A learning rule for place fields in a cortical model: theta phase precession as a network effect

We show that a model of the hippocampus introduced recently by Scarpetta, Zhaoping & Hertz ([2002] Neural Computation 14(10):2371-96), explains the theta phase precession phenomena. In our model, the theta phase precession comes out as a consequence of the associative-memory-like network dynamics, i.e. the network's ability to imprint and recall oscillatory patterns, coded both by phases and amplitudes of oscillation. The learning rule used to imprint the oscillatory states is a natural generalization of that used for static patterns in the Hopfield model, and is based on the spike time dependent synaptic plasticity (STDP), experimentally observed. In agreement with experimental findings, the place cell's activity appears at consistently earlier phases of subsequent cycles of the ongoing theta rhythm during a pass through the place field, while the oscillation amplitude of the place cell's firing rate increases as the animal approaches the center of the place field and decreases as the animal leaves the center. The total phase precession of the place cell is lower than 360 degrees, in agreement with experiments. As the animal enters a receptive field the place cell's activity comes slightly less than 180 degrees after the phase of maximal pyramidal cell population activity, in agreement with the findings of Skaggs et al (1996). Our model predicts that the theta phase is much better correlated with location than with time spent in the receptive field. Finally, in agreement with the recent experimental findings of Zugaro et al (2005), our model predicts that theta phase precession persists after transient intra-hippocampal perturbation.Comment: 10 pages, 7 figures, to be published in Hippocampu

Working memory dynamics and spontaneous activity in a flip-flop oscillations network model with a Milnor attractor

Many cognitive tasks require the ability to maintain and manipulate simultaneously several chunks of information. Numerous neurobiological observations have reported that this ability, known as the working memory, is associated with both a slow oscillation (leading to the up and down states) and the presence of the theta rhythm. Furthermore, during resting state, the spontaneous activity of the cortex exhibits exquisite spatiotemporal patterns sharing similar features with the ones observed during specific memory tasks. Here to enlighten neural implication of working memory under these complicated dynamics, we propose a phenomenological network model with biologically plausible neural dynamics and recurrent connections. Each unit embeds an internal oscillation at the theta rhythm which can be triggered during up-state of the membrane potential. As a result, the resting state of a single unit is no longer a classical fixed point attractor but rather the Milnor attractor, and multiple oscillations appear in the dynamics of a coupled system. In conclusion, the interplay between the up and down states and theta rhythm endows high potential in working memory operation associated with complexity in spontaneous activities

A Computational Predictor of Human Episodic Memory Based on a Theta Phase Precession Network

In the rodent hippocampus, a phase precession phenomena of place cell firing with the local field potential (LFP) theta is called “theta phase precession” and is considered to contribute to memory formation with spike time dependent plasticity (STDP). On the other hand, in the primate hippocampus, the existence of theta phase precession is unclear. Our computational studies have demonstrated that theta phase precession dynamics could contribute to primate–hippocampal dependent memory formation, such as object–place association memory. In this paper, we evaluate human theta phase precession by using a theory–experiment combined analysis. Human memory recall of object–place associations was analyzed by an individual hippocampal network simulated by theta phase precession dynamics of human eye movement and EEG data during memory encoding. It was found that the computational recall of the resultant network is significantly correlated with human memory recall performance, while other computational predictors without theta phase precession are not significantly correlated with subsequent memory recall. Moreover the correlation is larger than the correlation between human recall and traditional experimental predictors. These results indicate that theta phase precession dynamics are necessary for the better prediction of human recall performance with eye movement and EEG data. In this analysis, theta phase precession dynamics appear useful for the extraction of memory-dependent components from the spatio–temporal pattern of eye movement and EEG data as an associative network. Theta phase precession may be a common neural dynamic between rodents and humans for the formation of environmental memories

実験的・数理的アプローチに基づくヒト運動メカニズムに関する研究

国立大学法人長岡技術科学大

Hipokampální kódování pozic vizuálních objektů a predikce jejich budoucích interakcí

The hippocampus is a crucial brain structure involved in spatial navigation. It contains populations of spatially sensitive cells as the place cells, head-direction cells, grid cells, border cells, or object-vector cells. These neurons together create a cognitive map of the environment that serves for navigation in space. The role of hippocampal cells in the encoding of positions of other objects has also been suggested. Other studies found so-called time cells in the hippocampus that are active during specific delays in a behavioral task and associated them with place cells. While there are recent studies researching the encoding of accessible objects' positions, the encoding of objects in the inaccessible space has lacked research. The neural representation of dynamic situations (that constitute the majority of real-world encounters) has also been only scarcely researched. We designed a behavioral task to study the learning of static and dynamic spatial visual scenes presented in the inaccessible space and combined it with single-unit electrophysiological recording from the CA1 area of the hippocampus of freely moving rats. Our results show that rats can discriminate both static and dynamic inaccessible spatial stimuli, and that they prefer dynamic over static stimuli. They can also generalize...Hipokampus je klíčová oblast mozku účastnící se prostorové navigace. Obsahuje populace prostorově citlivých buněk jako jsou buňky místa, buňky směru hlavy, mřížkové buňky, hraniční buňky a "objektové vektorové" buňky. Tyto neurony společně tvoří kognitivní mapu prostředí, která slouží k orientaci v prostoru. Role hipokampálních buněk v kódování pozic okolních objektů byla také navržena. Další studie objevily v hipokampu takzvané buňky času, které jsou aktivní během specifických prodlev v behaviorální úloze, a asociovaly je s buňkami místa. Zatímco existují recentní studie zabývající se neurálním kódováním pozic přístupných objektů, kódování objektů v nepřístupném prostoru zatím nebylo příliš prozkoumáno. Neurální reprezentace dynamických situací (které představují většinu interakcí v reálném světě) je také prozkoumána jen řídce. Navrhli jsme behaviorální úlohu ke studiu učení statických a dynamických prostorových vizuálních scén prezentovaných v nepřístupném prostoru a zkombinovali ji s jednotkovým elektrofyziologickým nahráváním z CA1 oblasti hipokampu volně se pohybujících potkanů. Naše výsledky ukazují, že potkani dokáží diskriminovat statické i dynamické nepřístupné prostorové stimuly, a že preferují dynamické stimuly nad statickými. Také umí generalizovat nové dynamické stimuly na základě...Department of PhysiologyKatedra fyziologiePřírodovědecká fakultaFaculty of Scienc

Theta oscillations, timing and cholinergic modulation in the rodent hippocampal circuit

The medial temporal lobe (MTL) is crucial for episodic and spatial memory, and shows rhythmicity in the local field potential and neuronal spiking. Gamma oscillations (>40Hz) are mediatepd by local circuitry and interact with slower theta oscillations (6-10 Hz). Both oscillation frequencies are modulated by cholinergic input from the medial septum. Entorhinal grid cells fire when an animal visits particular locations in the environment arranged on the corners of tightly packed, equilateral triangles. Grid cells show phase precession, in which neurons fire at progressively earlier phases relative to theta oscillation as animals move through firing fields. This work focuses on the temporal organization of spiking and network rhythms, and their modulation by septal inputs, which are thought to be involved in MTL function. First, I recorded grid cells as rats explored open spaces and examined precession, previously only characterized on linear tracks, and compared it to predictions from models. I identified precession, including in conjunctive head-direction-by-grid cells and on passes that clipped the edge of the firing field. Secondly, I studied problems of measuring single neuron theta rhythmicity and developed an improved approach. Using the novel approach, I identified diverse modulation of rat medial entorhinal neurons’ rhythmic frequencies by running speed, independent from the modulation of firing rate by speed. Under pharmacological inactivation of the septum, rhythmic tuning was disrupted while rate tuning was enhanced. The approach also showed that available data is insufficient to prove that bat grid cells are arrhythmic due to low firing rates. In the final project, I optogenetically silenced cholinergic septal cells while recording from hippocampal area CA1. I identified changes in theta rhythmic currents and in theta-gamma coupling. This silencing disrupted performance when applied during the encoding phase of a delayed match to position task. These data support hypothetical roles of these rhythms in encoding and retrieval and suggest possible mechanisms for their modulation. Together, evidence from these projects suggests a role for theta in the function of spatial and episodic memory. These oscillations have important implications for communication and computation, and they can provide a substrate for efficient brain function