THE CEREBELLUM 



'-^49 



The medial nuclei receive cortical projections from 

 the vermian portions of both anterior and posterior 

 lobes. Cortical projections from the intermediate 

 portion of the anterior lobe and hemisphere, from 

 the paramedian lobule, and to a certain extent from 

 the paraflocculus terminate in the intermediate 

 nuclear group. The lateral nuclear group receives its 

 corticonuclear fibers from the lateral portions of the 

 hemisphere and from the paraffocculus. This cortico- 

 nuclear projection is strictly ipsilateral. The anterior 

 portions of the cerebellum project into the anterior 

 portions of each of the nuclear groups, and posterior 

 onto the posterior, in a perfectly regular pattern. 

 This systematic relationship between the cortex and 

 the nuclei is the anatomical basis for the sagittal sub- 

 divisions of the cerebellum mentioned earlier. 



The outflow from the various cerebellar nuclei has 

 been a difficult and confusing problem for many 

 years. Perhaps the most clear-cut description of the 

 relationships is afforded by Jansen & Brodal (169). 

 Since a thorough appreciation of these outflow path- 

 ways is essential to an interpretation of many phys- 

 iological investigations, no attempt will be made to 

 outline the facts here. Rather the reader is referred 

 to the more complete discussion. 



In considering cerebellar influences upon other 

 portions of the brain, it is essential to bear in mind 

 that some Purkinje cell axons from all parts of the 

 vermis and from the flocculus leave the ccreijcUum 

 without interruption (167, 168). These axons termi- 

 nate primarily in the vestibular nuclei ipsilaterally to 

 their origin. 



Extracerrhellar Rtlalions 



The cereijellum is related to the remainder of the 

 nervous .system by fibers coursing througli the three 

 cerebellar peduncles. The principal inflow to the 

 cerebellum from the medulla and the spinal cord 

 occurs through the inferior cerebellar pechmcle. 

 Through this structure come impulses from spinal 

 cord nuclei, from the inferior olivary nucleus, from 

 the dorsal column nuclei, from the vestibular nuclei 

 and from the reticular nuclei of the medulla. Out- 

 flow paths through the inferior peduncle relate the 

 cerebellar cortex and nuclei to the vestibular nuclei, 

 the inferior olivary nuclei and the reticular nuclei. 

 The middle cerebellar peduncle is composed almost 

 entirely of fibers originating in the nuclei of the pons. 

 Through this pathway the cerebellar cortex, prin- 

 cipally of the hemispheres, the vermis and the para- 

 flocculus, is subjected to the influence of most por- 



tions of the neocortex of the cerebral hemispheres. 

 The superior cerebellar peduncle contains fibers of 

 the ventral spinocerebellar tract and some fibers 

 from the tectum and tegmentum. Its great bulk, 

 however, is made up of axons from all of the cere- 

 bellar nuclei destined for the thalamus, the red 

 nucleus, the motor nuclei of the brain stem, and the 

 reticular nuclei of the mesencephalic, pontine and 

 medullarv tegmentum. 



CH.'^R.'\CTERISTICS OF CEREBELL.OiR ACTIVITY 



The characteristics of activity of cerebellar 

 neurons, like those of other portions of the central 

 nervous system, have been studied rather intensively 

 only during the last 1 5 years. Very early attempts to 

 apply electrophysiological techniques to this proi)lem 

 were made by Beck & Bikeles (ig, 20) and Camis 

 (57) utilizing inadequate recording techniques. More 

 recently, advances in electrophysiological techniques 

 have made possible the acquisition of information 

 important from both the physiological and the ana- 

 tomical points of view. 



Spontaneous Cerebellar Activity 



ELECTRlC.'SiL ACTIVITY OF CEREBELLAR SURFACE. Thc 



first recognition of the characteristic electrical ac- 

 ti\ity of the cerebellar cortex was made by Adrian 

 in 1935 (i). Since that time it has been found that 

 the cerebellar cortices of the fish (342), the amphib- 

 ian (21), the reptile (91) and the bird (54, 55, 360) 

 display a pattern of activity essentially similar to 

 that seen in mammals, a datum which permits the 

 inference that this basic activity is dependent upon 

 some intracortical organization of neurons which is 

 peculiar to this anatomically uniform cortex. The 

 typical electrocorticogram from the surface of the 

 cerebelhmi consists of roughly rhythmic potential 

 oscillations of frequencies in the range of 150 to 250 

 per sec. The voltages recorded may vary from .020 

 to .120 mv, depending apparently upon the general 

 condition of the preparation (240). Dow (106) soon 

 confirmed Adrian's observations and added further 

 information of importance. This rhythmic surface 

 activity was shown to originate within the cerebellar 

 cortex, to be correlated with evidences of cerebellar 

 influences on extracerebellar structures, and to be 

 exceptionally vulnerable to hypotension and easily 

 depressed by anesthetics, anoxia and ischemia. The 

 existence of the fast cerebellar rhythm has been 



