In the Light of Evolution Volume VII: The Human Mental Machinery (2014) / Chapter Skim
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4 Similarity in Form and Function of the Hippocampus in Rodents, Monkeys, and Humans--Robert E. Clark and Larry R. Squire
4 Similarity in Form and Function of the Hippocampus in Rodents, Monkeys, and Humans--Robert E. Clark and Larry R. Squire
Pages 59-74
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From page 59... ...
We then recount the difficult road that was traveled to develop an animal model of human memory impairment, a matter that also turned on questions about similarities and differences between humans and other primates. We then describe how the insight that there are multiple memory systems helped to secure the animal model and how the animal model was ultimately used to identify the neuroanatomy of long-term declarative memory (sometimes termed explicit memory)
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From page 60... ...
The expectation that the study of experimental animals should yield insights into the organization of human memory is certainly reasonable when considered in the light of evolution and evolutionary theory. Indeed, the central idea behind the study of nonhuman mammals is the notion that what can be learned about mammalian behavior and mammalian brains can improve understanding of the human brain and the human condition.
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From page 61... ...
The more anterior fissure retained the name hippocampal fissure, whereas the more posterior fissure was renamed by Huxley as the calcarine sulcus because the calcar avis, or hippocampus minor, is, in fact, formed by the deep inward penetration of the calcarine sulcus (Huxley, 1861a)
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From page 62... ...
Eventually, with the consent of the family, the surgeon Scoville attempted to relieve the seizures with an experimental surgical intervention that involved resecting the medial aspect of the temporal lobe bilaterally. Subsequently, MRI scans showed that the lesion was bilaterally symmetrical and included the medial temporal polar cortex, virtually all the entorhinal cortex and amygdaloid complex, and the anterior half of the intraventricular aspect of the hippocampal formation [i.e., dentate gyrus (DG)
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From page 63... ...
. In short, it was clear from the work carried out during the 1960s that the behavioral impairments observed in rats with hippocampus lesions did not provide an adequate description of the memory impairment seen in humans with hippocampal damage.
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From page 64... ...
, or they were tasks that animals could learn as a skill even if humans tended to learn the task by memorizing the material. Establishing an animal model of human memory impairment would require developing tasks for animals that assessed the same kind of memory that is impaired in humans after medial temporal lobe damage.
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From page 65... ...
A key advance in establishing a model of human medial temporal lobe amnesia was the development of one-trial memory tests for the monkey. In 1974, Gaffan suggested that many tests of memory in animals with hippocampal damage might not be similar to the tests that reveal memory impairment in patients.
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From page 66... ...
, documented the successful establishment of an animal model of human medial temporal lobe amnesia. The DNMS task with trial-unique stimuli was subsequently adapted for use with rats (Mumby et al., 1990)
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From page 67... ...
. ORGANIZATION OF LONG-TERM DECLARATIVE MEMORY Work in the experimental animal during the past three decades used these tasks to identify a system of anatomically connected structures in the medial temporal lobe that, when damaged, produce memory impairment like the impairment first revealed by the study of H.M.
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From page 68... ...
. The major cortical components of the medial temporal lobe are highlighted [perirhinal cortex (red)
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From page 69... ...
The hippocampus, defined here as the DG, CA3, CA1, and subiculum (S) , is anatomically situated to receive highly processed information from widespread neocortical regions through three temporal cortical areas, the entorhinal, perirhinal, and parahippocampal cortices (in the rat, the term postrhinal cortex replaces the term parahippocampal cortex)
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From page 70... ...
CHALLENGE TO THE ANIMAL MODEL AND TO CROSS-SPECIES COMPARISONS As discussed earlier, during the 1960s and early 1970s, the development of an animal model of human memory and human memory impairment was challenged by the fact that animals could use nondeclarative memory to solve some memory tasks that humans typically approached using declarative memory. It therefore became important to understand under what conditions this occurs and to identify what kind of memory is used in each case.
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From page 71... ...
To address this question, patients with large lesions of the medial temporal lobe, and essentially no residual declarative memory, were given extended training on the concurrent discrimination task over a period of several weeks (Bayley et al., 2005)
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From page 72... ...
The acquired knowledge was rigidly organized, and performance collapsed when the task format was altered. The findings indicate that humans possess a robust capacity for gradual trial-and-error learning that can operate outside awareness for what is learned and independent of the medial temporal lobe.
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From page 73... ...
. In summary, the development of a model of human memory and human memory impairment in the monkey and rat is a success story, and the work has provided important insight into the anatomy and organization of mammalian memory.
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