Abstract
The beginning and development of the spontaneous electric activity obtaining from the exposed cortex were examined in various young animals in the pre-and postnatal growth. The animals used were albino rats, guinea pigs, chicks, and pigeons. Guinea pigs and chicks present the spontaneous electric activity in an early embryonic stage as observed by the previous writers, while albino rats and pigeons do show this activity only in the postnatal life. In albino rats it is possible to initiate the spontaneous electric activity after the rats are 5 days old and in pigeons after the age of about 4 days.
The onset of the spontaneous electric activity seems to reflect ecologically the difference found between the animal classes which can stand and feed by themselves as soon as birth, and those which do not leave the nest for a while after birth. In all these animals the cortical electric response by afferent stimulation is elicitable for a certain period after the spontaneous electric activity appeared.
Cytological examination of the cortical cells in albino rats and pigeons reveals that the spontaneous electric activity will be initiated before nerve connection between the cortical and the subcortical regions is established. The appearance of the spontaneous electric activity seems to be timely correspondent with that of Nissl substance in the nerve cells.
