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Elissa M. Aminoff, Nurit Gronau, Moshe Bar; The parahippocampal cortex mediates both spatial and non-spatial associative processing. Journal of Vision 2005;5(8):907. doi: 10.1167/5.8.907.
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The parahippocampal cortex (PHC) has been implicated in several cognitive processes, most prominently in place-related processing, in episodic memory, and, recently, in processing contextual associations (Bar and Aminoff, 2003). These seemingly independent processes have the unifying characteristic of dependence on associations. Consequently, we proposed that the PHC mediates general processing of associations, regardless of their use in navigation, memory or context. A place within the PHC, termed the parahippocampal place area (PPA), has specifically been implicated in processing space and landmark-related information. Because the representation of a landmark can be considered an associative conjunction of individual constituents, we re-interpreted place-related activity in the PHC as reflecting spatial associative processing. We tested this idea here by creating novel associations among novel visual patterns that had no prior association with any place or concept. Subjects were trained to associate each of the studied patterns with one of three conditions: Spatial (3 items always appearing together in the same spatial configuration), Non-Spatial (3 items in random locations), or No-Association (an item appearing alone in a random location). The studied items were presented individually to subjects while using fMRI. All associated items activated the PHC: items associated with spatial contexts activated the posterior PHC whereas items associated with non-spatial contexts activated the anterior PHC. This replicates the hierarchical organization we have reported previously using pictures of real objects. Furthermore, a PPA localizer scan revealed that photographs of places (e.g., a street) elicited activation confined to the posterior PHC, as the spatial, meaningless, patterns we used. This study provides evidence that the PHC has a global role of processing associations in general, with a hierarchy depending, at least in part, on degree of spatial specificity.
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