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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



but could not determine that they were due to direct 

 connections. On the other hand, secondary con- 

 nections, via the mammillary body, are well estab- 

 lished (27, 33, 43, 82, 87, III), and there is evidence 

 for connections to the anteromedial, anterodorsal and 

 anteroventral nuclei, as well as to the intralaminar 

 nuclei (45). Rose & VVoolsey (94-96) demonstrated 

 the relationship between rostral thalamus, cingulum 

 and rhinencephalon, and found that removal of the 

 rhinencephalon, striatum and amygdala led to de- 

 generation of the mid-line and intralaminar nuclei of 

 the thalamus. Powell (85) reported a case of com- 

 plete surgical hemidecortication in which, however, 

 the mid-line and intralaminar nuclei, as well as the 

 nucleus limitans and the parafascicular nucleus, 

 showed no evidence of any change 24 days post- 

 operatively, but the anterior nuclei showed extreme 

 degeneration. The fornix was apparently spared. The 

 anterior nuclei of the thalamus (particularly the 

 anteromedial and anteroventral) are thus functionally 

 related to the hippocampus, and there also may be 

 connections, perhaps secondarily, with intralaminar 

 nuclei and mid-line nuclei. Stimulation of the hippo- 

 campus evokes responses in the anterior, mid-line and 

 intralaminar nuclei, and stimulation of these nuclei 

 evokes recruiting responses in the hippocampus itself 

 as well as in the neocortex. In the guinea pig, stimula- 

 tion of the precommissural fornix (50) also leads to 

 recruiting responses. 



OTHER AREAS. Direct connections to the mammillary 

 body are well known. The main region of termination 

 is the medial mammillary nucleus (30, 52). Connec- 

 tions with other parts of the hypothalamus, besides 

 the mammillary body, are not certain although there 

 seems to be a good deal of evidence that a few fibers 

 of the fornix leave it before it reaches the mammillary 

 region. Some fibers probably continue from the fornix 

 directly into the tegmentum where Nauta (82) and 

 Guillery (52) have seen bouton degeneration, and 

 Green & Adey (45) have found short-latency responses 

 in a zone between the red nucleus and the substantia 

 nigra. 



There are numerous and important connections 

 in the septal area. Many of these are efferent, par- 

 ticularly to the medial septal nuclei; but in this region 

 there is a vast convergence of fibers extremely difli- 

 cult to unravel. Ramon y Cajal's (90) views on the 

 structure and connections of the septum lucidum and 

 on its relationship to the hippocampus are given in 

 detail in a recent translation. It seems unlikely that 

 verv much more mav be added bv direct anatomical 



studies on normal material. Daitz & Powell (30) found 

 that division of the fimbria resulted in complete 

 atrophy, or shrinkage, of the cells of the ipsilateral 

 medial septal nucleus and partial degeneration of the 

 nucleus of the diagonal band, but that additional in- 

 volvement of the fornix or stria terminalis, that is to 

 say the dorsal portions of the fornix, did not result in 

 any intensification of this degeneration. Nor did they 

 find that degeneration occurred in the septum follow- 

 ing destruction of the entorhinal cortex or amygdala. 

 Powell & Cowan (88) found that division of the dorsal 

 fornix and fimbria results in complete atrophy of the 

 descending column of the fornix, but that lesions of the 

 fimbria resulted in only slight degeneration of the 

 descending column of the fornix although there was a 

 complete lass of precommissural fibers in the septum 

 and degeneration of the medial cortical hypothalamic 

 tract. They concluded that most of the efTerent fibers 

 of the fimbria ended in the hypothalamus anterior to 

 the maminillary nuclei. They believed that the axons 

 of the pyramidal cells of field hi, which would be the 

 medial field of pyramidal cells in a section through 

 the dorsal hippocampus, turn medially in the alveus 

 into the dorsal fornix, while those of cells in fields 

 h-2 and hs, or laterally placed cells, have axons which 

 bend laterally toward the fimbria. Thus, they con- 

 ceived that the lateral portions of the hippocampus 

 project chiefly to the septum and hypothalamus, 

 whereas the medial portions project toward the mam- 

 millary body. 



Although the physiological evidence for aflferents to 

 the hippocampus from the septum seems indisput- 

 able, the precise anatomical pathways concerned are 

 as yet by no means clear. Gerebtzoff (39) found 

 Marchi degeneration extending backward in the 

 colonne horizontale following lesions in the septum, and 

 retrograde degeneration has been described by Morin 

 (79) using Marchi methods, and by Daitz & Powell 

 (30) and Powell & Cowan (88) using retrograde cell 

 degeneration (Nissl) and fiber loss (Bodian) methods. 

 The latter authors found no sign of cell degeneration 

 in the hippocampal pyramids following section of the 

 fornix. They explained this by .supposing that the re- 

 current collateral fibers of the pyramidal cell axons 

 maintain the activity of the pyramidal cells even 

 though the more distal part of the axons were severed. 

 Some of the Marchi degeneration, however, could be 

 explained on the basis of afferent fibers in the fimbria 

 and alveus. Ramon y Cajal (90) and many of the 

 older authors described afferents from the septal area 

 to the hippocampus, and Ramon y Cajal (90) spe- 

 cificalh' indicates that these afferents are not of 



