Memory, navigation and theta rhythm in the hippocampal-entorhinal system

Abstract

Theories on the functions of the hippocampal system are based largely on two fundamental discoveries: the amnestic consequences of removing the hippocampus and associated structures in the famous patient H.M. and the observation that spiking activity of hippocampal neurons is associated with the spatial position of the rat. In the footsteps of these discoveries, many attempts were made to reconcile these seemingly disparate functions. Here we propose that mechanisms of memory and planning have evolved from mechanisms of navigation in the physical world and hypothesize that the neuronal algorithms underlying navigation in real and mental space are fundamentally the same. We review experimental data in support of this hypothesis and discuss how specific firing patterns and oscillatory dynamics in the entorhinal cortex and hippocampus can support both navigation and memory.

Slow-theta power decreases during item-place encoding predict spatial accuracy of subsequent context recall

“…Part of these effects was apparent in the hippocampal entorhinal complex, a core system for memory and spatial navigation and functionally linked to theta oscillations (Buzsáki and Moser, 2013). Acknowledging the importance of this system for the successful performance of our study's task, by extension, it is plausible that slow theta negative SMEs manifested in actively engaged brain regions.…”

“…Applying this contrast to electrophysiological activity has additionally revealed that SMEs are associated with specific frequency bands, helping to delineate how encoding processes are regulated by oscillatory activity. Among these frequencies, the 4 8 Hz band received special attention in humans because it resembles the theta rhythm of small mammals, which has ex tensively shown memory related properties (Buzsáki and Moser, 2013;Hasselmo, 2005). For example, in rabbits, hippocampal theta activity pre dicts the learning rate of classical conditioning, whereas its loss impairs spatial memory in rats (Winson, 1978).…”

How Animals Find Their Way in Space. Experiments and Modeling

“…Различные исследователи фиксируют такие функции гиппокампа, как хранение рабочей памяти, формирование и воспроизведение долговременной памяти, детекция новизны стимулов, формирование сложных условных рефлексов, интеграция сигналов разной модальности, ориентация в пространстве. Непонятно, каким образом сравнительно небольшая и довольно простая по своей организации структура может участвовать в столь разных видах деятельности (некоторые соображения о совмещении гиппокампом функций памяти и ориентации можно найти в [27,28]). …”

“…На сегодняшний день общепризнано, что система клеток решетки выполняет функцию интегрирования пути, в этом вопросе согласны как ведущие экспериментаторы в этой области, такие как Бужаки и Мозер [27], так и авторы ведущих модельных работ [63][64][65]. Эти представления лежат в основе всех предложенных моделей, объясняющих механизм преобразования информации о скорости и направлении движения животного в активность животного.…”

Planning of spatially-oriented locomotion following focal brain damage in humans: A pilot study

“…Answers to these questions have come mainly from animal studies where different types of cells in the rat hippocampus and in neighboring regions (e.g., para-hippocampus and entorhinal cortex) were found to signal various spatial attributes [see Ref. [1] for a recent review]. These include the position of the animal in the room (the so-called "place cells"), its spatial orientation ("head direction cells") and, the metrics or the boundaries of the surrounding space ("grid" and "border" cells, respectively).…”