INTERPEDUNCULAR NUCLEUS >0J) 



in destroying by electrocautery the periaqueductal gray of cats with- 

 out injury to surrounding parts. This lesion must have involved the 

 dorsal longitudinal fasciculus and the dorsal tegmental nucleus. If 

 the injury is slight, the cats on awakening from the anesthetic are 

 very wild and active but after a few days recover normal behavior. 

 This seems to be an irritative excitation. If the lesion is extensive, 

 the cats "lie inert, silent and flaccid as a wet rag." They never again 

 show any spontaneous activity, though after a few days placing reac- 

 tions are elicited normally and, if stimulated, they may walk slowly. 



If now it is assumed that the dorsal longitudinal fasciculus con- 

 tains fibers which normally transmit some sort of continuous non- 

 specific activating or facilitating influence upon the entire motor 

 field of the lower brain stem — an influence which is essential for ef- 

 fective co-ordination and integration of these local systems of syner- 

 gic muscular activity — then the destruction of this pathway would 

 leave the animal helpless. This is not a flaccid paralysis, because the 

 animal ultimately regains control of righting and placing reactions 

 and even co-ordinated locomotor movements. All initiative and 

 spontaneous activity are permanently lost because the animal is de- 

 prived of some essential component of the integrating apparatus. 

 The "obstinate progression" that follows destruction of the inter- 

 peduncular nucleus may result from loss of an essential inhibitory 

 influence normally acting upon the dorsal tegmental nucleus and the 

 f. longitudinalis dorsalis. Loss of this influence allows the remaining 

 apparatus of facilitation in the f. longitudinalis dorsalis to "race" 

 like a steam engine deprived of its governor, and in this particular 

 setup of conditions the result is uncontrolled progression. 



In Rabat's ('36) study of alterations in respiration resulting from 

 electrical stimulation of cats, it was reported that stimulation of the 

 periaqueductal gray and of diencephalic regions known to contrib- 

 ute fibers to the dorsal longitudinal fasciculus was followed by in- 

 crease in rate and amplitude of respiration. Shallower and unusually 

 slower breathing followed stimulation of the habenula and habenulo- 

 interpeduncular tract. 



Detwiler has shown (p. 6'2) that in Amblystoma a nonspecific 

 mesencephalic influence is essential for the maintenance of motor 

 efficiency. This is in addition to the action of the apparatus which 

 activates patterned behavior, the latter maturing earlier and quite 

 independently of cerebral influence. This mesencephalic influence in 



