innervated by the normal eye. These units had symmetrical firing patterns which did not change with increasing stimulus diameters, low maximum firing rate and long latency. Calculation of the summation of inhibition in the peripheral portion of the receptive field showed that these units had stronger inhibition than the normal units.

Depression of the late receptor potential and the ERG by light deprivation in cats

Abstract The ERG and late receptor potentials were recorded from normal and light-deprived eyes of cats. Light deprivation was accomplished by suturing the lids of one eye closed shortly after birth, and the cats were tested after at least 6 months of light deprivation. Both the late receptor potential and the ERG were significantly smaller in the light-deprived eyes. The degree of depression varied considerably between animals which is probably due to the variation in the amount of light flux eliminated by lid closure. No difference between the two eyes could be detected 8 weeks after the previously closed eye was opened. A hypothesis regarding the physiological basis for the depression is presented.