ELECTRICAL STIMULATION OF THE HIPPOCAMPUS IN MAN 



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ball electrode (i mm in diameter) was slipped over 

 the anterior portion of the hippocampus, the walls 

 of the temporal horn keeping the electrode and its 

 insulated flexible lead in place. A second electrode 

 of the same type was placed over the superior surface 

 of the hippocampus about 2 or 3 cm behind the first. 

 Other electrodes were placed over the surface of the 

 lateral aspect of the exposed temporal cortex in front 

 of and behind the cut, and over the exposed frontal 

 and parietal lobe. Still other electrodes were slipped 

 under the orbital frontal cortex, the temporal pcjle, 

 the uncus, the anterior and the posterior part of the 

 hippocampal, the fusiform convolutions, or both of 

 the last two structures. Scalp electrodes had been 

 secured over the contralateral hemisphere. 



This arrangement was devised in order: a) to 

 ensure that the electrodes in the depth were actually 

 in contact with the superior surface of the hippo- 

 campus with but little disturbance of the brain in its 

 immediate proximity; b) to record the spontaneous 

 acti\-ity of the hippocampus simultaneously with 

 that of the cortex of the hippocampal gvrus, temporal 

 pole, uncus and other regions of the brain when their 

 connections were still intact; and c) to collect data 

 on the subjective and objective phenomena evoked 

 by electrical stimulation of the hippocampus in 

 conscious patients. 



The stimuli used were 50 per sec. square pulses of 

 3 msec, duration at 3 to 4 v. (occasionally 6 to 10 

 v.) applied through the electrodes placed on the 

 hippocampus for periods from 2 to 10 sec. In contrast 

 to other workers Pampiglione & Falconer did not 

 attempt to establish 'threshold values' for either 

 electrical discharges or clinical phenomena as their 

 aim was to evoke clinical responses immediately 

 without preliminary alteration of the 'excitability' 

 of the area. All 17 patients were suffering from 

 .seizures deemed to be of temporal lobe origin and 

 were going to be submitted to temporal lobectomy. 

 Each one had shown over a period of several months 

 to several years definite EEG abnorinalities mainly 

 in the temporal regions. In each patient stimulation 

 of the hippocampus was performed at least twice, 

 without displacing the electrodes, the intervals be- 

 tween stimulations varying from 5 to 20 min., with a 

 total of 53 stimulations. The temporal lobe later re- 

 moved in one piece, including the uncus and the 

 anterior 3 to 4 cm of the hippocampus, was studied 

 histologically by Cavenagh & Meyer (2). 



The clinical and electrographic features varied a 

 great deal from one patient to another and even in 

 the same patient for similar parameters of stimula- 



tion. On no occasion did a major seizure occur even 

 when 10 V. were applied. No constant relationship 

 was found between the duration and pattern of the 

 electrical changes and the type and duration of .sub- 

 jective and objective clinical phenomena. Clinical 

 phenomena closely similar to the patient's spontane- 

 ous aura or attack were evoked on some occasions, 

 including 'peculiar sensations,' complex hallucina- 

 tions, apparent confusion and speech disturbances. 

 On other occasions the evoked clinical phenomena 

 were of a kind apparently different from the patient's 

 spontaneous manifestations. Hallucinations of taste 

 and smell occurred only once. But often there was a 

 loss of contact with the patient who, for a few seconds 

 up to over i min., was unresponsive to sensory and 

 verbal stimuli and subsequently had amnesia for 

 this period. Sometimes no clinical changes were 

 noticed either objectively or subjectively in spite of 

 prolonged electrical storms being induced, and at 

 other times the clinical phenomena outlasted the 

 electrical changes recorded. 



The distribution of the electrical discharges was 

 less variable and on no occasion were gross changes 

 .seen after hippocampal stimulation in the orbital 

 and lateral frontoparietal cortex or in the contra- 

 lateral temporal scalp record. Often the discharges 

 were limited to the areas of one or the other, or of 

 both, electrodes placed over the hippocampus. The 

 temporal pole, the uncus, the hippocampal and 

 fusiform convolutions were also commonly involved 

 in the discharges either with or without participa- 

 tion of the anterior half of the lateral aspect of the 

 temporal cortex. On the other hand temporal regions 

 on the lateral aspect behind the level of the cortical 

 incision were less often involved. 



It is interesting to note that, although the clinical 

 phenomena elicited by Painpiglione & Falconer (15, 

 16) with this technique were numerous in compari- 

 son with the reports of other authors, there was a 

 considerable variability not only from one patient 

 to another but even in the same patient when stimu- 

 lation was repeated without displacing the electrodes 

 and without alteration in the parameters of the 

 stimulus. In a second report on their experiinents, 

 Pampiglione & Falconer (16) emphasized that, in 

 contrast with the observations reported in animals, 

 electrical stimulation of the hippocampus in man 

 was never accompanied or followed by genital 

 sensations, sexual phenomena, tactile sensations, 

 gross behavioral changes, rages, or prolonged tonic 

 or clonic movements. 



In contrast with the extreme variabilitv of the 



