Dendritic and Axonal Propagation Delays May Shape Neuronal Networks With Plastic Synapses

Abstract

Biological neuronal networks are highly adaptive and plastic. For instance, spike-timing-dependent plasticity (STDP) is a core mechanism which adapts the synaptic strengths based on the relative timing of pre- and postsynaptic spikes. In various fields of physiology, time delays cause a plethora of biologically relevant dynamical phenomena. However, time delays increase the complexity of model systems together with the computational and theoretical analysis burden. Accordingly, in computational neuronal network studies propagation delays were often neglected. As a downside, a classic STDP rule in oscillatory neurons without propagation delays is unable to give rise to bidirectional synaptic couplings, i.e., loops or uncoupled states. This is at variance with basic experimental results. In this mini review, we focus on recent theoretical studies focusing on how things change in the presence of propagation delays. Realistic propagation delays may lead to the emergence of neuronal activity and synaptic connectivity patterns, which cannot be captured by classic STDP models. In fact, propagation delays determine the inventory of attractor states and shape their basins of attractions. The results reviewed here enable to overcome fundamental discrepancies between theory and experiments. Furthermore, these findings are relevant for the development of therapeutic brain stimulation techniques aiming at shifting the diseased brain to more favorable attractor states.

Myelinated axon physiology and regulation of neural circuit function

“…Also, the tuning of synaptic strength through long-term plasticity (potentiation or depression) is highly dependent upon the temporal interval and the order of spiking activity of both presynaptic and postsynaptic synapses (spike-time dependent plasticity, STDP) and is central to models of circuit-level plasticity, development, and learning (Feldman, 2012). Myelinated axon output may be ideally suited to generate STDP in some circuits, and recent computational modeling indicates that physiological axonal spike propagation delays have the potential to yield novel neuronal activity and synaptic connectivity patterns, which cannot be captured by classic STDP models (Asl, Valizadeh, & Tass, 2018). Despite the fact that the nature of AP arrival (regulated entirely by the myelinated axon) influence presynaptic function, the role that regulation of any component of the myelinated axon, or the output of the entire unit plays in synapse function has been hugely understudied and represents a major challenge for the field.…”

Anchoring Groups Determine Conductance, Thermopower and Thermoelectric Figure of Merit of an Organic Molecular Junction

“…In this context, the long-term memory in the device conductance can be manipulated by successive application of appropriate electrical pulses; a counterpart of the spike-timing-dependent plasticity in the brain that modifies the synaptic strengths between neurons [67,68]. At higher levels, these memory devices can be integrated in crossbar arrays [69] representing the strength of plastic synaptic connections in brain neural networks [70,71]. The results presented here may contribute to further understanding of how the conductance of such molecular structures could be modified/controlled by the modification of anchoring groups or side groups.…”

Synchronization in Networks With Heterogeneous Adaptation Rules and Applications to Distance-Dependent Synaptic Plasticity

“…The main difference of system Eqs. 1, 2 from the models considered previously in the literature [40,70,71,74,82], is that the plasticity functions h ij can be different for each network connection j → i.…”