Electrical activity of superior colliculus associated with eye movements in alert cats

Eye movement potentials (EMPs) were recorded from the superior colliculus (SC) of awake cats. When cats moved the eyes in front of a patterned or diffuse field, the EMP appeared as a sequence of the three components; EMP1, EMP2 and EMP3. The EMP1-EMP2-complex occurred while the eyes were moving and it had a wave form similar to that of the flash-evoked response. The EMP3 was seen 30-50 msec after the end of eye movement. In dark only the EMP3 was observed; its delay after the end of eye movement was as large as 70 msec. By placing electrodes at various depths of SC, the EMP was found to originate in the superficial layers. In immobilized, encéphale isolé cats, placed in dark or made blind by enucleation, the followings were observed; 1) Passive movements of the eye did not give rise to any significant electrical activity of SC. 2) Spontaneous mass activity of the oculomotor nucleus, that would result in eye movements if the cats were not paralysed, was followed by sharp wave activity of SC and this was the same after the visual cortex had been ablated bilaterally. From these findings it is concluded for the EMPs of awake cats that the EMP1-EMP2-complex is a response to retinal impulses caused by movements of images, whereas the EMP3 is due to an extraretinal factor such as the corollary mechanism. Besides the EMPs as described above, some activity was found to occur about 150 msec before the onset of eye movement. This EMP, called early EMP, seemed to appear when it was followed by eye movements with relatively high speeds.