Neuroelectric Tuning of Cortical Oscillations by Apical Dendrites in Loop Circuits

Abstract

Bundles of relatively long apical dendrites dominate the neurons that make up the thickness of the cerebral cortex. It is proposed that a major function of the apical dendrite is to produce sustained oscillations at a specific frequency that can serve as a common timing unit for the processing of information in circuits connected to that apical dendrite. Many layer 5 and 6 pyramidal neurons are connected to thalamic neurons in loop circuits. A model of the apical dendrites of these pyramidal neurons has been used to simulate the electric activity of the apical dendrite. The results of that simulation demonstrated that subthreshold electric pulses in these apical dendrites can be tuned to specific frequencies and also can be fine-tuned to narrow bandwidths of less than one Hertz (1 Hz). Synchronous pulse outputs from the circuit loops containing apical dendrites can tune subthreshold membrane oscillations of neurons they contact. When the pulse outputs are finely tuned, they function as a local “clock,” which enables the contacted neurons to synchronously communicate with each other. Thus, a shared tuning frequency can select neurons for membership in a circuit. Unlike layer 6 apical dendrites, layer 5 apical dendrites can produce burst firing in many of their neurons, which increases the amplitude of signals in the neurons they contact. This difference in amplitude of signals serves as basis of selecting a sub-circuit for specialized processing (e.g., sustained attention) within the typically larger layer 6-based circuit. After examining the sustaining of oscillations in loop circuits and the processing of spikes in network circuits, we propose that cortical functioning can be globally viewed as two systems: a loop system and a network system. The loop system oscillations influence the network system’s timing and amplitude of pulse signals, both of which can select circuits that are momentarily dominant in cortical activity.

Apical amplification—a cellular mechanism of conscious perception?

“…These different proposals have different emphases, however. For example, whereas LaBerge and colleagues put emphasis on EEG rhythms and synchronized oscillations ( LaBerge and Kasevich 2017 ), we put emphasis on neuromodulatory arousal. These different emphases are mutually supportive, however, not antagonistic, because the different proposals share the common conception of apical dendrites in layer 1 as a channel for the amplification of selected signals.…”

Effectiveness of cathodal tDCS of the primary motor or sensory cortex in migraine: A randomized controlled trial

“…Allostatic loop system and network system oscillations influence dendritic or amplitude modulation (AM) and axonal or frequency modulation (FM) systems [14]. The excitatory alterations in these systems influence the reciprocal connectivity between receptorsynaptic potentials and action potentials [14,15]. Accordingly, informed by sensory-motor-network interactions and stress response domain interplayers, the electrophysiological homeostasis is altered abnormally (allostatic load) in a migraine brain [16,17].…”

Astrocytic modulation of cortical oscillations

“…More than a decade ago, Penttonen and Buzsáki postulated that at least ten distinct mechanisms are required to cover the large frequency range of cortical network oscillations 12 , 13 , and it has been reported that some frequency oscillations are driven by multiple mechanisms 14 . Several factors have been suggested to affect individual neuronal activity that underlie the generation of network oscillations, including the activation of intrinsic conductances by neuromodulators 6 , 13 , the influence of the dendritic structure 15 , activation of extrasynaptic receptors 16 , activation of astrocytic calcium activity 17 – 19 , cellular excitability 6 , 14 and the hyperpolarization-activated inward current I h , which can modulate membrane resonance in neurons 9 and is capable of regulating the strength and frequency of network oscillations 20 .…”