CHARLES H. SAWYER 165 



violent rolling, neck-rubbing, etc. (43), which continues intermittently for 

 several minutes. 



Use has been made of the estrous or primed cat to study, with Dr. Porter 

 and i\Ir. Cavanaugh (25), the effects of vaginal stimulation on the electrical 

 activity of the hypothalamus. Six electrodes were stereotaxically placed within 

 the hypothalamus and multiple recording was carried out under cyclopropane, 

 chloralosane or curare. Two consistent patterns of altered electrical activity 

 were revealed in the lateral hypothalamic area in and around the medial fore- 

 brain bundle. The tirst was characterized by an increased frequency up to 18 

 cycles per second, and heightened amplitude of the waves, beginning during 

 stimulation, persisting some 15-45 seconds and returning as spindle-like bursts 

 during the next 2-5 minutes. In unanesthetized cats under curare an additional 

 type of activity was noted: recurrent bursts of synchronous activity with a two- 

 fold increase in amplitude and a slow frequency of 4-6 cycles per second, con- 

 tinuing up to about 5 minutes after cessation of stimulation (fig. i). Although 

 curare prevented movement during the recording, the bursts appear to be tem- 

 porally related to the active periods of the after-reaction in the unrestrained 

 non-curarized cat. While present in 10 of 13 estrous or primed cats, the altered 

 electrical patterns were absent in 9 anestrous animals which failed to give evi- 

 dence of either behavioral after-reactions or pituitary stimulation following 

 vaginal stimulation. 



Also employing the stereotaxic technic in cats with ]\Ir. Robison (27), we 

 have been stimulating electrically various regions of the hypothalamus and, 

 at the end of stimulation, making electrolytic lesions with the stimulating 

 electrodes. The areas responding positively to electrical stimulation under 

 chloralose anesthesia by inducing ovulation also react to lesions by blocking 

 subsequent copulation-induced ovulation. These regions are considerably more 

 extensive than the area from which the changes in electrical activity were re- 

 corded. They appear to extend from the ventromedial nuclear region back to 

 the mammillary bodies, but not forward into the anterior hypothalamus. Be- 

 cause some of the cats in this investigation are still living, precise localization 

 must await autopsy and a histological study of the brains. 



In the rabbit brain, widespread areas of the hypothalamus from the preoptic 

 region to the mammillary bodies have responded to direct electrical stimulation 

 by activating release of ovulating hormone (15, 17, 20, 23). Negative results 

 have been reported from stimulating too near the midline or too far laterally; 

 these parasympathetic zones actually inhibit ovulation (20). Koikegami et al. 

 (19) recently reported ovulation in rabbits following strong electrical stimula- 

 tion of the amygdaloid nuclei. With Dr. Tokizane (40), we have more recently 

 stimulated various amygdaloid nuclei, while simultaneously recording electri- 

 cal activity in various cortical and subcortical regions approached stereo- 

 taxically (34). It appears that stimulating lateral amygdaloid nuclei at a voltage 



