CHAPTER IX 



Brain potentials and rhythms — introduction 



A. FES SARD College de France, Paris, France 



CHAPTER CONTENTS 



General Nature of Brain Potentials 

 Special Characteristics of Brain Potentials 

 Functional Significance of Brain Potentials 

 Microphysiological Studies 

 Macrophysiological Studies 



but an introduction to this chapter may better take 

 into account more fundamental features of this field 

 of research by considering broadly the three questions 

 of the general nature, the special characteristics and 

 the functional significance of brain potentials and 

 rhythms, each special aspect being dealt with in de- 

 tail in subsequent chapters. 



FOR OBVIOUS REASONS, the stuclv of brain potentials 

 and of their rhythms is by far the most complicated 

 task that has ever been proposed to electrophysi- 

 ologists. It is therefore not surprising that its develop- 

 ment has been relatively slow. In the period from 1875 

 to 1913, the names of Caton C'S), Fleischl 

 von Marxow (25), Danilewski (19), Beck & Cybulski 

 (7) and Prawdicz-Neminsky (44, 45) stand out among 

 the few pioneers who experimented on animals, 

 preceding the epoch-making discovery of brain waves 

 in man by Hans Berger in 1924 [first published in 

 1929 (8)]. As a matter of fact, not before the end of 

 the first third of this century did cerebral electro- 

 physiology truly enter the regular scope of neuro- 

 physiological research with the first works of Fischer 

 (24), Kornmuller (35, 36), Bartley (6), Bishop (9), 

 Adrian & Matthews (2), Gerard et at. (26, 27), Wang 

 C50), Bremer (10), Gozzano (29), Adrian (i) and 

 Jasper (31). During this same period, clinical elec- 

 troencephalography was developing vigorously and 

 furnishing itself results important for the compre- 

 hension of cerebral mechanisms. Perhaps in no other 

 field of neurophysiology is there such a reciprocity 

 of relations between the findings of investigation on 

 experimental animals and those of clinical observa- 

 tions. This circumstance has contributed to the par- 

 ticular character of cerebral electrophysiology today; 



GENER.'VL N.4TURE OF BR.AIN POTENTI.^LS 



The question of the nature of brain potentials 

 leads us back to the preceding chapters on neuron 

 physiology, for there is nothing essentially new appear- 

 ing in the ijrain of a bioelectrical nature, nothing 

 not having a physicochcmical basis common to all 

 neurons. The fundamental phenomena of neuronal 

 activity, i.e. brief all-or-nothing spikes, graded slow 

 waves, potential gradients of ill-defined duration, 

 have been well recognized as the sole components of 

 brain potentials. On the other hand, conduction of 

 impulses along fibers, transmission of excitation or 

 inhibition across synapses, electrotonic spread and 

 "ephaptic' interactions, and finally rhythmic genera- 

 tion of potentials are the general kinetic operations 

 from which all attempts to explain the integrated ac- 

 tivities of the brain must start. 



Detection of these elementary processes within the 

 brain and description of their quantitative parameters 

 as compared to those of neurons belonging to other 

 structm-es (such as the spinal cord, ganglia in verte- 

 brates or invertebrates, peripheral sensory neurons) 

 are the tasks that have been and are still being carried 

 out by electrophysiologists since the pioneer work of 

 Renshaw et al. (46) who introduced the highly re- 

 warding microelectrode technique in brain physiology. 



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