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S6-1 Topography of information flow through the parahippocampal-hippocampal circuit
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Symposium 6. Structure and function of hippocampus and parahippocampal structures.
S6-1 TOPOGRAPHY OF INFORMATION FLOW THROUGH THE PARAHIPPOCAMPAL -HIPPOCAMPAL CIRCUIT. DAVID G. AMARAL, PH.D. University of California, Davis Department USA
of Psychiatry and Center for Neuroscience
1544 Newton Ct Davis, California 95616,
Based largely on the results of clinicopathological studies of human amnesic patients, and in particular from the studies of patient H.M. who underwent bilateral medial temporal lobectomy, it is commonly believed that the hippocampus plays a central role in the formation and consolidation of long term memories. Study of these amnesic patients also make it clear that the hippocampus is not the final repository of memory since its removal does not preclude recall of memories formed years before the damage. Starting from the premise of hippocampal importance to memory, we have carded out a series of studies that are designed to determine first, where the hippocampal formation receives its sensory information i.e. what is the raw material of memory formation and second, where does the hippocampal formation send its processed information i.e. where are the putative storage sites. My presentation will provideasummaryoftheaeatudies.Ustngmodern l-lmmamicaltracingtechniques,wehavedem-thatthe entorhinal cortex of the hippocampal formation receives direct nwco&al inputs from a variety of potysensory cortical regions. The major cortical innervation originates in a -t-y cortical band made up of the perfrhinai cortex (areas 35and36)andparahippocampalcortex(areasTFandTH).Theperiminalcortexprojectsmostheavilytothe rostrolateral two-thirds of the entorhlnal cortex, and the parahippocampal cortex projects most heavily to the caudal two-thirds. The entorhinal cortex also projects back to the perirhinal and parahippocampal cortices. The entorhinal cortex, in turn, projects to the dentate gyrus, hippocampus and subiculum. We have studied the organization of erttorhinal projections to these fields in the rat and monkey and found that part of the system (the layer II projectii to the dentate gyrus and CA3) is organized in a laminar fashion whereas another pad of the system (the layer Ill projection to DA1 and the subiculum) is orga&ed in a topographic fashion. lt has also become clear from studies in the rat, that the entorhinal cortex can be divided into three regions based upon the septotemporal level (rostrocaudal in the monkey) to whiih it pro@cts. Data concerning the reciprocal connections between the enton%al cortex and other hippocampal fields will be discussed. We have also carried out a comprehensive analysis of the connectivity of the petfrhinal and parahippocampal cortices which demonstrated that these polysensoty corbces receive deciity dkfemnt complements of inputs. Unimodal associational inputs arise from somatosensory, auditory, and visual association cortices. While the majority of the input to these cortices is from visual areas, dii types of vfsual information reach the perirhinal and parahippocampal cot&es. visual object information derived from projections originating in area TE predominantly reaches the pertrhii cortex whereas visuospatiaf infomMion, arising from posterior parietal cortex and area V4, is more heavily directed to the parahippocampaf cortex. Codices identified with somatosensory processing, primarily the granular and dysgranular insular codices, project both to perirhinal and parahiqxfcampal cortkw. Auditory association cortex only pmjects to the parahippocampal cortex, par&My to area TH. The perirhinal and parahippocampal cortices receive polywwory information from ventrolateral and orbii codkzes, cingulate and retrospfenial codices, posterior parietal wrtax, and the pdymodal region of the dorsal bank of the superior temporal sulcus. All of these cortices project to parahippocampai cortex, but the predominant polymodal associational input to perirhinal cortex arises from the parahippocampal cortex and the superior temporal sulcus. Interestingly, while the parahippocampal cortex pro@cts heavily to the periminal cortex, the perirhinal cortex projection to the parahippocampal cortex is rather meager. The presentation will provide a summary of the types of information reaching the pertrhinal and parahippocampal cortices as the major source of input to the entorhinal cortex, will summarize entorhinai-hippocampal interconnections and till discuss evidence for entorhinal connections back to the neocortex. Evidence for topography of these connections and implications for parallel processing in the hippocampal system will be discussed.
Symposium 6. Structure and function of hippocampus and parahippocampal structures.
S6-1 TOPOGRAPHY OF INFORMATION FLOW THROUGH THE PARAHIPPOCAMPAL -HIPPOCAMPAL CIRCUIT. DAVID G. AMARAL, PH.D. University of California, Davis Department USA
of Psychiatry and Center for Neuroscience
1544 Newton Ct Davis, California 95616,
Based largely on the results of clinicopathological studies of human amnesic patients, and in particular from the studies of patient H.M. who underwent bilateral medial temporal lobectomy, it is commonly believed that the hippocampus plays a central role in the formation and consolidation of long term memories. Study of these amnesic patients also make it clear that the hippocampus is not the final repository of memory since its removal does not preclude recall of memories formed years before the damage. Starting from the premise of hippocampal importance to memory, we have carded out a series of studies that are designed to determine first, where the hippocampal formation receives its sensory information i.e. what is the raw material of memory formation and second, where does the hippocampal formation send its processed information i.e. where are the putative storage sites. My presentation will provideasummaryoftheaeatudies.Ustngmodern l-lmmamicaltracingtechniques,wehavedem-thatthe entorhinal cortex of the hippocampal formation receives direct nwco&al inputs from a variety of potysensory cortical regions. The major cortical innervation originates in a -t-y cortical band made up of the perfrhinai cortex (areas 35and36)andparahippocampalcortex(areasTFandTH).Theperiminalcortexprojectsmostheavilytothe rostrolateral two-thirds of the entorhlnal cortex, and the parahippocampal cortex projects most heavily to the caudal two-thirds. The entorhinal cortex also projects back to the perirhinal and parahippocampal cortices. The entorhinal cortex, in turn, projects to the dentate gyrus, hippocampus and subiculum. We have studied the organization of erttorhinal projections to these fields in the rat and monkey and found that part of the system (the layer II projectii to the dentate gyrus and CA3) is organized in a laminar fashion whereas another pad of the system (the layer Ill projection to DA1 and the subiculum) is orga&ed in a topographic fashion. lt has also become clear from studies in the rat, that the entorhinal cortex can be divided into three regions based upon the septotemporal level (rostrocaudal in the monkey) to whiih it pro@cts. Data concerning the reciprocal connections between the enton%al cortex and other hippocampal fields will be discussed. We have also carried out a comprehensive analysis of the connectivity of the petfrhinal and parahippocampal cortices which demonstrated that these polysensoty corbces receive deciity dkfemnt complements of inputs. Unimodal associational inputs arise from somatosensory, auditory, and visual association cortices. While the majority of the input to these cortices is from visual areas, dii types of vfsual information reach the perirhinal and parahippocampal cot&es. visual object information derived from projections originating in area TE predominantly reaches the pertrhii cortex whereas visuospatiaf infomMion, arising from posterior parietal cortex and area V4, is more heavily directed to the parahippocampaf cortex. Codices identified with somatosensory processing, primarily the granular and dysgranular insular codices, project both to perirhinal and parahiqxfcampal cortkw. Auditory association cortex only pmjects to the parahippocampal cortex, par&My to area TH. The perirhinal and parahippocampal cortices receive polywwory information from ventrolateral and orbii codkzes, cingulate and retrospfenial codices, posterior parietal wrtax, and the pdymodal region of the dorsal bank of the superior temporal sulcus. All of these cortices project to parahippocampai cortex, but the predominant polymodal associational input to perirhinal cortex arises from the parahippocampal cortex and the superior temporal sulcus. Interestingly, while the parahippocampal cortex pro@cts heavily to the periminal cortex, the perirhinal cortex projection to the parahippocampal cortex is rather meager. The presentation will provide a summary of the types of information reaching the pertrhinal and parahippocampal cortices as the major source of input to the entorhinal cortex, will summarize entorhinai-hippocampal interconnections and till discuss evidence for entorhinal connections back to the neocortex. Evidence for topography of these connections and implications for parallel processing in the hippocampal system will be discussed.