scholarly journals Reconciling contrast invariance and non-linear computation in cortical circuits

2021 ◽  
Author(s):  
L. Bernáez Timón ◽  
P. Ekelmans ◽  
S. Konrad ◽  
A. Nold ◽  
T. Tchumatchenko
Keyword(s):  
Synaptic Plasticity ◽  
Piriform Cortex ◽  
Mean Field ◽  
Dependent Manner ◽  
Cortical Circuits ◽  
Stimulus Contrast ◽  
Spiking Network ◽  
Network Simulations ◽  
Contrast Invariance ◽  
Balanced Networks

AbstractNetwork selectivity for orientation is invariant to changes in the stimulus contrast in the primary visual cortex. Similarly, the selectivity for odor identity is invariant to changes in odorant concentration in the piriform cortex. Interestingly, invariant network selectivity appears robust to local changes in synaptic strength induced by synaptic plasticity, even though: i) synaptic plasticity can potentiate or depress connections between neurons in a feature-dependent manner, and ii) in networks with balanced excitation and inhibition, synaptic plasticity is a determinant for the network non-linearity. In this study, we investigate whether network contrast invariance is consistent with a variety of synaptic states and connectivities in balanced networks. By using mean-field models and spiking network simulations, we show how the synaptic state controls the non-linearity in the network response to contrast and how it can lead to the emergence of contrast-invariant or contrast-dependent selectivity. Different forms of synaptic plasticity sharpen or broaden the network selectivity, while others do not affect it. Our results explain how the physiology of individual synapses is linked to contrast-invariant selectivity at the network level.

scholarly journals Sparse balance: excitatory-inhibitory networks with small bias currents and broadly distributed synaptic weights

2021 ◽  
Author(s):  
Ramin Khajeh ◽  
Francesco Fumarola ◽  
LF Abbott
Keyword(s):  
Mean Field ◽  
Field Analysis ◽  
Cortical Circuits ◽  
Recurrent Excitation ◽  
Nonlinear Responses ◽  
Gaussian Statistics ◽  
Non Gaussian ◽  
Sparse Set ◽  
Balanced Networks ◽  
Inhibitory Networks

Cortical circuits generate excitatory currents that must be cancelled by strong inhibition to assure stability. The resulting excitatory-inhibitory (E-I) balance can generate spontaneous irregular activity but, in standard balanced E-I models, this requires that an extremely strong feedforward bias current be included along with the recurrent excitation and inhibition. The absence of experimental evidence for such large bias currents inspired us to examine an alternative regime that exhibits asynchronous activity without requiring unrealistically large feedforward input. In these networks, irregular spontaneous activity is supported by a continually changing sparse set of neurons. To support this activity, synaptic strengths must be drawn from high-variance distributions. Unlike standard balanced networks, these sparse balance networks exhibit robust nonlinear responses to uniform inputs and non-Gaussian statistics. In addition to simulations, we present a mean-field analysis to illustrate the properties of these networks.

scholarly journals Imbalanced amplification: A mechanism of amplification and suppression from local imbalance of excitation and inhibition in cortical circuits

2017 ◽  
Author(s):  
Christopher Ebsch ◽  
Robert Rosenbaum
Keyword(s):  
Field Theory ◽  
Mean Field Theory ◽  
Mean Field ◽  
Cortical Circuits ◽  
Response Properties ◽  
Biologically Relevant ◽  
Linear Correction ◽  
External Stimuli ◽  
The Relationship ◽  
Balanced Networks

AbstractUnderstanding the relationship between external stimuli and the spiking activity of cortical populations is a central problem in neuroscience. Dense recurrent connectivity in local cortical circuits can lead to counterintuitive response properties, raising the question of whether there are simple arithmetical rules for relating circuits’ connectivity structure to their response properties. One such arithmetic is provided by the mean field theory of balanced networks, which is derived in a limit where excitatory and inhibitory synaptic currents precisely balance on average. However, balanced network theory is not applicable to some biologically relevant connectivity structures. We show that cortical circuits with such structure are susceptible to an amplification mechanism arising when excitatory-inhibitory balance is broken at the level of local subpopulations, but maintained at a global level. This amplification, which can be quantified by a linear correction to the classical mean field theory of balanced networks, explains several response properties observed in cortical recordings.

scholarly journals All-Trans Retinoic Acid induces synaptic plasticity in human cortical neurons

2020 ◽  
Author(s):  
Maximilian Lenz ◽  
Pia Kruse ◽  
Amelie Eichler ◽  
Julia Muellerleile ◽  
Jakob Straehle ◽  
...  
Keyword(s):  
Retinoic Acid ◽  
Synaptic Plasticity ◽  
Cortical Neurons ◽  
Mrna Translation ◽  
Dependent Manner ◽  
Human Cortex ◽  
Functional Changes ◽  
Trans Retinoic Acid ◽  
All Trans Retinoic Acid ◽  
Structural And Functional Properties

ABSTRACTA defining feature of the brain is its ability to adapt structural and functional properties of synaptic contacts in an experience-dependent manner. In the human cortex direct experimental evidence for synaptic plasticity is currently missing. Here, we probed plasticity in human cortical slices using the vitamin A derivative all-trans retinoic acid, which has been suggested as medication for the treatment of neuropsychiatric disorders, e.g., Alzheimer’s disease. Our experiments demonstrate coordinated structural and functional changes of excitatory synapses of superficial (layer 2/3) pyramidal neurons in the presence of all-trans retinoic acid. This synaptic adaptation is accompanied by ultrastructural remodeling of the calcium-storing spine apparatus organelle and requires mRNA-translation. We conclude that all-trans retinoic acid is a potent mediator of synaptic plasticity in the adult human cortex.

scholarly journals Emergence of Functional Specificity in Balanced Networks with Synaptic Plasticity

2015 ◽  
Vol 11 (6) ◽  
pp. e1004307 ◽  
Author(s):  
Sadra Sadeh ◽  
Claudia Clopath ◽  
Stefan Rotter
Keyword(s):  
Synaptic Plasticity ◽  
Functional Specificity ◽  
Balanced Networks

scholarly journals Recurrent cortical circuits implement concentration-invariant odor coding

Science ◽  
2018 ◽  
Vol 361 (6407) ◽  
pp. eaat6904 ◽  
Author(s):  
Kevin A. Bolding ◽  
Kevin M. Franks
Keyword(s):  
Olfactory Bulb ◽  
Concentration Dependence ◽  
Neural Circuit ◽  
Feedback Inhibition ◽  
Piriform Cortex ◽  
Cortical Activity ◽  
Cortical Circuits ◽  
Odor Coding ◽  
Recurrent Collateral ◽  
The Impact

Animals rely on olfaction to find food, attract mates, and avoid predators. To support these behaviors, they must be able to identify odors across different odorant concentrations. The neural circuit operations that implement this concentration invariance remain unclear. We found that despite concentration-dependence in the olfactory bulb (OB), representations of odor identity were preserved downstream, in the piriform cortex (PCx). The OB cells responding earliest after inhalation drove robust responses in sparse subsets of PCx neurons. Recurrent collateral connections broadcast their activation across the PCx, recruiting global feedback inhibition that rapidly truncated and suppressed cortical activity for the remainder of the sniff, discounting the impact of slower, concentration-dependent OB inputs. Eliminating recurrent collateral output amplified PCx odor responses rendered the cortex steeply concentration-dependent and abolished concentration-invariant identity decoding.

scholarly journals Synaptic control of DNA methylation involves activity-dependent degradation of DNMT3A1 in the nucleus

2020 ◽  
Vol 45 (12) ◽  
pp. 2120-2130 ◽  
Author(s):  
Gonca Bayraktar ◽  
PingAn Yuanxiang ◽  
Alessandro D. Confettura ◽  
Guilherme M. Gomes ◽  
Syed A. Raza ◽  
...  
Keyword(s):  
Dna Methylation ◽  
Synaptic Plasticity ◽  
Promoter Methylation ◽  
Dna Methyltransferase ◽  
De Novo ◽  
Memory Formation ◽  
Epigenetic Mark ◽  
Dependent Manner ◽  
Synaptic Control ◽  
Activity Dependent

Abstract DNA methylation is a crucial epigenetic mark for activity-dependent gene expression in neurons. Very little is known about how synaptic signals impact promoter methylation in neuronal nuclei. In this study we show that protein levels of the principal de novo DNA-methyltransferase in neurons, DNMT3A1, are tightly controlled by activation of N-methyl-D-aspartate receptors (NMDAR) containing the GluN2A subunit. Interestingly, synaptic NMDARs drive degradation of the methyltransferase in a neddylation-dependent manner. Inhibition of neddylation, the conjugation of the small ubiquitin-like protein NEDD8 to lysine residues, interrupts degradation of DNMT3A1. This results in deficits in promoter methylation of activity-dependent genes, as well as synaptic plasticity and memory formation. In turn, the underlying molecular pathway is triggered by the induction of synaptic plasticity and in response to object location learning. Collectively, the data show that plasticity-relevant signals from GluN2A-containing NMDARs control activity-dependent DNA-methylation involved in memory formation.

Sevoflurane Blocks Cholinergic Synaptic Transmission Postsynaptically but Does Not Affect Short-term Potentiation

2005 ◽  
Vol 102 (5) ◽  
pp. 920-928 ◽  
Author(s):  
Hiroaki Naruo ◽  
Shin Onizuka ◽  
David Prince ◽  
Mayumi Takasaki ◽  
Naweed I. Syed
Keyword(s):  
Synaptic Plasticity ◽  
Synaptic Transmission ◽  
Fluorescent Imaging ◽  
Posttetanic Potentiation ◽  
Dependent Manner ◽  
General Anesthetics ◽  
Short Term ◽  
Concentration Dependent Manner ◽  
Cholinergic Synaptic Transmission ◽  
Term Potentiation

Background As compared with their effects on both inhibitory and excitatory synapses, little is known about the mechanisms by which general anesthetics affect synaptic plasticity that forms the basis for learning and memory at the cellular level. To test whether clinically relevant concentrations of sevoflurane affect short-term potentiation involving cholinergic synaptic transmission, the soma-soma synapses between identified, postsynaptic neurons were used. Methods Uniquely identifiable neurons visceral dorsal 4 (presynaptic) and left pedal dorsal 1 (postsynaptic) of the mollusk Lymnaea stagnalis were isolated from the intact ganglion and paired overnight in a soma-soma configuration. Simultaneous intracellular recordings coupled with fluorescent imaging of the FM1-43 dye were made in either the absence or the presence of sevoflurane. Results Cholinergic synapses, similar to those observed in vivo, developed between the neurons, and the synaptic transmission exhibited classic short-term, posttetanic potentiation. Action potential-induced (visceral dorsal 4), 1:1 excitatory postsynaptic potentials were reversibly and significantly suppressed by sevoflurane in a concentration-dependent manner. Fluorescent imaging with the dye FM1-43 revealed that sevoflurane did not affect presynaptic exocytosis or endocytosis; instead, postsynaptic nicotinic acetylcholine receptors were blocked in a concentration-dependent manner. To test the hypothesis that sevoflurane affects short-term potentiation, a posttetanic potentiation paradigm was used, and synaptic transmission was examined in either the presence or the absence of sevoflurane. Although 1.5% sevoflurane significantly reduced synaptic transmission between the paired cells, it did not affect the formation or retention of posttetanic potentiation at this synapse. Conclusions This study demonstrates that sevoflurane blocks cholinergic synaptic transmission postsynaptically but does not affect short-term synaptic plasticity at the visceral dorsal 4-left pedal dorsal 1 synapse.

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