THE CEREBELLUM 



1253 



paramedianus (H VII B, H \'III A). Similar re- 

 sults were obtained in the lightly pentobarbitalized 

 rat (iio). This generalized distribution of response 

 was not reported by later insestigators working 

 largely with animals under the influence of barbi- 

 turate anesthesia. These differences have been made 

 the subject of a special study by Combs (75). Utiliz- 

 ing both natural and artificial stimuli, Combs found 

 that responses were diffusely distributed over the 

 anterior lobe (I-V, H I-H V) and simplex (\'I and 

 H \'I) in the decerebrate unanesthetized animal. 

 The diffuse responses were not the result of intra- 

 cortical spread because they appeared with relatively 

 uniform latency over the entire lobe and furthermore 

 survived rather deep and extensive ablations of those 

 portions of the cortex from which others had re- 

 corded localized responses. Following the adminis- 

 tration of pentobarbital to the same animals, the 

 responsive zone shrank to a small ipsilateral region of 

 the intermediate portion of the anterior lobe, the 

 exact location of which was characteristic of the site 

 of stimulation. These obser\ations were tentatively 

 explained by postulating the existence of two afTerent 

 systems differentially susceptible to pentobarbital, 

 an hypothesis which has been supported by addi- 

 tional observations (76). The localized response in 

 the anesthetized animal was shown to be independent 

 of the dorsal and ventral spinocerebellar tracts, the 

 spino-olivocerebellar system and the external cuneate 

 nuclei, but disappeared upon destruction of the 

 lateral reticular nucleus. It would thus appear that 

 impulses of somesthetic origin are delivered diffusely 

 to most of the anterior lobe and simplex and to the 

 paramedian lobes by one or more ascending systems, 

 whereas other ascending systems deliver only to 

 restricted foci within this larger responsive area. It 

 would appear possible that examples of interaction 

 of evoked responses at one point on the cerebellum 

 froin widely separate afferent sources (28, 41, 216, 

 217) may have been dependent upon the utilization 

 of experimental preparations showing the generalized 

 responses described by Combs (75). 



The localized responses from hind limb regions, 

 when studied in anesthetized animals, appear ipsi- 

 laterally in the culmen (IV, V, H IV, H V), from 

 fore limb regions in the culmen (IV, V, H IV, H V) 

 and from face areas in the simplex (VI, H \T) (2, 

 312). In addition to these responses from the anterior 

 lobe, localized responses may also be recorded from 

 the paramedian lobes (H \II B, H VIII A) bi- 

 laterally with considerable overlapping of foreleg, 

 hind leg and face areas (312). Occasionally, responses 



from somatic stimulation are recorded from the 

 ansiform lobules (H \'II A) (312). The distribution 

 of activity from deep and superficial sources shows 

 no detectable differences (216, 217). 



From vestibular sources also, evoked potentials 

 appear in these portions of the cerebellum known 

 anatomically to be closely related to vestibular func- 

 tion. Thus, single shocks applied to vestibular struc- 

 tures produce evoked potentials in the flocculonodu- 

 lar loije, the uvula (IX), lingula (I) and lobulus 

 centralis (III) as well as in the fastigial nuclei (107). 



Natural stimulation of auditory receptors, as well 

 as natural and artificial stimulation of visual input, 

 has produced responses in the simplex (VI, H \T) 

 and in the folium and tuber vermis (VII A, VII B) 

 (312). Visual responses have also been recorded from 

 the ansiform lobule (H VII A) and are more easily 

 found when the animal is anesthetized with chloralose 

 (312). This characteristic has resulted in the sug- 

 gestion that the ansiform lobule responses are ab- 

 normal in the sense that they depend upon the con- 

 vulsant properties of chloralose (128, 129). Evidence 

 as to the ph\ siological nature of these responses and 

 their independence of chloralose has recently been 

 presented (117). 



As a result of stimulation of vagus nerve fibers (95) 

 and olfactory bulbs (162), responses have been re- 

 corded from the same zones which are activated by 

 tactile impulses from the face. Single shock stimula- 

 tion of the splanchnic nerve with currents strong 

 enough to activate thin myelinated fibers of the delta 

 category produces evoked responses in various por- 

 tions of the vermis (I\', \', \"I, VII A, \'II B) and 

 from the paramedian loijules (H \'II B, H \'III A) 

 (362). 



IMPULSES FROM CEREBRAL CORTEX. AUusion has al- 

 ready been made to the fact that spontaneous cere- 

 bral rhythms may ha\e an influence upon the ac- 

 tivity of the cerebellar cortex. As might be expected, 

 acti\ity initiated by artificial stimulation of the 

 cerebral cortex may al.so evoke responses from the 

 cerebellum. Such responses have been valuable in 

 establishing the existence of functional pathways 

 between these two portions of the central nervous 

 system in support of and in extension of the more 

 purely anatomical descriptions. 



Starting from the observations of Curtis in 1940 

 (93), subsequent investigations have supplied con- 

 firmation and refinement. In the anesthetized cat, 

 electrical (93, 108) and chemical stimulation of 

 manv areas of the cerebral cortex elicits rather 



