Search

Spatial firing of hippocampal place cells varies depending on the animal's behavior relative to its goals. Here, rats were trained to approach visually guided reward ports in a two-dimensional open field. Hippocampal place cells encoded two independent pieces of information, spatial representation and goal-directed representation, by amplifying firing rates within their place fields specifically while the animal was moving toward a specific goal location. Irrespective of running speed and direction, substantial place-selective firing was observed that sustained a basal spatial map independent of goal-directed signals. When animals were allowed to freely forage in the field, in-field firing rates similarly increased when the animals transiently ran toward remembered goal locations. Disruption of medial septal activity significantly decreased goal-directed firing while maintaining spatial representation patterns. The findings indicate that the integrated encoding of spatial and goal-directed signals by hippocampal circuits is crucial for flexible spatial navigation to a goal location., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

Spike rates of a hippocampal place cell are not constant and vary even when an animal visits an identical place field with nearly identical behavior. As one potential neurophysiological source underlying place cell spiking variability, we focused on the temporally fluctuating activity states of neuronal ensembles. Spike patterns of hippocampal neurons were recorded from rats performing a linear track task. Within a single consummatory period, similar sets of neurons were more frequently recruited in synchronous firing events, whereas different synchronized firing patterns of neuronal populations tended to be identified in different consummatory periods. A linear regression analysis indicated that the time-varying activation patterns of neuronal populations during consummatory periods are correlated with the spike rates of a place cell within its place field during running. These findings suggest that place cell in-field spiking is not only triggered by static inputs that represent external environments but also strongly depends on the time-varying internal states of neuronal populations., (© 2018 Wiley Periodicals, Inc.)

The hippocampal formation located in the medial temporal lobe of the brain has been studied extensively for several decades, both in in vitro slice preparations and in vivo living animals. Recent advancements in large-scale recording techniques, such as multisite silicon probes and tetrodes, enable us to examine the detailed characteristics of temporal spiking patterns of tens or hundreds of neurons in the hippocampal circuit. Here, we introduce how such tools contribute to our understanding of the hippocampal network dynamics and review several hippocampal functions for information processing in the brain, including pattern separation and completion, spatial representation, and encoding of positive and negative valence.

Acute alcohol exposure impairs hippocampus-dependent spatial memory. However, there is little evidence for the effects of ethanol on the spike patterns of hippocampal cell populations. Here, we examined how the spatial firing patterns of place cells, neurons that encode specific locations, were altered in rats that were intraperitoneally injected with 1.5 g/kg ethanol. Ethanol administration partly reduced or abolished place-selective spiking of a subset of place cells during running periods in a spatial task, whereas a subset of place fields newly emerged, suggesting a partial reorganization of hippocampal spatial maps by ethanol. On the other hand, ethanol administration did not significantly alter the frequency of hippocampal sharp-wave ripple (SWRs) and synchronous spike patterns during resting periods, suggesting that offline memory consolidation and retrieval mechanisms underpinned by hippocampal neuronal synchronization are not strongly affected by ethanol. These results indicate that acute ethanol intake mainly affects the encoding of external information but has little impact on internal memory processing. [ABSTRACT FROM AUTHOR]