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.