Memory  >   Memory Consolidation: Sharp Wave Ripples Provide Glutamate

Sharp wave ripples (SWRs) refer to a wave pattern in the electroencephalography (EEG) that oscillate at the frequency between 110 Hz and 200 Hz. They are generated in the hippocampal CA3 and then rapidly propagate to CA1, possibly through gap junctions (Draguhn et al., 1998; Spruston, 2001). CA3 contains a recurrent circuit (Figure 32-1) that can generate SWRs spontaneously (Buzsáki, 2015). SWRs may occur in the awake state reflecting "hippocampal replay" of previous experiences. They are also present in slow wave sleep, responsible for the dialogue between the hippocampus and cortex. SWRs have been demonstrated to play a crucial role in memory consolidation (Rothschild et al., 2017).


Figure 32-1. The microcircuit formed by the dentate gyrus (DG), CA3 and entorhinal cortex layer II (EC2). [Source: Prince et al., 2016]

Generation of SWRs in the CA3-CA1 regions may send glutamatergic inputs to other regions in the memory engram network, particularly mPFC, DG, amygdala and nucleus accumbens (located in the striatum). The build-up of glutamate pond can then produce NMDA plateaus and activate the memory units encoding a specific memory (Chapter 9). In the awake state, this may lead to retrieval of the memory. During slow wave sleep, the subject cannot experience the memory as consciousness is lost. However, in both cases, the Ca2+ ions accompanied with the NMDA plateau may trigger synaptogenesis to strengthen the memory.


Author: Frank Lee
First published: July, 2018