1256 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



which are thousjht to lie produced Ij\ the afferent 

 volleys. It would thus appear that systcmically ad- 

 ministered strychnine not only produces convulsive 

 outbursts in motor elements of the brain stem and 

 spinal cord but also initiates similar patterns of ac- 

 tivity in ascending systems which reflexly induce the 

 cerebellar rhythin. 



Con\ulsi\e acti\it\' of the cerebellar cortex is also 

 said to follow the administration of DDT (92) and 

 ^-chlorinated amines (261). 



silence enduring; for some 50 msec. In a more com- 

 pleteh- reported study, Goldman & Snider (132) de- 

 scribe somewhat different patterns of activity from 

 the brachium conjunctivum of curarized cats in re- 

 sponse to stimulation of the inferior olive, the resti- 

 form bodies and the brachium pontis. These authors 

 ascribe a i.o to 1.5 msec, component of the evoked 

 response to a monosynaptic activation of the cere- 

 bellar nuclei and a 2.5 to 3.0 msec, component to a 

 corticonuclear relav. 



Cerehfllofiignl Arlivity 



CEREBELL.\R .NUCLEI. Electrophysiological studies of 

 the activity of the cerebellar nuclei ha\e been car- 

 ried out only recently. Arduini & Pompeiano (8, 

 271 ) have studied acti\ity in single units of the rostral 

 pole of the fastigial nuclei during various forms of 

 induced activation. As would ha\e been predicted, 

 many of these units were tonically active. This tonic 

 activity could be altered by surface polarization of the 

 cerebellum (49, 50), by galvanic stimulation of the 

 labyrinths and by stimulation of somatic .sensory 

 pathways. Cerebellar influences were most readily 

 obtained from the vermal portion of the culmen 

 (IV-V) and movement of the surface electrode i to 

 2 mm onto the intermediate portion (H IV, H V) 

 was sufficient to abolish the response (see 168). Ac- 

 tivity of units in the rostrolateral part of the nucleus 

 was usually augmented, whereas activity of units in 

 the rostromedial part of the nucleus was usually in- 

 hibited. Units which were not affected by cerebellar 

 stimulation may have been related to inaccessible 

 portions of the cortex, association neurons, or in- 

 dependently active fastigial elements (316). 



CEREBELLAR PEDUNCLES. Electrophysiological studies 

 of the activity patterns in the cerebellar peduncles 

 are also rather rare. Spike discharges in the superior 

 cerebellar peduncle of the a;oat have been recorded 

 (83, 84) in response to stretch of extrinsic ocular 

 muscles and various forms of sensory stimulation. 

 Latencies of discharge and the finding of similar pat- 

 terns in other portions of the cerebellum and cortex 

 led to the conclusion that the actixatcd fibers were 

 cerebellofugal in type. Microelectrode recordings 

 from the superior cerebellar peduncles in the de- 

 cerebrate cat have revealed that a complex potential 

 of four components may be evoked by sensory stimu- 

 lation (56). Reasons are given for identifying the 25 

 to 30 msec, component as the efferent discharge. The 

 evoked potential is followed by a period of electrical 



ACTIVITY SECONDARILY INDUCED BN' CEREBELLOFUGAL 



IMPULSES. Alterations in the actisity of other portions 

 of the brain induced by control of cerebellofugal ac- 

 tivity has been studied using two different techniques. 

 The time-honored system involving the production of 

 synchronized volleys with single shocks and recording 

 with microelectrodes has been used to good ad- 

 vantage by some (156, 310, 359J. Moruzzi and his 

 colleagues have capitalized on the responsiveness of 

 cerebellar neurons to polarization (49, 50) and have 

 recorded the resultant secondary changes with 

 microwire electrodes {97, 130, 213, 293, 349, 350, 

 361). These studies have been concerned with 

 secondary activity in the bulbar reticular formation, 

 the vestiljular nuclei, the midbrain and diencephalon, 

 and the cerebral cortex. 



In barbitalized cats. Snider et al. have recorded 

 responses from the bulbar inhibitorv reticular forma- 

 tion evoked by single shock stimulation of the culmen 

 and fastigius (310). The shorter latency of the re- 

 sponses evoked by fastigial stimulation as compared 

 to cortical stimulation was regarded as support for 

 the existence of a corticofastigioreticular pathway for 

 cerebellar inhibition. This suggestion has been 

 strongly supported by the results of microwire reticu- 

 lar unit recording. Using careful anatomical and 

 phvsiological controls, Mollica et al. (213) have been 

 able to identify inhibitory reticulospinal units. The 

 discharge frequency of such units was augmented by 

 polarization of the cortex which produced collapse 

 of decerebrate rigidity. Other units of uncertain 

 identity were inhibited by cerebellar polarization 



(■-^13. -^93. 349. 350)- 



It has been possible to demonstrate convergence of 

 cerebral and sensory as well as cerebellar influences 

 on this latter type of unit (349, 350). Cerebellar in- 

 hibition was effective in decreasing the response to 

 cerebral and sensory volleys and summed with in- 

 hibitory volleys of cerebral origin. Gauthier et al. 

 (130) present evidence that the principal projection 

 to the reticular formation originates from the vermis 



