Forward Dendritic Spikes: A Mechanism for Parallel Processing in Dendritic Subunits and Shifting Output Codes

Forward Dendritic Spikes: A Mechanism for Parallel Processing in Dendritic Subunits and Shifting Output Codes

Oscar Herreras (Cajal Institute, Spain), Julia Makarova (Cajal Institute, Spain) and José Manuel Ibarz (Hospital Ramón y Cajal, Spain)
DOI: 10.4018/978-1-59904-996-0.ch003

Abstract

Neurons send trains of action potentials to communicate each other. Different messages are issued according to varying inputs, but they can also mix them up in a multiplexed language transmitted through a single cable, the axon. This remarkable property arises from the capability of dendritic domains to work semi autonomously and even decide output. We review the underlying mechanisms and theoretical implications of the role of voltage-dependent dendritic currents on the forward transmission of synaptic inputs, with special emphasis in the initiation, integration and forward conduction of dendritic spikes. When these spikes reach the axon, output decision was made in one of many parallel dendritic substations. When failed, they still serve as an internal language to transfer information between dendritic domains. This notion brakes with the classic view of neurons as the elementary units of the brain and attributes them computational/storage capabilities earlier billed to complex brain circuits.
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Channels In Dendrites: A Conceptual Revolution

Based on modeling studies, some authors, suggested that the overall firing pattern is somehow engraved in the architecture of the dendritic tree (Mainen et al., 1995). Indeed, some architectonic dendritic prototypes have been preserved in specific brain nuclei spanning long periods of brain evolution. Although this may be indicative of a common integrative function being preserved to carry out a specific task, the large number of exceptions clearly argue against this hypothesis. Certainly, the physical structure of the dendritic arbors has a notable influence in the processing of inputs, and even some computational capabilities arise from it (see Segev and London, 1999). Nevertheless, most dendrites are active neuron elements, not mere passive cables. The number and variety of ion channels in their membranes modulate synaptic currents with a strength and complexity largely overcoming that of the cable structure. These “modulatory” dendritic currents have the same voltage-dependent nature as those in the soma and axon, and have been called intrinsic currents to differentiate them from the synaptic currents that co-activate and co-localize with them.

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