I26o 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



areas may also give rise to facilitatory influences. 

 These have appeared in three basic forms: a) aug- 

 mentation of extensor tonus in the ipsilateral fore- 

 hmb, /)) augmentation of extensor tonus in the con- 

 tralateral forelimb, and c) augmentation of ipsilateral 

 extensor tonus as a postinhibitory rebound phe- 

 nomenon. 



Augmentation of ipsilateral extensor tonus and of 

 extensor reflex contractions was noted from time to 

 time as an unexplained deviation from the usual ex- 

 perimental findings (32, 96, 220). The suggestion 

 (96) that the anterior lobe contains a mixture of cells 

 of opposite potentialities received strong support from 

 observations by Moruzzi (232-238) that extensor 

 inhibition was converted into extensor facilitation 

 by the simple maneuver of lowering the frequency of 

 stimulation. This observation has been confirmed 

 (47> 33 1 "334) ^nd indicates that the anterior lobe 

 vermis has the double potentiality for inhibition and 

 facilitation over frequency selective efferent paths. 

 The preponderance of inhibitory observations is 

 probably due to the prevalence of the use of stimuli 

 in excess of 30 to 40 per sec. which activate the power- 

 ful and overwhelming inhibitory mechanisms. 



The auginentation of contralateral extensor tonus 

 in the decerebrate animal which has been empha- 

 sized so strongly by Sprague & Chambers (317) 

 as a predictable result of stimulation of the anterior 

 lobe vermis may now be regarded as an established 

 and regular event accompanying stimulation with 

 slightly higher voltages than required for ipsilateral 

 inhibition. These observations have been confirmed 

 (267, 268) with the added information that contra- 

 lateral augmentation of extensor tonus is supplanted 

 by contralateral inhibition such as originally seen by 

 Sherrington (295) and by Lowenthal & Horsley 

 (187) if the voltage of stimulation is increased slightly 

 more. If activation of the contralateral side of the 

 cerebellum, or of its efferent pathways, is surgically 

 prevented, the contralateral inhibition of tonus with 

 higher voltages disappears and the augmentation 

 reappears. 



The remarkable and dramatic augmentation of 

 ipsilateral extensor tonus following inhibitory stimu- 

 lation, post-inhibitory rebound (32), is the third form 

 of facilitatory reaction which may be evoked by cere- 

 bellar stimulation. Despite its clear and regular 

 manifestations, it still remains unanalyzed. It is pos- 

 sible that rebound contractions are not, strictly 

 speaking, to be ascribed to cerebellar discharge con- 

 tinuing after the cessation of the stimulation. 



Anterior Lobe: Intermediate Portion. The first reliable 



evidence that the anterior lobe is not equipotential 

 over its entire surface was derived from the studies of 

 Stella (318) who noted facilitation of ipsilateral 

 forelimb tonus which was not abolished by removal 

 of the N'ermal portion of the anterior lobe. These 

 results were soon confirmed and extended bv Hamp- 

 son et al. (150-152). In quadrupeds only the medial 

 three fifths or vermal portion of the anterior lobe gave 

 rise to the type of responses just described in the pre- 

 ceding paragraphs. The stimulation of the lateral two 

 fifths, or intermediate portion, on the other hand, 

 produced ipsilateral extensor facilitation coupled 

 with flexor rebound. These observations were con- 

 firmed in the quadruped (230) and in the monkey 

 (151). The monkey shows a broader extension of the 

 facilitatory response, a species difTerence which was 

 also noted by Snider et al. (310). Sprague & Cham- 

 bers (317) also point out that increasing the strength 

 of stimulation augmented the intensity of the response 

 but did not alter its quality. Working with decere- 

 brate preparations which had been subjected to 

 chronic destruction of the fastigial nuclei to eliminate 

 all responses from the vermis, and by careful atten- 

 tion to the state of the preparation and to selection 

 of stimulus parameters, Pompeiano (269, 270) has 

 been able to evoke two types of responses regularly 

 from the intermediate portion of the anterior loije. 

 He divides it into a medially placed strip from which 

 may be elicited ipsilateral active flexion and con- 

 tralateral extension (23, 96, 150, 152) and a laterally 

 placed strip the stimulation of which brings about 

 ipsilateral extensor facilitation (150, 230, 317, 318). 

 It was presumalily during activation of the lateral 

 strip that Granit & Kaada (137) made the very 

 significant observation of augmented gamma neuron 

 discharge (see also 134). 



Anterior Lobe: Efferent Patlts. The distribution of the 

 efferent pathways mediating these various responses 

 has been clarified h\ physiological experiments guided 

 by the detailed anatomical studies of the Oslo school 

 (169). 



Sprague & Chambers (317) have reported thai 

 responses characteristic of the vermal portion of the 

 anterior lobe are duplicated by stimulation of the 

 nuclei fastigius, the inferior cerebellar peduncle and 

 the medial reticular formation of the medulla, ob- 

 ■servations which have been confirmed by Ricci & 

 Zanchetti (279). These results thus support the ob- 

 servations of Bernis & Spiegel (23) that inhibition 

 from the anterior lobe vermis is abolished by section 

 of the inferior cerebellar peduncle. 



In a careful series of experiments, Moruzzi & 



