The study of patients has shown that certain higher cognitive processes, such as those involved in the monitoring and the manipulation of information within working memory, depend on the integrity of both the dorsolateral frontal cortex and the medial temporal lobe memory system, as well as on their functional interaction (Petrides, 1994). Small surgical removal of the anterior temporal region, including the entorhinal cortex, is not sufficient to interrupt that fronto-hippocampal relationship. More extensive removals, however, that include a sizeable portion of the hippocampus and the surrounding parahippocampal cortex do disrupt such a fronto-hippocampal functional interaction (Petrides and Milner, 1982). Based on these data, it was postulated that the fronto-hippocampal functional interaction is not entirely dependent upon the integrity of the entorhinal cortex. To test this hypothesis, injections of tritiated amino acids were placed within individual cytoarchitectonic units of the frontal cortex, and the resulting labeling in the hippocampal region was analyzed. It was shown that the mid-dorsolateral frontal cortex, together with its medial cortical extension, is the only frontal region that sends efferent fibers, running caudally as part of the cingulum bundle, to the presubiculum, the posterior parahippocampal gyrus, as well as to the retrosplenial cortex. A light contingent of these fibers, congregating in the outermost layer of both the retrosplenium and the presubiculum, course into the molecular layer of the hippocampus proper. In complete agreement with the work with patients, these findings have confirmed the hypothesis that the mid-dorsolateral frontal cortex is closely affiliated with the hippocampal system, and demonstrated that this hodological relationship bypasses the entorhinal cortex. / Another major contribution of the present work has been to provide the first architectonic analysis of a gross morphological region, referred to as the caudomedial lobule, which receives inputs from the mid-dorsolateral frontal cortex and its medial extension. This architectonic analysis has revealed that the caudomedial lobule is nothing but the postero-ventral extension, below the splenium of the corpus callosum, of areas 29 and 30, which together form the retrosplenial cortex, and of area 23, which partly forms the posterior cingulate cortex. Among the cortical fields that comprise the postero-ventral part of the retrosplenial cortex, area 30 is the major recipient of the mid-dorsolateral frontal inputs. / By virtue of the close anatomical relation of area 30 with the mid-dorsolateral frontal cortex and its medial extension, it is suggested that this part of the retrosplenial cortex may be a critical relay-station along the dorsomedially directed fronto-hippocampal pathway. In order to validate this hypothesis, the connections of area 30 were investigated by placing injections of anterograde and retrograde tracers within the limits of this retrosplenial area. This study has demonstrated that area 30 is bi-directionally connected with and only with that part of the lateral frontal cortex that lies above the sulcus principalis, namely the mid-dorsolateral frontal cortex, along with all the structures of the posterior hippocampal region that are the recipients of the inputs from the mid-dorsolateral frontal cortex. Since the fronto-hippocampal association fiber system described in the present thesis is most probably subserving certain aspects of working memory, area 30, by virtue of its bi-directional connections with both the mid-dorsolateral frontal cortex and the posterior parahippocampal cortex, is in a privileged position to exert a major influence in working memory processing.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.42100 |
| Date | January 1996 |
| Creators | Morris, Renée. |
| Contributors | Petrides, Michael (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Neurology and Neurosurgery.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001549410, proquestno: NQ30342, Theses scanned by UMI/ProQuest. |
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