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. 2014 Feb 18:8:75.
doi: 10.3389/fnhum.2014.00075. eCollection 2014.

The spectro-contextual encoding and retrieval theory of episodic memory

Andrew J Watrous  1 , Arne D Ekstrom  2
Affiliations

The spectro-contextual encoding and retrieval theory of episodic memory

Andrew J Watrous et al. Front Hum Neurosci. .

Abstract

The spectral fingerprint hypothesis, which posits that different frequencies of oscillations underlie different cognitive operations, provides one account for how interactions between brain regions support perceptual and attentive processes (Siegel etal., 2012). Here, we explore and extend this idea to the domain of human episodic memory encoding and retrieval. Incorporating findings from the synaptic to cognitive levels of organization, we argue that spectrally precise cross-frequency coupling and phase-synchronization promote the formation of hippocampal-neocortical cell assemblies that form the basis for episodic memory. We suggest that both cell assembly firing patterns as well as the global pattern of brain oscillatory activity within hippocampal-neocortical networks represents the contents of a particular memory. Drawing upon the ideas of context reinstatement and multiple trace theory, we argue that memory retrieval is driven by internal and/or external factors which recreate these frequency-specific oscillatory patterns which occur during episodic encoding. These ideas are synthesized into a novel model of episodic memory (the spectro-contextual encoding and retrieval theory, or "SCERT") that provides several testable predictions for future research.

Keywords: cell assembly; context reinstatement; cross-frequency coupling; episodic memory; hippocampus; neocortex; oscillations; phase-synchronization.

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Figures

FIGURE 1
FIGURE 1
Levels of organization in neural systems and the associated findings at each level relevant for SCERT.
FIGURE 2
FIGURE 2
Schematic depiction of SCERT. In this scenario, a person perceives (via active sensing) and encodes a woman (green) who introduces herself as Ann (red) on the corner of first street (blue). Associated activity in different brain areas is shown for each type of information in a different color; stimulus representations are shown in prototypical brain areas for clarity but may also be more diffusely distributed throughout the brain. Phase-locking of neuronal ensembles for each region is shown for the initial representation and following learning. Episodic encoding is associated with phase synchronization between areas and CFC between assemblies representing different aspects of the experience. During retrieval, a partial cue (encountering first street) initially drives hippocampal activity to reinstate the spectral signature associated with the encoding experience. Note that some aspects of SCERT, including neuronal resonance and frequency multiplexing, are not depicted.
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