W. Riss

THE OPTIC TRACTS OF RANA PIPIENS1

In man, the retina is known to establish important connections with the diencephalon and mesencephalon. A study of the emergence of these connections in lower forms should provide valuable information on the development and evolution of these brain stem regions. Towards this end studies on the visual system of lower vertebrates are presently a concern of this laboratory. A study on the optic system of a urodele has already been presented (Riss et al. 1963) and work on a reptile is in progress. The present paper describes the optic system of an anuran, Rana pipiens. Two different versions of the optic connections of Anura have been reported in the literature. One version (Bellonci 1888 and Wlassak 1893) described optic fibers traversing the diencephalon but terminating almost exclusively in the midbrain. The othcr viewpoint, favored by Gaupp (1899) and Herrick (1925), described the optic pathways of Anura as terminating profusely in the thalamus as well as the midbrain. Bellonci ( 1888) published one of the earliest comparative investigations on the visual system of vertebrates using normal material. His study included many different species of tailed and tailless amphibians. In the thalamus of Anura (in addition to the corporis geniculati thalami of earlier authors), he reported two hitherto undescribed areas of neuropil which are now prominently associated with optic fibers. One area of neuropil found in the anterior thalamus, dorsal to the corporis geniculati thalami, was named the anterior superior nucleus of the corporis geniculati thalami. This area was later renamed by Herrick (1925, p. 454), the nucleus of Bellonci, and still later (Herrick 1933), the neuropil of the nucleus of Bellonci. The second area of neuropil was situated in the caudal thalamus and was called, by Bellonci, the posterior

Tail Pinch-Induced Arousal and Stimulus-Bound Behavior in Rats with Lateral Hypothalamic Lesions

Arousal induced by tail pinching results in stimulus-bound feeding, licking and gnawing in male rats during the aphagic and adipsic phase that follows electrolytic damage to the lateral hypothalamus (LH). Such stimulus-bound behavior is very similar to electrically induced stimulus-bound behavior. Furthermore, brain-damaged animals during tail pinch-induced drinking trials are responsive to the sensory properties of the test liquid. Chocolate milk is consumed but tap water is actively rejected. Tail pinch to sham-operated control rats failed to induce such behavior; instead, it induced rage behavior towards the hand that pinched the tail. The results support the conclusion that rats with LH lesions require an arousing stimulus for feeding but that the same externally applied arousing stimulus enhances active rejection of tap water.

ANATOMICAL ASPECTS OF THE EVOLUTION OF THE LIMBIC AND OLFACTORY SYSTEMS AND THEIR POTENTIAL SIGNIFICANCE FOR BEHAVIOR

It is our intention in this presentation to review briefly the history of thought concerning the limbic structures or rhinencephalon. Following the brief review, the anatomical connections of the limbic system and the olfactory system in vertebrates will be described. The basic pattern of connections as seen in mammals, amphibia and the lamprey will be emphasized. Finally, the significance of the connections will be considered. In general, we may anticipate that the connections we will describe support our view that the olfactory system evolved from the limbic system rather than the traditional views that the limbic system is either separable from the olfactory system or evolved from the olfactory system. Moreover, the limbic system will be described in theoretical terms as a system which is responsive to the internal milieu, whereas the olfactory system, a derivative of the limbic system, is responsive to the external chemical milieu.

Levels of Function and their Representation in the Vertebrate Thalamus

A reptile has been found with corticaldevelopment intermediate between that of other reptiles and that of mammals. The reptile, a side-necked turtle, shows evidence of considerably more corticothalami

Retinal Projections in the Tiger Salamander, Ambystoma tigrinum; pp. 425–442

Degenerating retinofugal fibers and their terminal fields have been examined in the tiger salamander, Ambystoma tigrinum. The crossed pathway includes: (1) A large bundle which cont

Testing a Theory of Brain Function by Computer Methods

Using a personal computer as a tool, methods of studying the time course and sequencing of human brain processes are described. Reasons are given for choosing the visual system and brain control of eye movement as the input-output model for tracing the processes. With such a model it is possible to study the spectrum of functions from initial input processes to higher level controls often attributed to the prefrontal cortex. The testing technique was devised for use in relation to a unified theory of brain processing but it is a useful approach to functional assessment regardless of the particular theory being evaluated.

Overview of the Design of the Central Nervous System and the Problem of the Natural Units of Behavior

An illustration is given of how the three major forms of vertebrate locomotion may be understood. It is suggested that swimming by lateral undulations, jumping and quadrupedal progression can be produced through the very same spinal cord design and vestibular organization. All three forms of locomotion are described in terms of waves of neuronal activity dependent on the stretch and tension of trunk musculature. Musculature of the right and left half of the body are antagonistic in swimming by lateral undulations; musculature of the dorsal and ventral trunk are antagonistic in jumping locomotion; and musculature of the right dorsal and left ventral compartments are antagonistic to the left dorsal and right ventral compartments during the twisting action of quadrupedal progression. It is emphasized that no changes in spinal or vestibular action are needed to accommodate any form of locomotion. Only differences in proprioceptive input are required. An initial statement is given of the relation between basic vestibular reflexes and the forms of locomotion. It is obvious that the locomotor rhythms are consistent with basic spinal as well as vestibular reflexes.