![]() ![]() These authors managed to integrate all these seemingly disparate observations into a coherent theoretical framework organized around the concept of place cells as the cellular basis for representation of space as well as events and experiences associated with space. This emphasis on HF was strengthened by a large body of existing data reporting the beautiful morphological simplicity of HF and its intrinsic organization (Blackstad, 1956, 1958 Haug, 1976 Hjorth-Simonsen, 1971 Hjorth-Simonsen & Jeune, 1972 Lorente de Nó, 1934 Ramón y Cajal, 1893), the first description of the spatially modulated “place cell” (O'Keefe, 1976 O'Keefe & Dostrovsky, 1971), the phenomenon of long-term potentiation (Bliss & Lømo, 1973), all culminating in the very influential book in which O'Keefe and Nadel proposed the theory of the hippocampus as a cognitive map (O'Keefe & Nadel, 1978). ![]() Irrespective of the fact that the lesions included several different brain structures aside HF bilaterally, the field quickly zoomed in on HF as the likely most critical structure underlying episodic memory (Milner, Squire, & Kandel, 1998). The lesions included a substantial part of the hippocampal formation (HF), the amygdala and the parahippocampal region (PHR), in particular the entorhinal cortex (EC) and perirhinal cortex (PER) (Annese et al., 2014 Augustinack et al., 2014 Scoville & Milner, 1957). The focus on the medial temporal lobe as being critically involved in episodic memory was essentially initiated by the influential paper on patient HM, reporting the devastating anterograde amnesia as the result of bilateral resections of the antero-medial portions of the temporal lobe. ![]() Research on memory suffers from a comparable threat in that well-established theories might become difficult to adjust to encompass new insights. This same robustness, however, provides a potential threat in that memories might become harder to change and thus our behavior may become guided by concepts that are no longer an adequate representation of the current situation. The efficacy of our memory system to make accurate predictions about future events depends on the relative robustness of our stored memories. Previous experiences with a high similarity become eventually stored as generalized concepts or schemes, which are being updated with new experiences. The ability to store and recall information comes of use in a variety of daily behaviors, and the likely most important role is for us to make predictions based on previous experiences. ![]() Memory is an important capacity of the brain and has intrigued scientists ever since they started to study the brain. This thus indicates that the current connectional model of the parahippocampal region as part of the medial temporal lobe memory system needs to be revised. We suggest that entorhinal inputs provide the hippocampus with high-order complex representations of the external environment, its stability, as well as apparent changes either as an inherent feature of a biological environment or as the result of navigating the environment. In contrast, here we argue that the connectivity matrix emphasizes the potential of substantial integration of cortical information through interactions between the two entorhinal subdivisions and between the perirhinal and postrhinal/parahippocampal cortices, but most importantly through a new observation that the postrhinal/parahippocampal cortex projects to both lateral and medial entorhinal cortex. In this scenario, the lateral entorhinal cortex and the perirhinal cortex are connectionally associated and likewise the postrhinal/parahippocampal cortex and the medial entorhinal cortex are partners. The concept of two entorhinal areas, the lateral and medial entorhinal cortex, belonging to two parallel input–output streams mediating the encoding and storage of respectively what and where information hinges on the claim that a major component of their cortical connections is with the perirhinal cortex and postrhinal or parahippocampal cortex in, respectively, rodents or primates. In this review, we aim to reappraise the organization of intrinsic and extrinsic networks of the entorhinal cortex with a focus on the concept of parallel cortical connectivity streams. ![]()
0 Comments
Leave a Reply. |