Geon Memory Engram Cells and Spiny Neurons Memory

 

A memory does not reside in a small brain area. Rather, it is represented by a large population of neurons distributed over the brain (Herry and Johansen, 2014). Several lines of evidence suggest that memory could be stored in spiny neurons (Figure 7-1).

  1. Spiny neurons are characterized by a large number of dendritic branches and spines, well-suited for the storage of memory.
  2. More than 90% of granule cells in the dentate gyrus are silent, which may result from memory extinction.
  3. The neurons in neocortex layer 5, basolateral amygdala, and striatum exhibit slow oscillations (Neske, 2016; Crane et al., 2009; Frederick et al., 2014), which have been demonstrated to orchestrate memory consolidation during sleep (Mölle and Born, 2011).
Image

Figure 7-1. Examples of spiny neurons. The upper image is a camera lucida drawing, while the lower image is a conceptual representation of the dendritic tree. The granule cells of the dentate gyrus (not shown) may also be considered as spiny neurons. [Source: Oikonomou et al., 2014]

Not all spiny neurons are involved in memory storage. For instance, the stellate cells of entorhinal cortex are unlikely to be the memory engram cells because they are highly excitable (Alonso and Klink, 1993). The engram cells should be prone to silence, encoding the extinction state of memories.

While memories are stored in distributed brain areas (Herry and Johansen, 2014), experiments have demonstrated that stimulation of the dentate gyrus is sufficient to retrieve particular fear memories (Liu et al., 2012), even for amnesic memory that cannot be retrieved by natural reminding cues (Ryan et al., 2015; Roy et al., 2017).

 

Author: Frank Lee
First Published: January, 2018