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HANDBOOK OF PHYSIOLOGY 



NEUR(3PHYSIOLOGY II 



reflexly-evoked phasic contractions and voluntarily- 

 controlled phasic contractions is an important one 

 which should be borne in mind. 



Through the many years of endeavor on the part 

 of physiologists and clinicians to describe the dis- 

 orders of posture and movement following cerebellar 

 lesions, a complicated terminology developed in which 

 similar words were often used with different meanings. 

 We owe to Holmes (158) the present system of defini- 

 tions which he evolved in his classic papers on cere- 

 bellar disease in man. This nomenclature was soon 

 adopted by clinicians. Walker & Botterell (354) intro- 

 duced these definitions into the physiological liter- 

 ature and they have been generally used by physi- 

 ologists since that time. The most important of these 

 terms are: a) cerebellar ataxia, a general term em- 

 bracing all motor phenomena of cerebellar deficiency 

 including dysmetria, tremor, decomposition of move- 

 ments, etc.; h) dysinetria, any disturbance in the 

 range of voluntary movement; r) hypermetria, an 

 excessive range of movement or overshooting; d) 

 hypometria, deficient range of movement resulting 

 in a failure to reach a goal ; e) decomposition of move- 

 ment, deficiency in the proper sequence and timing 

 of the components of a motor act;/) tremor, trembling 

 or oscillatory movements at rest (static tremor), dur- 

 ing an active movement (kinetic tremor) or the coarse 

 'hunting' oscillations occurring at the time of ap- 

 proach to a goal (terminal tremor); g) tonus, the 

 slight constant tension of healthy muscles which 

 contriljutes a slight resistance to passive displacement 

 of a limb; and /;) hypotonia, deficiency in tonus mani- 

 fest as a diminished resistance to passive movement. 



All submammalian forms have been subjected to 

 a certain amount of experimentation with varying 

 degrees of control and with varying degrees of pro- 

 ductiveness. The older literature on these forms has 

 been reviewed by ten Gate (325 to 327). Bremer and 

 his colleagues (34, 45) and Chiarugi & Pompeiano 

 (69) have more recently done carefully controlled 

 studies on the ablation of the cerebellar cortex and 

 nuclei in birds. Space limitations permit only the 

 observation that these studies demonstrate that, in 

 some respects, birds react difTerently to cerebellar 

 ablation than mammals and that special problems are 

 thus encountered. Nevertheless, the decerebellate 

 bird has been reported to show an exaggerated posi- 

 tive supporting reaction (45) comparable to that later 

 described in the mammal (277). 



Total Ablation 



The many experiments performed by Luciani, ex- 

 tending over a span of 10 years, first described in 

 Italian in 1891 (188), later in German (189) and then 

 in English (190), still stand as a solid foundation 

 underlying the results of later studies on the effects 

 of cerebellar ablation. Although his descriptions have 

 not gone without challenge from time to time, there 

 is at present almost no need for change or emenda- 

 tion. Luciani divided the postoperative course of his 

 animals into three phases. His first stage constituted 

 a period of excessive motor activity, a period of dy- 

 namic signs which he referred to as 'functional ex- 

 haltation.' The second stage was a period during 

 which motor deficiencies were the outstanding charac- 

 teristic of the animal's behavior. The third stage 

 constituted a stable state which developed as the 

 animal became able to compensate for his deficiencies. 

 Luciani gave reason to consider that compensation 

 occurred in two ways: a) through a process of organic 

 compensation involving new activities on the part 

 of remaining portions of the brain and h) through a 

 process of functional compensation by virtue of which 

 the animal learned to correct the deficits produced by 

 cerebellar ablation. As Moruzzi & Dow (241) point 

 out, the processes of compensation undoubtedly start 

 immediately after the production of a cerebellar lesion. 

 For this reason they consider it more logical to sub- 

 divide the postoperative course into a period of un- 

 stabilized deficiencies and a period of stabilized de- 

 ficiencies. In the paragraphs to follow, an attempt will 

 he made to describe the various manifestations of 

 cerebellar remo\'al in terms of their functional nature, 

 considering first the subprimate forms and indicating 

 the important difTerences which have been noted in 

 the primates. 



SIGNS OF INHIBITORY wiTHDRAW.^iL. During the first 

 5 to 10 days following total remo\al of the cerebellum, 

 dogs and cats are agitated and restless. They are 

 unable to stand, and, lying in the cage, exhibit periods 

 of exaggerated opisthotonus coupled with rigid ex- 

 tension of the forelimbs, alternating clonic move- 

 ments of the hind limbs and ocular convergence (113, 

 114, 182, 183, 188-190, 274-277, 335). As improve- 

 ment occurs and the animal attempts to attain the 

 upright posture, the forceful extension of the fore- 

 limbs often throws the animal over onto its back. 



Luciani was unable to establish firmly the reason 

 for this behavior, considering it most probably to be 

 due to irritation and iniurv discharges from the site 



