Ordinary Cats Research Articles

The contribution of the corpus callosum to receptive fields in the lateral suprasylvian visual areas of the cat

In both ordinary cats and ‘Boston’ Siamese cats the visual areas in the lateral parts of the middle and posterior suprasylvian gyri (LSA) contain an extensive representation of the ipsilateral half of the visual field. In addition, in both groups of cats the overwhelming majority of neurons in LSA can be driven from both eyes. In Siamese cats this binocular interaction is in marked contrast with what is found in area 17 where neurons are almost exclusively activated through the contralateral eye. Transection of the posterior 1 3 to 1 2 of the corpus callosum had a different effect on the physiological organization of LSA in the two types of cats. In ordinary cats it caused the loss of the ipsilateral hemifield representation in the eye ipsilateral to the side of recording and reduced this representation in the other eye. However, after the section of the corpus callosum LSA neurons remained binocular. In Siamese cats the callosal transection left the representation of the ipsilateral hemifield in LSA unaffected, but totally abolished the input from the ipsilateral eye. These findings suggest that the visual callosal input to LSA has a different functional significance in ordinary and Siamese cats. In the former cats it may be related to perceptual equivalence across the vertical meridian of the visual field, whereas in the latter cats it may subserve interocular equivalence.

Histochemical studies on the inferior oblique muscle of Siamese cats and domestic cats with unilateral lid suture

Eye muscles of Siamese cats and monocularly lid sutured domestic cats have been shown to contract slower and fatigue quicker than eye muscles of normal domestic cats. The structural correlates to these functional differences were explored with histochemical techniques in the same muscles that were studied physiologically. Sections were stained for myosine ATPase and succinic dehydrogenese (SDH). The muscles of Siamese cats were smaller in cross-sectional area than muscles of ordinary cats. The proportions of type I, and type II and II C fibers were the same in all animals. In Siamese cats fibers of all types, and in domestic lid sutured animals type II fibers were smaller than corresponding types in normal cats. No differences could be detected between animals with respect to SDH staining properties. The capillary density per fiber was significantly lower in lid sutured domestic cats and Siamese cats than in normal cats. These changes in muscle and fiber area, and in capillary density are probably the morphological correlates to the observed functional differences. It has been suggested that they are related to deficiencies in visual function, particularly in binocular vision; they might represent muscular adaptation to reduced demands for fusional vergence movements in Siamese and lid sutured domestic cats, and for saccadic activity in Siamese cats.

Behavioral and electrophysiological effects of unilateral optic tract section in ordinary and siamese cats

In ordinary cats, section of one optic tract produced a complete contralateral hemianopsia in both eyes. Single-unit recordings showed a normal representation of the contralateral nasal retina and ipsilateral temporal retina in the SC on the side of the intact optic tract. In addition, in the rostral portion of this SC there was a representation of a small portion of the contralateral temporal retina. This portion was apposed to the vertical meridian and its width was at most 6 degrees. In the anterior half of the SC on the side of the optic tract section, despite the interruption of any direct optic input, there was an extensive representation of the ipsilateral nasal retina and the contralateral temporal retina. This indirect visual input to the SC ipsilateral to the optic tract section was absent in a cat with a section of the forebrain commissures. In Boston Siamese cats, section of one optic tract led to a virtually complete blindness in the eye contralateral to the section, whereas the other eye retained a full visual field, although the responsiveness of the temporal retina beyond 20 degrees from the vertical meridian was reduced. Similarly, the nasal hemiretina and most of the temporal hemiretina on the side of the section were represented in the opposite SC, whereas stimulation of the eye contralateral to the section could not drive SC units. There was some evidence that the visual field of the eye on the side of the section could at least in part be represented in the SC on the same side. The findings indicate that the crossed projections from temporal hemiretina in the ordinary cat, and the uncrossed projections from temporal hemiretina in the Siamese cat are insufficient by themselves to sustain visual orientation and to drive SC neurons. Each half of the visual field in the ordinary cat, and the field of each eye in the Siamese cat, can be represented in the ipsilateral SC via across-the-midline, indirect connections.

Siamese cats: abnormal responses of retinal ganglion cells.

Comparison of optic tract recordings in Siamese and ordinary cats reveals that Siamese cats have a significantly lower percentage of Y-cells than of X-cells. In addition, Siamese cats show depressed responses to a contrast-reversal stimulus, a result that supports the lower spatial contrast sensitivity demonstrated behaviorally by these animals. Both physiological findings suggest neurophysiological anomalies in the Siamese retina.

Temporal aspects of spatial vision in the cat

Using behavioral techniques, contrast sensitivity for flickering and stationary gratings was measured in ordinary cats. Gratings of low spatial frequency were more easily detected by the cat when temporal modulation was present, but at high spatial frequencies temporal modulation reduced grating visibility. These psychophysical results are consistent with neurophysiological evidence for the existence of two classes of visual cells in the cat, which are distinguishable in terms of their spatio-temporal response properties.

Abnormal Visual Resolution in the Siamese Cat

When tested behaviorally, Siamese cats display marked differences in contrast sensitivity compared to ordinary cats. Overall sensitivity is depressed, the high-frequency cutoff point is lower, and there is less falloff in sensitivity at low spatial frequencies. Optical factors may contribute to these differences, or they may be attributable to the well-established anatomical abnormalities within the visual system of the Siamese cat.

Aberrant visual projections in the Siamese cat.

Aberrant visual projections in the Siamese cat.

Manx Cats

WITH reference to Mr. Francis Galton's remarks in NATURE on Manx cats, I should like to ask whether any of your readers can assist me. Some little time ago I imported a few Manx cats with a view of trying experiments with them in crossing. But, as Mr. Galton says, it is difficult to get cats to breed in confinement, and of course it is of no use for the purpose of my experiment to allow the animals to roam at large among ordinary cats. Acting upon Mr. Gallon's suggestion, therefore, I write to ask whether any of your readers happen to know of any island within a reasonable distance from town where a breed of Manx cats could be established. It is not necessary that the island should be a marine one. Any piece of ground insulated by fresh water would do equally well, provided it were of moderate size and not already tenanted by cats. If any of your readers should know of such a place I should be greatly obliged to them for a reference to its locality.