A Double Dissociation between Hippocampal Subfields

Abstract

Computational theories have suggested different functions for the hippocampal subfields (e.g., CA1 and CA3) in memory. However, it has been difficult to find dissociations relevant to these hypothesized functions in investigations of the hippocampal correlates of space ("place fields") in freely behaving animals. The current study demonstrates a double dissociation between the shifts in the center of mass (COM) of the place fields that were simultaneously recorded in CA1 and CA3 when familiar cue configurations were dynamically changed over days. The COM of CA3 place fields shifted backward in the first experience of the cue-changed environment, whereas the COM of CA1 place fields did not display the backward shift until the next day. These results support the hypothesis that CA3 plays a key role in the rapid formation of representations of new spatiotemporal sequences, whereas CA1 may be more important for comparing currently experienced sequence information with stored sequences in the CA3 network.

Slow and Fast Gamma Rhythms Coordinate Different Spatial Coding Modes in Hippocampal Place Cells

“…The center of mass for fast gamma-associated place fields was shifted 0.3 ± 5.5 cm after the overall place field center (fast gamma center of mass after slow gamma center of mass: t(368) = 1.9, p = 0.05; Figures 3 and S3). The backward shift observed during slow gamma is reminiscent of the backward shift that CA1 place fields develop within the first few track laps each day (Mehta et al, 1997; Mehta et al, 2000; Lee et al, 2004). Consistent with this earlier research, few prospective coding events were observed during the first minute on the track each day (Figure 4A).…”

“…These prospective and retrospective coding modes are believed to reflect distinct memory processing states in the entorhinal-hippocampal network. Prospective coding is reminiscent of the backward expansion of CA1 place fields that develops with experience (Mehta et al, 1997; Mehta et al, 2000; Lee et al, 2004). Development of such expansion is blocked by NMDA receptor antagonists (Ekstrom et al, 2001), which also block spatial learning (Morris et al, 1986).…”

Neural Population Evidence of Functional Heterogeneity along the CA3 Transverse Axis: Pattern Completion versus Pattern Separation

“…CA2 representational plasticity has been studied with IEG expression (Wintzer et al, 2014), and interesting differences with CA3 have been reported. It will be important for future studies to concentrate on this long-neglected component of the hippocampal pyramidal layer to understand its precise computational roles in comparison with the differentiated roles of CA3 and CA1 that have begun to be unraveled in the past decade (Guzowski et al, 2004; Lee et al, 2004a; Lee et al, 2004b; Leutgeb et al, 2004). …”

Attentive scanning behavior drives one-trial potentiation of hippocampal place fields

“…Several decades of place field studies have shown that, in a familiar environment under familiar behavioral conditions, place fields in rats are mostly stable 31 , with only subtle changes such as the size or shape of place fields 27,32,33 or population-level representations that can change gradually as a function of time or experience 34–37 . The long-term stability in familiar environments 31 raised the question of how the system is able to encode the items and events of experience to form an episodic memory in a stable environment.…”