CHAPTER L V 1 1 



Electrical stimulation of the hippocampus in man 



G. PAMPIGLIONE* 

 MURRAY A. FALCONER 



Guy's-Maudsley Neurosurgical Unit and The Institute of 

 Psychiatry, London University, England 



A CONSIDERABLE VOLUME OF DATA has accumulated 

 in the literature on the physiology of the hippocampal 

 region since publication of the contradictory inter- 

 pretations of Ferrier (5), Spencer (23) and Ossipoff 

 (14) based on experimental work on animals. Re- 

 cently Kaada (9), Macchi {13). Gastaut (6), Cadilhac 

 (i), Green & Adey (8) and Green in the preceding 

 chapter of this work have added to our knowledge of 

 the function of the hippocampus in animals and re- 

 viewed the previous papers on the subject. 



Electrophysiological observations in man however 

 are scanty, and small groups of patients have been 

 studied without uniform technique and often with- 

 out anatomical control. The difficulty of approaching 

 the hippocampal region in man is probably the main 

 reason for the small numl)er of published reports in 

 spite of the growing interest of clinicians and neuro- 

 surgeons in the possible role of this area of the brain 

 in health and disease. 



The nomenclature of the cerebral structures in- 

 cluded in the so-called rhinencephalon of man is 

 somewhat confused in the literature [for discussion 

 see (i, 13)]. In the present review we shall make a 

 distinction between the hippocampus (Aminon's 

 horn, cornu ammonis or hippocampal formation, 

 including the gyrus dentatus) and the hippocampal 

 con\'olution (gyrus hippocampi, fifth temporal con- 

 \olvuion or gyrus uncinatiis).' The hippocampus 

 forms the floor of the temporal horn of the lateral 

 ventricle and the hippocampal fissure separates the 



* Present address: The Hospital for .Sick Children, London, 

 England. 



' 'Hippocampal convolution' as used in this chapter is equiv- 

 alent to 'entorhinal area' as used by Green in the preceding 

 chapter — [Ed.j. 



hippocampus proper (including the subicular region) 

 from the hippocampal convolution. Ontogenetically 

 both the dorsal and the rostral hippocampus in man 

 undergo very early regressive changes and these 

 structures have probably only vestigial importance 

 after fetal life, in contrast to certain animals where 

 the olfactovegetative association areas remain ex- 

 tensi\e (12, 13). The uncus is the rostral portion of 

 the hippocampal convolution and is therefore sepa- 

 rate from the hippocampus proper. The vague term 

 of hippocampal region will be used in this paper to 

 include the hippocampus, the hippocampal gyrus 

 and the uncus. 



The few observations upon the effects of electrical 

 stimulation of the hippocampal region in man in the 

 literature fall into three main groups according to 

 the approach used. 



a) .Stimulation of the hippocampal convolution, 

 uncus, tip of the temporal lolje and the region of the 

 amygdaloid complex has been undertaken in the 

 intact brain by applying the stimulating electrodes 

 to the cortex of the inferior surface of the temporal 

 lobe after it had been lifted slightly from the floor of 

 the middle fossa. This approach has been used by 

 Chapman et al. (3), Libenson et al. (11), Kaada (9), 

 Sloan (■/ al. (22), Kaada & Jasper (10), Glusman 

 et al. (7), Pool (21), Chapman et al. (4) and Penfield 

 & Jasper (20). 



/)) The proximal end of the hippocampus has 

 been stimulated during the operations of hemi- 

 spherectomy or temporal lobectomy after most of 

 the temporal cortex had been remo\ed. The stimu- 

 lating electrodes were placed either on the cut 

 surface of the hippocampus or on its superior surface. 

 Workers using this technique include Penfield & 



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