The relationship between hippocampus and amnesia
There is evidence of the relationship between the hippocampus and the declarative memory (Eichembaum, Cohen, 2014). For example, in patients with amnesia who have injuries in the hippocampus and their subcortical connections have selective deficits in declarative memory, but are able to distinguish new objects that are familiar to them (Giovanello et al., 2003) and in them it was also discovered that the hippocampus maintains the ability to associate objects in memory and remember contextual associations compared to the memory of unique objects based on their familiarity (Bartsch et al., 2010). Studies, like Stone SS’s. et al., In 2011, they show that an area of the hippocampus is activated during the presentation of space scenes or during the memorization of objects strongly related to specific places.
On the other hand, numerous clinical and subsequent investigations in animals, where the hippocampus was damaged, has concluded that this brain structure is necessary for the formation of declarative memories (Casanova et al., 2012). And that, in addition, the reduction in the ability to acquire new space memories is a process dependent on age (Nishimura et al., 2011). This suggests that there is a critical neuronal development period where their activity has consequences in the hippocampus and subsequent learning capabilities. Nishimura et al. (2011) state that, if the hippocampus develops normally, the basal dendrites of the CA1 hippocampus grow rapidly between postnatal days 6 and 25, but they cannot add additional branches or increase their length after this time. So dendritic growth can be key to proper learning.
Episodic memory decreases significantly with age, while semantic memory and implicit learning seem relatively stable throughout life (Nilsson, 2003; Rönlund et al., 2005). The decrease in episodic memory related to age also seems to have parallel deficits observed in patients with hippocampus damage, which mainly show a deteriorated associative memory function while the memory of a single element remains relatively intact (Konkel et al., 2008; Mayes et al., 2007, 2002; Turriziani et al., 2004); As memory for associations between items, or between items and its context, it repeatedly shows a greater decrease related to age compared to the memory for individual items material (Naveh-Beenjamin, 2000; Old and Naveh-Benjamin, 2008; Schacter et to the., 1991). Taken together, the findings point to the decrease related to age in episodic and spatial memory, largely driven by reduced associative and allocentric processes, as probably related to age -related alterations in the properties of the hippocampus.
In patients with amnesia and with injuries in the hippocampus and its subcortical connections, clear difficulties are seen in everything that implies the use of declarative memory (Giovanello et al., 2003), but instead, it seems that the ability to distinguish new objects recognizing others as relatives (Eichenbaum & Cohen, 2014) is intact. The comparison between objects that are familiar to the subject and those that are new seems to be associated with the hippocampus, as can be seen in the articles of Addis et al. (2004) and Bartsch et al., (2010). It has also been proven that when presenting space scenes or during the memorization tasks of objects related to specific places the parahipocampal cortex (Stone et al, 2011) is activated. The hippocampus seems to be, therefore, a key structure for the Information Association and its comparison based on the context and space in which such information is acquired.
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