■2.=s6 



HANDBOOK OF PHYSIOLOGY -^ NEUROPHYSIOLOGY 1 



Among those who early worked along; this line, let us 

 mention Moruzzi and several collaborators of his 

 school (42 and many subsequent papers), Jung et al. 

 (34), Amassian (5), Li & Jasper (38), Albe-Fessard 

 & Buser (3, 4), Tasaki and colleagues (49), Rose & 

 Mountcastle (48) and Phillips (43). These workers 

 have started a probably long-lasting and fruitful era 

 of intensive microexploration of cerebral structures. 

 For the identification and analysis of single unit ac- 

 tivities within the brain, knowledge already acquired 

 from more accessible structures, particularly from 

 spinal motoneurons, can be of great help (see Chapters 

 III and X of this work). 



In another direction, leading down to the molecular 

 le\el, are the investigations of those interested in bio- 

 physical and biochemical mechanisms, as well as 

 drug actions, that are related to, or interfere with, 

 electrical activities of brain tissue. The way in which 

 these activities depend upon metabolic factors, circu- 

 latory and respiratory conditions, ionic and hormonal 

 content of the milieu interieur, is far from being exactly 

 known. An alteration of the resting potentials is 

 assumed to be the basis of some ionic and drug actions. 



SPECI.\L CH.'^RACTERISTICS OF BRAIN POTENTIALS 



Brain potentials, apart from the common aspects 

 they share with other biopotentials, have special 

 characteristics which are related to the structure and 

 specific properties of the tissue within which they are 

 engendered. How these relations can explain the 

 different modalities of potentials encountered is the 

 central theme of the chapters constituting the present 

 subsection of this volume. A bread survey of the 

 factors involved may help to grasp the wonderful 

 complexity and dixersity of electrical manifestations 

 offered by a mammalian brain, either in its .so-called 

 spontaneous activity or under experimental condi- 

 tions including controlled stimulation. Thus we come 

 to the classical distinction between evoked potentials 

 (^considered by Chang in Chapter XII) and autogenic 

 rhythms (discussed by Walter in Chapter XI) to 

 which a transitional modality must be added, that of 

 induced rhythmical activities of temporary character 

 or after-discharges (also appearing in the chapter 

 by Chang). 



Other general distinctions within the field of brain 

 potentials will be considered below, together with 

 some of the problems confronted by the modern 

 neurophysiologist. 



FUNCTIONAL SIGNIFICANCE OF BRAIN POTENTIALS 



The third aspect is the functional significance of 

 brain potentials and their rhythms. We are not di- 

 rectly concerned here with this functional aspect 

 which will be examined in later chapters of this 

 volume. However, it is ditticult and to a certain 

 extent artificial, once a potential has been described, 

 not to speak of the link it appears to have with an 

 actual operation of the nervous system of which it 

 thus becomes a sign: projection of an afferent message, 

 interactions between central activities or emission of 

 efferent impulses. This most often invokes simple 

 questions of functional topography or chronology 

 but may also go so far as to relate to highly integrated 

 psychological processes (as will appear in Walter's 

 chapter) or to the well-defined symptoms of patho- 

 logical behavior such as those of epileptic seizures 

 (described by Gastaut in Chapter XIV) once it has 

 been recognized that reliable correlations exist be- 

 tween these phenomena and some parameter or 

 parameters of brain potentials or rhythms that have 

 initially been studied for themselves. New specific 

 aspects of brain potentials are often discovered as a 

 consequence of functional explorations of this kind. 



Let us return to the special characteristics of po- 

 tentials arising within the brain. These appear either 

 in the form of more or less durable states — potential 

 gradients and regular periodic changes — or in the 

 form of responses to direct or indirect stimuli. In 

 l)oth cases, one must clearly distinguish the micro- 

 physiological approach applying to single units from 

 the record of potentials arising within more or less 

 numerous neuronal populations. 



.\IlCROPHYSIOLOGIC.\L STUDIES 



The microphysiological approach reveals not only 

 the most common processes of neural electrogenesis 

 but al.>;o important differences between the elec- 

 trical behavior of single units. Among the various 

 types of neurons, some are more accessible than others 

 to microelectrode study. The pyramidal cells of the 

 cerebral cortex, the Purkinje cells of the cerebellum, 

 the neurons of the main sensory relay nuclei and those 

 in the midbrain reticular formation and the centrum 

 medianum of the thalamus ha\c l:)een the most care- 

 fully studied. The general shape of the neuron, the 

 distribution of synapses along its surface and the 



