Biomedical subjects

Anatoli Gorchetchnikov

Publications and source records attributed to Anatoli Gorchetchnikov.

4 recordsLinked to original sources

PubMed2007

Space, time and learning in the hippocampus: how fine spatial and temporal scales are expanded into population codes for behavioral control.

The hippocampus participates in multiple functions, including spatial navigation, adaptive timing and declarative (notably, episodic) memory. How does it carry out these particular functions? The present article proposes that hippocampal spatial and temporal processing are carried out by parallel circuits within entorhinal cortex, dentate gyrus and CA3 that are variations of the same circuit design. In particular, interactions between these brain regions transform fine spatial and temporal scales into population codes that are capable of representing the much larger spatial and temporal scales that are needed to control adaptive behaviors. Previous models of adaptively timed learning propose how a spectrum of cells tuned to brief but different delays are combined and modulated by learning to create a population code for controlling goal-oriented behaviors that span hundreds of milliseconds or even seconds. Here it is proposed how projections from entorhinal grid cells can undergo a similar learning process to create hippocampal place cells that can cover a space of many meters that are needed to control navigational behaviors. The suggested homology between spatial and temporal processing may clarify how spatial and temporal information may be integrated into an episodic memory. The model proposes how a path integration process activates a spatial map of grid cells. Path integration has a limited spatial capacity, and must be reset periodically, leading to the observed grid cell periodicity. Integration-to-map transformations have been proposed to exist in other brain systems. These include cortical mechanisms for numerical representation in the parietal cortex. As in the grid-to-place cell spatial expansion, the analog representation of number is extended by additional mechanisms to represent much larger numbers. The model also suggests how visual landmarks may influence grid cell activities via feedback projections from hippocampal place cells to the entorhinal cortex.

Animals↗

PubMedDate not supplied

A model of STDP based on spatially and temporally local information: derivation and combination with gated decay.

Temporal relationships between neuronal firing and plasticity have received significant attention in recent decades. Neurophysiological studies have shown the phenomenon of spike-timing-dependent plasticity (STDP). Various models were suggested to implement an STDP-like learning rule in artificial networks based on spiking neuronal representations. The rule presented here was developed under three constraints. First, it only depends on the information that is available at the synapse at the time of synaptic modification. Second, it naturally follows from neurophysiological and psychological research starting with Hebb's postulate [D. Hebb. (1949). The organization of behavior. Wiley, New York]. Third, it is simple, computationally cheap and its parameters are straightforward to determine. This rule is further extended by addition of four different types of gating derived from conventionally used types of gated decay in learning rules for continuous firing rate neural networks. The results show that the advantages of using these gatings are transferred to the new rule without sacrificing its dependency on spike-timing.

Algorithms↗

PubMedDate not supplied

Neuromodulation, theta rhythm and rat spatial navigation.

Cholinergic and GABAergic innervation of the hippocampus plays an important role in human memory function and rat spatial navigation. Drugs which block acetylcholine receptors or enhance GABA receptor activation cause striking impairments in the encoding of new information. Lesions of the cholinergic innervation of the hippocampus reduce the amplitude of hippocampal theta rhythm and cause impairments in spatial navigation tasks, including the Morris water maze, eight-arm radial maze, spatial reversal and delayed alternation. Here, we review previous work on the role of cholinergic modulation in memory function, and we present a new model of the hippocampus and entorhinal cortex describing the interaction of these regions for goal-directed spatial navigation in behavioral tasks. These mechanisms require separate functional phases for: (1) encoding of pathways without interference from retrieval, and (2) retrieval of pathways for guiding selection of the next movement. We present analysis exploring how phasic changes in physiological variables during hippocampal theta rhythm could provide these different phases and enhance spatial navigation function.

Animals↗

PubMedDate not supplied

Modeling goal-directed spatial navigation in the rat based on physiological data from the hippocampal formation.

We investigated the importance of hippocampal theta oscillations and the significance of phase differences of theta modulation in the cortical regions that are involved in goal-directed spatial navigation. Our models used representations of entorhinal cortex layer III (ECIII), hippocampus and prefrontal cortex (PFC) to guide movements of a virtual rat in a virtual environment. The model encoded representations of the environment through long-term potentiation of excitatory recurrent connections between sequentially spiking place cells in ECIII and CA3. This encoding required buffering of place cell activity, which was achieved by a short-term memory (STM) in EC that was regulated by theta modulation and allowed synchronized reactivation with encoding phases in ECIII and CA3. Inhibition at a specific theta phase deactivated the oldest item in the buffer when new input was presented to a full STM buffer. A 180 degrees phase difference separated retrieval and encoding in ECIII and CA3, which enabled us to simulate data on theta phase precession of place cells. Retrieval of known paths was elicited in ECIII by input at the retrieval phase from PFC working memory for goal location, requiring strict theta phase relationships with PFC. Known locations adjacent to the virtual rat were retrieved in CA3. Together, input from ECIII and CA3 activated predictive spiking in cells in CA1 for the next desired place on a shortest path to a goal. Consistent with data, place cell activity in CA1 and CA3 showed smaller place fields than in ECIII.

Action Potentials↗