Exploring the role of context‐dependent hippocampal activity in spatial alternation behavior

Abstract

In a continuous T-maze spatial alternation task, CA1 place cells fire differentially on the stem of the maze as rats are performing left- and right-turn trials (Wood et al. (2000) Neuron 27:623-633). This context-dependent hippocampal activity provides a potential mechanism by which animals could solve the alternation task, as it provides a cue that could prime the appropriate goal choice. The aim of this study was to examine the relationship between context-dependent hippocampal activity and spatial alternation behavior. We report that rats with complete lesions of the hippocampus learn and perform the spatial alternation task as well as controls if there is no delay between trials, suggesting that the observed context-dependent hippocampal activity does not mediate alternation behavior in this task. However lesioned rats are significantly impaired when delays of 2 or 10 s are interposed. Recording experiments reveal that context-dependent hippocampal activity occurs in both the delay and no-delay versions of the task, but that in the delay version it occurs during the delay period, and not on the stem of the maze. These data are consistent with a role for context-dependent hippocampal activity in delayed spatial alternation, but suggest that, according to specific task demands and memory load, the activity may be generated by different mechanisms and/or in different brain structures.

Gamma oscillations dynamically couple hippocampal CA3 and CA1 regions during memory task performance

“…2A) (24). This task requires rats to encode their spatial response on each trial and, after a 10-second delay, retrieve this information to appropriately choose the opposite arm from the one entered on the previous trial.…”

“…For example, synchronization of neuronal activity into coherent gamma-frequency oscillations can serve to bind representations (20,21) and couple hippocampal and rhinal cortices during successful formation of declarative memories (22). To examine how regional networks within the hippocampal formation are dynamically coordinated during the retrieval process, we recorded LFPs from rats with high-density silicon probe arrays (23) during performance of a hippocampusdependent delayed spatial alternation task on a modified T maze (24). Because gamma oscillations in the hippocampus show clear regional and laminar patterns and the CA3 region is known to generate self-organized gamma oscillatory patterns (25)(26)(27)(28), we examined the laminar-specific power and coherence of gamma oscillations.…”

Ventral Midline Thalamus Is Critical for Hippocampal-Prefrontal Synchrony and Spatial Working Memory

“…Many studies have linked the dorsal hippocampus with SWM in rodents (Dudchenko et al, 2000;Ainge et al, 2007;Czerniawski et al, 2009;Hallock et al, 2013a), making it a prime candidate for the provision of SWM-specific information to the mPFC. The results of the current study are consistent with research that has shown SWM-specific functional synchronization between the dorsal hippocampus and mPFC (Jones and Wilson, 2005;Hyman et al, 2010;Sigurdsson et al, 2010;O'Neill et al, 2013) and further implicates different patterns of hippocampal-prefrontal oscillatory synchrony during SWM-guided behavior.…”

“…Rats in Experiment 2 were given an infusion (0.5 l volume) of a fluorophore-conjugated muscimol (BODIPY TMR-X; Life Technologies) 30 min before perfusion (Allen et al, 2008). To visualize placement of the internal cannulae for rats in Experiment 2, half of the brain slices from Re/Rh were stained using cresyl violet.…”

“…Lesions of the rodent dorsal hippocampus (Dudchenko et al, 2000;Ainge et al, 2007;Czerniawski et al, 2009;Hallock et al, 2013a), but not the ventral hippocampus (Czerniawski et al, 2009), disrupt SWM and the rodent mPFC functionally synchronizes with the dorsal hippocampus during successful performance of SWM tasks (Jones and Wilson, 2005;Hyman et al, 2010;Sigurdsson et al, 2010;O'Neill et al, 2013), supporting the conclusion that the rodent dorsal hippocampus is critical for SWM-guided decision making. Despite evidence that dorsal hippocampal-mPFC interactions are both correlated with (Jones and Wilson, 2005;Hyman et al, 2010;Sigurdsson et al, 2010) and necessary for (Lee and Kesner, 2003) SWM in rodents, the rodent mPFC receives direct inputs only from the ventral hippocampus (Swanson, 1981;Ferino et al, 1987;Jay et al, 1989;Thierry et al, 2000).…”