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bioRxiv · 10.1101/034918

Transition between functional regimes in an integrate-and-fire network model of the thalamus

Alessandro Barardi·Jordi Garcia-Ojalvo·Alberto Mazzoni
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Abstract

The thalamus is a key brain element in the processing of sensory information. During the sleep and awake states, this brain area is characterized by the presence of two distinct dynamical regimes: in the sleep state activity is dominated by spindle oscillations (7 - 15 Hz) weakly affected by external stimuli, while in the awake state the activity is primarily driven by external stimuli. Here we develop a simple and computationally efficient model of the thalamus that exhibits two dynamical regimes with different information-processing capabilities, and study the transition between them. The network model includes glutamatergic thalamocortical (TC) relay neurons and gabaergic reticular (RE) neurons described by adaptative integrate-and-fire models in which spikes are induced by either depolarization or hyperpolarization rebound. We found a range of connectivity conditions under which the thalamic network composed by these neurons displays the two aforementioned dynamical regimes. Our results show that TC-RE loops generate spindle-like oscillations and that a critical value of clustering in the RE-RE connections is necessary for the coexistence of the two regimes. We also observe that the transition between the two regimes occurs when the external excitatory input on TC neurons (mimicking sensory stimulation) is large enough to cause a significant fraction of them to switch from hyperpolarization-rebound-driven firing to depolarization-driven firing. Overall, our model gives a novel and clear description of the role that the two types of neurons and their connectivity play in the dynamical regimes observed in the thalamus, and in the transition between them. These results pave the way for the development of efficient models of the transmission of sensory information from periphery to cortex.\n\nAuthor SummaryThe thalamus is known to exhibit two clearly distinct dynamical regimes with different functionalities. During slow-wave sleep the thalamus is dominated by internal activity and is hardly sensitive to external stimuli. In contrast, in the awake state, the thalamus modulates its activity according to the stimuli coming from the periphery. Here we study the conditions regulating the transition between these two states. To that end we implement a simple yet biologically realistic neuronal network model of the thalamus, based on single-neuron models that reproduce the properties of the two prominent types of thalamic neurons, namely thalamocortical relay cells and reticular neurons. We found that when reticular neurons are clustered the network exhibits two distinct dynamical regimes; one dominated by oscillations and insensitive to external stimuli (like sleep) and one sensitive to them (like wake). Moreover we found that the transition between the two regimes is due to the increase of the external excitatory input (corresponding to stronger sensory stimuli).

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Alessandro Barardi, Jordi Garcia-Ojalvo, Alberto Mazzoni. 2015-12-20. Transition between functional regimes in an integrate-and-fire network model of the thalamus. https://doi.org/10.1101/034918

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