Cognitive demands induce selective hippocampal reorganization: Arc expression in a place and response task

Abstract

Place cells in the hippocampus can maintain multiple representations of a single environment and respond to physical and/or trajectory changes by remapping. Within the hippocampus there are anatomical, electrophysiological, and behavioral dissociations between the dorsal and ventral hippocampus and within dorsal CA1. Arc expression was used to measure the recruitment of ensembles across different hippocampal subregions in rats trained to utilize two different cognitive strategies while traversing an identical trajectory. This behavioral paradigm allowed for the measurement of remapping in the absence of changes in external cues, trajectory traversed (future/past), running speed, motivation, or different stages of learning. Changes in task demands induced remapping in only some hippocampal regions: reorganization of cell ensembles was observed in dorsal CA1 but not in dorsal CA3. Moreover, a gradient was found in the degree of remapping within dorsal CA1 that corresponds to entorhinal connectivity to this region. Remapping was not seen in the ventral hippocampus: neither ventral CA1 nor CA3 exhibited ensemble changes with different cognitive demands. This contrasts with findings of remapping in both the dorsal and ventral dentate gyrus using this task. The results suggest that the dorsal pole of the hippocampus is more sensitive to changes in task demands.

Theta Dynamics in Rat: Speed and Acceleration across the Septotemporal Axis

“…The findings of the current research highlight the importance of controlling for locomotor indices when attempting to relate theta indices to cognitive operations [12], [40]–[41], particularly in experimental paradigms that involve manipulations (e.g., behavioral choices, pharmacologic), sensorimotor variables and correlated changes in theta spectral indices. The present findings demonstrate predictable changes in theta LFP signals in relation to acceleration and deceleration and how that relationship changes along the septotemporal axis of the HPC.…”

“…The increase in theta power as a function of running speed has been confirmed in subsequent studies [37]–[39], but recently has been shown to vary systematically across the long axis of the HPC [28], [30]. Most rodent studies examining the relationship between cognitive performance and theta involve spatial locomotion often along relatively fixed trajectories [12], [40]–[41] and can involve deceleration when animals are within regions of “choice” (often turns). Thus, a better understanding of the relative contribution of speed and acceleration to changes in theta should facilitate our understanding of how variations in theta relate to sensorimotor and/or cognitive processes.…”

Transcription of the Immediate-Early GeneArcin CA1 of the Hippocampus Reveals Activity Differences along the Proximodistal Axis That Are Attenuated by Advanced Age

“…These results are also interesting to consider with respect to the findings of Schmidt et al (2012). The authors visualized Arc expression to compare population activity between distal and proximal CA1 while rats found reward in a radial arm maze using two different cognitive strategies.…”

Adult Hippocampal Neurogenesis, Fear Generalization, and Stress

“…However, global remapping in the DG is not just observed during discrimination of contextual representations, instead resolving conflicting goals also engenders global remapping in the DG (Satvat et al, 2011;Schmidt et al, 2012b). Thus, pattern separation in the DG-CA3 circuit may constrain the overgeneralization of fear in ambiguous threatening contexts or when threat is uncertain.…”