THE HIPPOCAMPUS 



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RM 

 LM 

 LF 



R F 

 R M 



L M 

 L F 



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AFTER (cat) 



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LESION IN SEPTUM (robbit) 



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DESTRUCTION OF MAMMILLARY BODY (rabbit) I SEC. 



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FIG. 6. Effect of lesions of the brain 

 on cortical and hippocampal arousal. 

 RF, right frontal cortex; RM or RMC, 

 right motor cortex; LM or LMC, left 

 motor cortex; LF, left frontal cortex; 

 R. Hip., right hippocampus; L. Hip., 

 left hippocampus; OB, olfactory bulb. 

 In first two records it is shown that re- 

 moval of the hippocampus does not 

 entirely eliminate cortical 'arousaP re- 

 sponse which follows stimulation of 

 intralaminar thalamic nuclei. In third 

 record it is seen that, after lesion in dorsal 

 septal area (destroying much of septum 

 above anterior commissure, precom- 

 missural fornix and part of rostral end 

 of cingulate area), there was no hippo- 

 campal arousal to an olfactory stimulus. 

 While this negative result is not strik- 

 ing, it should be emphasized that these 

 rabbits were the only ones in which no 

 hippocampal arousal could be evoked 

 and it seems to correlate well with re- 

 sults of section of dorsal fornix (includ- 

 ing precommissural fornix fibers). In 

 Itisl record effect of cutting left dorsal 

 fornix in decorticate animal is seen. 

 Note that response is abolished on ipsi- 

 lateral side. [From Green & Arduini 

 (46).] 



rhythm could also he induced by stimulating the 

 reticular activating system of Moruzzi & Magoun 

 (81) from the midbrain tegmentum and from points 

 extending through the lateral hypothalamus to the 

 septum and back into the hippocampus. No theta 

 rhythm, however, was ever induced by stimulation 

 of the hippocampus directly. The theta rhythm could, 

 however, be traced forward from the hippocampus 

 into the fornix, mammillary body, mammillothalamic 

 tract, toward the anterior thalamus, and it was felt 

 that it could also probably be recorded from the 

 habenulopeduncular tract, although it was conceiv- 

 able that this was a volume conduction effect. They 

 found that destruction of the mammillary body did 

 not block the theta rhythm in the hippocampus and 



that stimulation of the mammillary ljod\ did not in- 

 duce it. The theta rhythm was not blocked by lesions 

 in the amygdala nor by removal of the entorhinal 

 cortex. This latter point has been disputed by Car- 

 reras et al. (26) who were unable to find the theta 

 rhythm after the entorhinal cortex was removed, but 

 it has been confirmed on the other side by Adey el al. 

 (2). Ricci & Sutin (personal communication) also 

 stated thay they ob-served the theta rhythm after the 

 entorhinal cortex had been remo\ed but noted that 

 before it reappeared a period of shock frequently 

 ensued in their animals. Green & Arduini (46) con- 

 cluded that afferents reached the hippocampus by 

 way of the reticular activating system, hypothalamus 

 and septum and that efTerents left it by way of the 



