HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



confirmed by numerous investigators (8i, 143, 320, 

 363). Furthermore, the origin of the rhythm has 

 been localized to the Purkinje cell-granular layer and 

 has been differentiated from the single action po- 

 tentials of cerebellar units (52), and the rhythm has 

 been shown to persist in spite of neural isolation of 

 the cerebellar cortex (89 1. In addition to the fast 

 (150 to 250 per sec.) rhythm which is distributed over 

 the entire surface of the cerei:)ellum, slower potential 

 oscillations have also been oljserved in both anes- 

 thetized and decerebrate animals. Potential oscilla- 

 tions at 8 to 12 per sec. have been recorded 

 primarily from the hemispheral portions of the cere- 

 l)ellum of animals under barbiturate anesthesia (81, 

 143, 320, 328, 329, 342, 363). Since these low fre- 

 quency rhythms disappear upon transection of the 

 mesencephalon, it is concluded that they are due to 

 the arrival of corticofugal discharges from the cere- 

 brum. In decerebrate animals, prepared with ex- 

 treme care and maintained in the best condition, an 

 additional variety of slow potential oscillations of 

 approximately 20 msec, in duration is obser\ed at 

 the cortical surface (214, 239, 240). These latter 

 waves appear to differ in origin from the fast rhythm, 

 but their source remains uncertain. 



At the low end of the frequency spectrum, it has 

 recently been observed that sustained d.c. shifts of 

 potential occur at the cerebellar surface as a result 

 of peripheral nerve stimulation (5). The.se negative 

 shifts endure for i to 3 sec. after single shocks to 

 peripheral nerve, are enhanced iiy local strychnine 

 and depressed by local pentoijarbital. Their signifi- 

 cance remains obscure. The phenomenon may be the 

 same as that recorded many years ago by Beck & 

 Bikeles (19, 20) using galvanometric recording. 



ACTIVITY PATTERNS IN CEREBELLAR NEURONS. SinCC 



the introduction of techniques permitting the ob- 

 servation of activity in single neurons, information 

 about cerebellar neurons has grown less rapidly than 

 one might have expected. This is in part due to the 

 technical diflSculties involved in penetrating and 

 holding single neurons in the pulsating cerebellum, 

 and in part due to sensitivity of the cerebellar cortex 

 to depressing influences mentioned above. 



The first attempts at examining single unit activity 

 were only partially successful in that the identity of 

 the units recorded could not be surely established. 

 Nevertheless, Brookhart el al. (51), utilizing small 

 wires inserted into the vicinity of Purkinje cells, 

 recorded extracellular action potentials which they 

 believed to originate from Purkinje cells. In de- 



cerebrate animals, these units showed a rather high 

 level of spontaneous activity, discharging at fre- 

 quencies ranging over wide limits, the majority fall- 

 ing into the range of 70 to 80 per sec. This 

 spontaneous activity was characterized by random 

 intermittency, discharges occurring in groups sepa- 

 rated b\ silent intervals. The factors controlling the 

 resting discharge and the intermittency of firing could 

 not be elucidated, although similar behavior was 

 recorded from units in surgically isolated areas of 

 the cortex. The units could be caused to fire and 

 could be augmented or inhibited in their activity by 

 impulses originating in the cerebral cortex or in 

 peripheral receptors. Intense afferent activity, or 

 locally applied strychnine, initiated convulsive dis- 

 charges which appeared to be self-terminating at 

 frequencies of 400 to 500 per sec. By means of the 

 same technique, it was later (52) shown that both 

 the unit and wave activity was localized to the 

 Purkinje-granule layer, and that the spike and wave 

 activity were differentially sensitive to ischemia and 

 anesthetics. The cerebellar units are also responsive 

 to polarization with constant currents according to 

 the rule that current flow oriented in the dendrito- 

 axonal axis of the Purkinje cells nearest the electrode 

 tip increased discharge; current flowing in the axo- 

 dendritic direction reduces discharge; and current 

 flowing parallel to or at right angles to the dendritic 

 tree has no influence on discharge (49, 50). 



While it remains true that information from intra- 

 cellular recordings continues difficult to obtain, 

 enough observations of this type have appeared to 

 establish the fact that Purkinje cells are, in some 

 respects, like other neurons and, in other respects, 

 show peculiar properties (54, 55, 138, 139, 343). 

 Observations of the most importance have been 

 made by Granit & Phillips. These investigators have 

 recorded both intra- and extracellularly from neurons 

 which several lines of evidence identify as Purkinje 

 cells. The general pattern of activity was the same 

 as that observed previously with extracellular wire 

 electrodes (51). They find the discharge of the cell 

 to be preceded by a prepotential which originates at 

 some distance from the recording site. Enough intra- 

 cellular recordings have been obtained to indicate 

 that the prepotential is generated by a mechanism 

 diflferent from the action potential and that cessation 

 of cell firing may be accompanied by hyperpolariza- 

 tion. These facts align the Purkinje cell with spinal 

 cord cells (82), cells of the cerebral cortex (260) and 

 the peripheral stretch receptor of the crayfish (176). 

 On the other hand, cessation of activity in Purkinje 



