1262 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



w hilc not productive of primary alterations of motor 

 neuron activity, has been found capable of allerina; 

 the motor functions of the cerebral cortex. This in- 

 fluence of the cerebellar cortex upon phenomena re- 

 lated to cerebral function has been demonstrated in 

 terms of a) changed cortical excitability to chemical 

 and electrical stimulation, b) alterations produced 

 in movement evoked by stimulation of the cerebral 

 cortex and c) alterations in the electrical activity of 

 the cerebral cortex. In order to avoid presenting the 

 distorted impression that only hemispheral stimula- 

 tion alters cerebral function, it will be more con- 

 venient to consider these studies in a separate section 

 devoted to cerebellocerebral relations. 



Flocculonodular Lobe. The flocculus and nodulus 

 (X, H X) are so near the medulla that effective stimu- 

 lation localized to this portion of the cerebellum prob- 

 ably has never been achieved (251, 287). 



OTHER FORMS OF STiMCL.^TioN : Chemical. Of the older 

 studies of chemical stimulation, perhaps the most 

 demanding of attention were those of Pagano (257, 

 258). Pagano reported experiments performed on 

 unanesthetized dogs wherein he stimulated the cere- 

 bellum h\ injections of curare into the substance of 

 the cerebellar cortex. Injections into the hemisphere 

 were reported to produce ipsilateral tonic movements 

 followed by generalized seizures, the later dependent 

 upon the motor cortex. Similar injections into the 

 vermis were reported to produce behavior patterns 

 like those seen in deep anxiety and extreme fear. 

 Pagano's conclusions concerning the role of the cere- 

 bellum in the sphere ot emotion and emotional ex- 

 pression aroused considerable controversy which has 

 been reviewed bv ten Gate (324) and van Rijnberk 



(348). 



In later years, chemical stimulation, principally 

 with strychnine, has been used largely as a control 

 procedure to verify the cortical origin of responses to 

 electrical stimulation of the cerebellar cortex (207- 

 209, 298). The reported observations fall well into 

 line with observation of responses to electrical ac- 

 tivation. 



Mechanical. Mechanical stimulation presumably 

 produces its results by initiating a discharge of im- 

 pulses from injured and dying cells and thus is not a 

 reversible procedure. It does have the advantage that 

 local injury of the cerebellar cortex will produce re- 

 sponses which can reliably be interpreted as originat- 

 ing from the injured focus, rather than from some 

 nearby structure. Clark's studies (71) with their ex- 

 cellent histological controls are inidoubtedly the most 



reliable of this group. Mechanical stimulation pro- 

 duces the same pronounced responses and prolonged 

 aftereffects as electrical stimulation in the unanesthe- 

 tized animal. The results of electrical stimulation will 

 be described in detail below. 



■Stimulation uj Interior of Cerebellum 



The original studies of Horsley & Clarke, in which 

 the first application of the stereotaxic technique was 

 made (160) were carried out on deeply anesthetized 

 monkeys, and while responses were produced by 

 stimulation of deeper portions of the cerebellum the 

 profundity of anesthesia undoubtedly interfered with 

 the reliable demonstration of function. Poorly con- 

 trolled studies were also made by others {250, 291). 



Miller & Laughton {211, 212) stimulated the sur- 

 gically exposed cerebellar nuclei in decerebrate cats 

 and, in spite of trauma and poor general state of the 

 preparation, were able to obtain reliable responses. 

 Activation of the dentate nucleus was accompanied by 

 ipsilateral foreleg flexion with little contralateral 

 effect. The interpositus and the globosus produced 

 similar forelimb flexion accompanied by contralateral 

 extensor inhibition, the cessation of stimulation being 

 followed by rebound. Activation of the fastigius pro- 

 duced strong active flexion of both forelimbs with 

 powerful rebound. 



The technique of Horsley & Clarke has been re- 

 applied to lightly anesthetized cats (154, 196), de- 

 cerebrate cats {153) and lightly anesthetized monkeys 

 (195). Several varieties of responses were obtained 

 during careful mapping of the interior of the cere- 

 bellum which cannot be completely reviewed here. 

 It is enough to note that dentate stimulation was not 

 characterized by any specific variety of responses. 

 Stimulation of the intermediate nuclei produced local 

 limb responses consisting of relaxation from any exist- 

 ing posture followed by poststimulation rebound to 

 that posture. Fastigial stimulation produced responses 

 in all four limbs, flexion ipsilaterally and extension 

 contralaterally, with strong poststimulation rebound 

 which was not dependent upon afferent activity from 

 limb proprioceptors or vestibular afferents. 



The serial stimulation of portions of the cerebellum 

 in an attempt to define the cerebellofugal pathways 

 has been mentioned in the section devoted to that 

 subject. In addition to such studies, others have been 

 devoted primarily to a definition of the responses to 

 nuclear stimulation in selected portions of the cere- 

 bellar nuclei in decerebrate cats. Stimuli applied to 

 the caudal pole of the fastigius reproduce the results 



