AVOIDANCE BEHAVIOR OF RAT

If wild rats in human communities behaved as tamed ones do toward unfamiliar objects, their compulsive exploratory and sampling behavior would probably lead them into traps or result in the ingestion of poison bait. Neophobia , displayed in highly developed form by wild rats, protects them from the consequences of curiosity. The extent to which rats commensal with man display avoidance behavior is perhaps a consequence of selection over the seven thousand years during which civilizations, with its stores of food has existed. More intense selection against wildness and neophobia produced the laboratory rat in less than half a century.

Avoidance of strange objects, and especially, strange animal of the same and other species, is common in the animal kingdom. It develops early in the life of many species of birds and mammals after a brief period when the young become imprinted on their parents. Once this young-parent attachment has been acquired, the safety of the young is well served by their avoidance of other animals. The avoidance behavior of wild rat may have a source in this kind of behavior, but on such question one can only guess.

Whatever its evolutionary origin, the neophobia of wild rat is not by itself sufficient protection against poisoned food. It is combined with a capacity to learn to refuse toxic mixtures. This capacity parallel the ability, much studied in tame rats, to select, in some instances, the nutritionally superior of the food.

The combinations of exploring and avoidance with habit formation is therefore elegantly adapted to giving a rat a maximum of information about the resources and dangers of its environment, in the safest possible way.

ANALYSIS OF ACTIVITY OF RAT

The Cause of Activity

Methods.

Rats habit about when they are getting food or water nest material; when they are finding a mate or site for nesting; and when they are fleeing from predator. But their movements are often by no means obviously related to such activities. To what extent are rats’ movements determined by immediate need?

Laboratory rats have long been described as highly exploratory and inquisitive. One of the earliest studies, that of Small, published in 1899, describes this behavior at length and refers to the restlessness of infant rats as ‘premonitions of curiosity’.

Wild rats, too, are actively exploratory, though this is often obscured by a form of ‘wariness’ which laboratory rats hardly display. Generalized movement about a substantial area can, however, easily be observed in wild rats given access to a strange place; this can be arranged by removing a barrier which has hitherto prevented entry by rats living on adjacent ground, or by putting rats in large and unfamiliar cage.

Sometimes it is possible to account for the movements of an animal in common sense term. In natural condition, and in captivity also, activity may seem obviously to spring from some internal deficit; after an interval without food or water, an animal which has been sleeping or resting goes to a place where it can eat or drink. But not all the ranging movements of rats can be explained in this way.

Consider, for instance, rats which have been deprived of food for twenty-four hours. While they have eaten a good deal and have drunk some water, they carry out a general exploration of the cage. Evidently, in this situation, exploration comes after deficit has been made up.

RAT; STUDIES OF RESPOSIVENESS

The isocortex usually of as a vast organ of learning, but in fact it also influences both the variability of behavior and the intensity with which fixed patterns of behavior are performed .

Krechevsky studied the effects of isocortical damage on exploration by rats. Rats tend to vary their route to a goal when there are alternative paths of similar length. This variations was reduced by the lesions; the reduction was proportional to the extend and independent of locus, of the injury , in the experiments rats with damage brains chose stereotyped path to a goal, whereas intact rats preferred a route which was varied by the experimenter. In these experiments a damage cortex led, then, to preservations of a habit, and therefore to a loss of behavioral adaptability.

Beach has made analogous observations on reproductive behavior. The maternal activities of rats after cortical lesions were impaired in proportion to the size f the injury. There were also a positive correlation between the amount of cortical tissue remaining and the proportion of males still able to copulate. A curious feature was that the deficits could be made up by injecting the appropriate hormone.

Much of the work cited in this and the preceding section suggest that trial-and-error behavior, exploration and also fixed action pattern depend in certain respect on a general action of the whole of isocortex, at least in so lowly a mammal as the rat. The contradiction of the fact of the localization may be only apparent; region of cortex which have specialized functions may have a mass function as well; perhaps there is, as Leshley suggested, a general facilitatory influence of all regions.

In more complex brains, especially those primates, the cortex evidently becomes more differentiated; but even in them there may be some mass action, perhaps especially during early life.

Rat Habit

Habit Formation and Localization

An outstanding example of an attempt to relate brain function to rats behavior was that of K. S Lashley (1890-1958). The animal he principally used were laboratory rats, but he also work on monkey. The behavior studied was the learning of discriminations and simple manipulation , and how to find the way through a maze of branching passages. His method was usually to destroy portion of isocortex, or to make cuts in it, with an electro cattery, and study the effect on behavior.

Lashley himself publish a late review of his work in 1950, other valuable discussion are those Osgood and Zangwill, but Lashley’s own earlier work should be consulted for its historical importance and the elegance and interest of the writing.

Lashley’s most remarkable experiments are those which suggest, that learning any task, regardless of its nature and the senses involved, is a function of the hole cortex; that the ability both to develop new habits and to retain old skills is proportional to the amount, regardless of region, of cortical tissue present (mass action); and that one part of the cortex can take over the functions of other that have been destroy (equipotentiality).

One of the concepts strongly critical by lashley was that of the reflex arc, with of overtones of telephone system, as applied to the brain. He made incisions between the visual and motors area of the cortex of adult rats. He then trained them to make a difficult discrimination; this involved their avoiding cross (X) and approaching triangle when these were presented on a black background, but approaching cross (X) and avoiding triangle on a stripe background . This same to dispose of any simple sensory –motor connections as the basis of learning; but since this worked was done, the extend of connections of the cortex with the thalamus and reticular formation have come to be more fully understood ; and these connections were lefts intact in the experiments.

Rat Brain and Structure

Of all physiological facts, those concerning the brain seem most likely to help to explain behavior; and, although this statement is a truism, we may now ask why it is so. The answer given in this chapter inevitably refers to kinds of behavior and experimental methods, that are more fully described later. The central nervous system is the rat organ through which the sense organs act on the effectors; although all other organs may influence behavior, the CNS and the nerves carry especially large amounts of information to the rat muscles and rat glands. While the blood enables the muscles to remain operational, by carrying substances to and from them, the nervous system determines the moment, durations to the contractions of other muscles.

Neutral action, then, imposed a pattern of activity on dozen of muscles and many millions of muscle fibers. Patterning exists even in a simple reflex. C. S. Sherrington (1859-1952) wrote: "A great principle in the plan of the nervous system is that an effector shall be at the behest of many receptors, and that one receptor shall be able to employ many effectors". This arrangement makes possible the interaction of many afferent inputs to produce the animals pattern of activity.

The brain stem of rat (medulla, pons and midbrain) is, like the spinal cord, largely an assembly of reflex centers; it receives the inputs of the cranial nerves, except the olfactory and most of the optic, and contains the origins of the motor fibers in them. Particular regions are associated with specific reflex acts such as lachrymation, with more complex patterns such as breathing and (in the midbrain) with postural adjustments. There is also a large cerebellum of which the function is evidently the control of the details of movement; it is the cerebellum which (as far as we know) makes the proprioceptive feedback effective. In all this the mammalian brain resembles that of other classes of vertebrates.

Rat Behavior

Rat behavior is meant here the hole of the activities of animal effectors organs, its muscles and glands. The definition includes the contraction of smooth muscle and the secretions of all glands, but most of this book is concerned with behavior in a narrower sense, namely, the movements of the whole animal which depend on the activity of many skeletal muscles.

The account of behavior in this book is wholly in terms of overt activities which can be directly observed, and of physiology which can be studied by well-established laboratory methods. No reference is made to the feelings of rats, their thoughts, their minds, or any of a number of such concepts colloquially used in speaking of human behavior. This restriction is usual (though not universal) in scientific communication, and we may now inquire whether it is necessary. Most people seeing a rat sniffing around near food find it both convenient and sensible to say that the rat is hungry and looking for food; and, is the animal is then disturbed and runs away, to say that it has been frightened.

Most of mammals, rats are greatly influenced by odors. A male can distinguished the odor of a female in estrus from that of a non-receptive female. An unwary human observer, incapable of this olfactory achievement, might attribute the movement of a male toward a female out of sight or hearing to some mysterious and identifiable agency, perhaps called an ‘instinct’, beyond ordinary understanding. Rats also make and hear sounds of too high pitch for our ears. These are example of the different species; the ‘world’ of sense impressions of an animal much influenced by smell, and responsive to sounds of high pitch, is quite different from that of one relying primarily on vision.

Another example is the attribution of a high degree of intelligence of rats. Wild rats are difficult to kill because they avoid traps and poison baits. They consequently often appear intelligent, and one biologist has been led to call the conflict between rats and men ‘a veritable battle of wits’; but careful observation of rats in simple experiment situations has shown that the avoidance of strange things is quite indiscriminate.