Network models of frequency modulated sweep detection. Skorheim S, Razak K, Bazhenov M. PLoS One. 2014 Dec 16;9(12):e115196.

Frequency modulated (FM) sweeps are common in species-specific vocalizations, including human speech. Auditory neurons selective for the direction and rate of frequency change in FM sweeps are present across species, but the synaptic mechanisms underlying such selectivity are only beginning to be understood. Even less is known about mechanisms of experience-dependent changes in FM sweep selectivity. We present three network models of synaptic mechanisms of FM sweep direction and rate selectivity that explains experimental data: (1) The ‘facilitation’ model contains ...

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The impact of cortical deafferentation on the neocortical slow oscillation. Lemieux M, Chen JY, Lonjers P, Bazhenov M, Timofeev I. J Neurosci. 2014 Apr 16;34(16):5689-703.

Slow oscillation is the main brain rhythm observed during deep sleep in mammals. Although several studies have demonstrated its neocortical origin, the extent of the thalamic contribution is still a matter of discussion. Using electrophysiological recordings in vivo on cats and computational modeling, we found that the local thalamic inactivation or the complete isolation of the neocortical slabs maintained within the brain dramatically reduced the expression of slow and fast oscillations in affected cortical areas. ...

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Synchronization of isolated downstates (K-complexes) may be caused by cortically-induced disruption of thalamic spindling. Mak-McCully RA, Deiss SR, Rosen BQ, Jung KY, Sejnowski TJ, Bastuji H, Rey M, Cash SS, Bazhenov M, Halgren E. PLoS Comput Biol. 2014 Sep 25;10(9):e1003855. doi: 10.1371/journal.pcbi.1003855.

Sleep spindles and K-complexes (KCs) define stage 2 NREM sleep (N2) in humans. We recently showed that KCs are isolated downstates characterized by widespread cortical silence. We demonstrate here that KCs can be quasi-synchronous across scalp EEG and across much of the cortex using electrocorticography (ECOG) and localized transcortical recordings (bipolar SEEG). We examine the mechanism of synchronous KC production by creating the first conductance based thalamocortical network model of N2 sleep to generate both spontaneous spindles and KCs. Spontaneous ...

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Top-Down Inputs Enhance Orientation Selectivity in Neurons of the Primary Visual Cortex during Perceptual Learning. Moldakarimov S, Bazhenov M, Sejnowski TJ. PLoS Comput Biol. 2014 Aug 14.

Perceptual learning has been used to probe the mechanisms of cortical plasticity in the adult brain. Feedback projections are ubiquitous in the cortex, but little is known about their role in cortical plasticity. Here we explore the hypothesis that learning visual orientation discrimination involves learning-dependent plasticity of top-down feedback inputs from higher cortical areas, serving a different function from plasticity due to changes in recurrent connections within a cortical area. In a Hodgkin-Huxley-based spiking neural network model of visual cortex, ...

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The impact of cortical deafferentation on the neocortical slow oscillation. Lemieux M, Chen J-Y, Lonjers P, Bazhenov M, Timofeev I. Journal of Neuroscience, April, 2014

During natural slow-wave sleep (SWS), brain activity recorded from electroencephalogram (EEG) is characterized by large-amplitude fluctuations of field potential, which reflect synchronous alternating periods of activity (cortical Up states) and silence (cortical Down states) across the thalamocortical system. Recovery of slow oscillations after extensive thalamic lesions and the absence of slow oscillations in the thalamus of decorticated cats pointed to an intracortical origin for this rhythm. If was suggested that thalamic neurons play a merely secondary role simply ...

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Heterosynaptic Plasticity: Multiple Mechanisms and Multiple Roles. Chistiakova M1, Bannon NM, Bazhenov M, Volgushev M. Neuroscientist. 2014 Apr 11.

Plasticity is a universal property of synapses. It is expressed in a variety of forms mediated by a multitude of mechanisms. Here we consider two broad kinds of plasticity that differ in their requirement for presynaptic activity during the induction. Homosynaptic plasticity occurs at synapses that were active during the induction. It is also called input specific or associative, and it is governed by Hebbian-type learning rules. Heterosynaptic plasticity can be induced by episodes of strong postsynaptic activity also at ...

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Congratulations to Oscar Gonzales for receiving NSF pre-doctoral award

The National Science Foundation’s Graduate Research Fellowship Program GRFP recognizes and supports outstanding graduate students in NSF-supported science, technology, engineering, and mathematics disciplines who are pursuing research-based master’s and doctoral degrees at accredited US institutions.  Oscar Gonzales was awarded by this prestigious fellowship for his research on the topic of epileptogenesis and seizures.

 

Breaking in precise balance of excitation and inhibition in brain networks may promote hyper-synchronization and lead to epileptic seizures. Multiple factors potentially affecting this delicate balance include ...

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A Spiking Network Model of Decision Making Employing Rewarded STDP. Skorheim S, Lonjers P, Bazhenov M. PLoS One. 2014 Mar 14;9(3):e90821.

Rewarded spike timing dependent plasticity (STDP) has been implicated as a possible learning mechanism in a variety of brain systems. This mechanism combines unsupervised STDP that modifies synaptic strength depending on the relative timing of presynaptic input and postsynaptic spikes together with a reinforcement signal that modulates synaptic changes. In this study, rewarded STDP was implemented as part of a spiking network model of excitatory cells and inhibitory interneurons. The network was used to model basic foraging behavior ...

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Our research on sleep spindles analysis is awarded by grant from the National Institute on Aging

Sleep facilitates the consolidation of memories. The number of sleep spindles (transient neural events in non rapid eye movement (NREM) sleep, 9–15 Hz) in a post-training sleep period correlates with the magnitude of declarative memory improvement (e.g., conscious, episodic memories), whereas minutes in REM sleep correlate with improvement in non-declarative memories (e.g., unconscious, perceptual or sensorimotor skills).

Although the studies report that individual sleep features correlate with improvement in specific memory domains, we do not know if manipulating these sleep features ...

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