Neurophysiology — Philip Bard 



the interaction of reflexes and of the rela- 

 tion of various receptors to reflex motor 

 acts. The existence of self-Hmiting activity 

 in reflex action has been recognized but 

 much of importance remains to be discov- 

 ered concerning the mechanisms involved. 

 The discovery by Kuffler of the control 

 of muscle spindle discharge by the small 

 fiber component of the ventral roots has 

 added substantially to our present concepts 

 of how the central nervous system reg- 

 ulates the tonic and phasic activities of 

 skeletal muscle. Our understanding of the 

 supraspinal control of segmental reflexes 

 was greatly expanded by Magoun's elucida- 

 tion of bulbar and brain stem areas which 

 exert excitatory and inhibitory influences at 

 the spinal level. Considerable progress has 

 been made in determining the cerebral and 

 cerebellar control of these areas. In this 

 connection it should be noted that the sig- 

 nificance of the so-called suppressor bands 

 of the cerebral cortex is by no means clear. 

 It is possible that in certain instances the 

 inhibitory effects evoked from them were 

 conditioned by the state of anesthesia. In 

 general it can be said that many stimula- 

 tion experiments should be repeated, if pos- 

 sible, without the complication of general 

 anesthesia. 



5. Electrophysiological Analyses of Cere- 

 bral Organization. These are of relatively 

 recent origin and constitute a large frac- 

 tion of current studies of the brain. The 

 actual methods used have been of several 

 kinds and have been directed toward some- 

 what different ends. Except for the well 

 known technique of electroencephalo- 

 graphy each of these methods involves the 

 recording of electrical changes induced by 

 stimulation at the periphery or at a dis- 

 tance within the central nervous system. 

 Physiological neuronography, introduced 

 by Dusser de Barenne and McCulloch, is 

 based on evidence that the local applica- 

 tion of strychnine to a gray mass causes 

 large sudden voltages (strychnine spikes) 

 to appear in all places where axons of cells 

 situated in the strychninizcd region ter- 

 minate. The method has been used ex- 

 tensively to determine neuronal connec- 

 tions and it has doubtless provided some 



useful information regarding intracortical 

 connections and connections between cor- 

 tical and subcortical regions. The assump- 

 tion, widely held, that where and if im- 

 pulses set up by strychnine cross synapses 

 they become asynchronous and so undetec- 

 table may be questioned, and if it should 

 prove even partly erroneous many of the 

 conclusions that have been drawn will have 

 to be revised. In any case, activation of 

 neurons by strychnine appears to have the 

 advantage over electrical stimulation that 

 it does not set up antidromic conduction 

 and does not produce an electrical artefact 

 that may make electrical recording difficult 

 or impossible. Another relatively new pro- 

 cedure is the determination of the central 

 representations of sensory modalities by 

 recording potentials evoked by appropriate 

 stimulation of sensory surfaces. The ap- 

 plication of this method has made it pos- 

 sible to map in great topographical detail 

 the major sensory areas of the cerebral cor- 

 tex, to demonstrate that several sensory mo- 

 dalities have specific representations in the 

 cerebellar cortex, and to show that tactile 

 sensibility has a detailed topographical pat- 

 tern of representation in the thalamus and 

 the dorsal column nuclei. The method has 

 led to some unexpected results which will 

 doubtless prove to be of importance. The 

 discovery that the tactile, visual and audi- 

 tory systems have a definite cerebellar rep- 

 resentation is one of these. Another is that 

 there are two complete and separate sen- 

 sory projection areas for touch, vision and 

 audition in the cerebral cortex of mammals. 

 The functional significance of these two 

 facts remains to be determined. 



6. Anatomical and Physiological Correla- 

 tions. It is well recognized that many 

 neuroanatomical facts are devoid of func- 

 tional significance. For example, there are 

 conspicuous fiber tracts within the central 

 nervous system to which no function can 

 be assigned. It is desirable that modern 

 methods of neurophysiology be employed 

 in attempts to dispel this ignorance. On 

 the other hand, physiological studies have 

 revealed the existence of functional con- 

 nections for which there appears to be no 

 known anatomical basis. Thus the two dis- 



