THE CEREBELLUM 



1263 



of Stimulation of the pyramis in that they induce ipsi- 

 lateral inhibition and contralateral facilitation of 

 rigidity (244, 247). Stimulation of the interpositus is 

 reported to produce an increase in ipsilateral rigidity 

 (272), but the flexor rebound noted by previous in- 

 vestigators (153, 154, 317) was not observed. Koella 

 notes that influences upon decerebrate rigidity origi- 

 nating in the labyrinths summate with the effects of 

 stimulation of various points in the interior of the 

 cerebellum (173). The same author has also described 

 the complicated movement patterns which may be 

 provoked in the unrestrained unanesthetized animal 

 bv stimulation of the medial basal portions of the 

 cerebellum (174). 



Cerebellocerehral Interactions 



It was indicated earlier that influences originating 

 in the cerebellar cortex have been shown to aff^ect the 

 motor functions initiated at the cerebral cortex and the 

 electrical activity of the cerebral cortex. 



MOTOR FUNCTIONS. Cerebellar stimulation has been 

 demonstrated to influence motor functions of the 

 cerebral cortex using both the threshold to stimulation 

 and the responses evoked by stimulation as criteria for 

 study. Rossi's original observation (282) that the 

 threshold of the motor cortex to electrical e.xcitation 

 is lowered during stimulation of the ansiform lobules 

 (H VII A), paramedianus (H VH B, H VIII A) 

 and the posterior vermis (VI to IX) have been ade- 

 quately confirmed (36, 114). No somatotopic ar- 

 rangement was detected in these studies. 



Lowcnthal & Horsley (187) early reported that 

 movement evoked by stimulation of the motor cortex 

 was augmented by stimulation in the area of the 

 lateral vermis near the hemisphere. Using both the 

 convulsive discharge of the motor cortex occurring 

 during chloralose anesthesia as well as strychnine- 

 induced clonus, Moruzzi (227-229) has described 

 both facilitatory and inhibitory results from stimula- 

 tion of the cerebellum. With stimulation of the culmen 

 (IV, V) phasic and clonic movements would ijreak 

 through a background of tonic inhibition. From the 

 ansiform lobule (H VII A) subthreshold convulsive 

 activity could be converted into overt con\ulsions. 

 As was the case for decerebrate rigidity and for re- 

 flexly evoked contractions, cortically-induced phasic 

 movements were also inhibited (309, 310) by stimula- 

 tion of the culmen (IV, V) in the cat and more pre- 

 dominantly augmented by anterior lobe stimulation 

 in the monkey (308). From the intermediate and 



lateral parts of the vermis and from the paramedian 

 lobules, evidence of somatotopic organization was 

 derived (308). 



The question of locus of these effects has not been 

 dealt with critically. Facilitation and increase of ex- 

 citability may be a cortical or a brain-stem function, 

 as may be inhibition (6, 349, 350). 



ELECTRIC-^L ACTIVITY OF CEREBR.'kL CORTEX. TwO 



types of alteration of electrocortical activity have been 

 described as resulting from cerebellar stimulation. 

 Walker observed an increase in the rate and amplitude 

 of cortical waves in the motor areas of the cat 'en- 

 cephale isole' during stimulation of the cerebellar 

 hemispheres (353). Similar effects have been ob- 

 served as a result of application of strychnine to the 

 lobulus ansiformis (H VII A) and appear only in 

 the contralateral sigmoid gyrus (60). Picrotoxin, 

 prostigmine, pentylenetetrazol (Metrazol) and di- 

 isopropylfluorophosphate (DFP) produce similar 

 changes when applied to the ansiform lobule (88). 

 On the other hand, electrical (87, 213, 242) and chem- 

 ical (88) stimulation of the vermis converts the 

 rhythmic activity of the resting cortex into the low 

 voltage fast activity of the arousal and initiates changes 

 in the steady potential of the cortex (103). Even 

 seizure activity is reported to be desynchronized by 

 cerebellar stimulation (305). Cooke & Snider (80) 

 indicate that this sort of change can be produced from 

 many portions of the cerebellum and interpret their 

 results as indicative of a localized cerebellocerebral 

 relationship. 



It appears most probable that the localized effects 

 on the motor cortex are mediated over the dentato- 

 rubrothalamic pathways whereas the production of 

 a generalized activation pattern is a function of cere- 

 belloreticular paths. 



Stimulation Through Chronii ally-Implanted Electrodes 



Recognizing the barriers to the acquisition of com- 

 plete information presented by the necessity for work- 

 ing either in the presence of depressing anesthesia or, 

 alternatively, against the background of disturbed 

 postural tonus of the decerebrate animal, several 

 studies have been carried out using chronically- 

 implanted electrodes to stimulate the cerebellum in 

 freely-moving unanesthetized animals. 



From points scattered over the ansiform lobules 

 (H VII A), the paramedian (H VII B, H VIII A) 

 and the posterior vermis (VI-IX), and from a few 

 points on the posterior edge of the anterior lobe (V), 



