Abstract
L5 pyramidal neurons are the only neocortical cell type with dendrites reaching all six layers of cortex, casting them as one of the main integrators in the cortical column. What is the nature and mode of computation performed in mouse primary visual cortex (V1) given the physiology of L5 pyramidal neurons? First, we experimentally establish active properties of the dendrites of L5 pyramidal neurons of mouse V1 using patch-clamp recordings. Using a detailed multi-compartmental model, we show this physiological setup to be well suited for coincidence detection between basal and apical tuft inputs by controlling the frequency of spike output. We further show how direct inhibition of calcium channels in the dendrites modulates such coincidence detection. To establish the singe-cell computation that this biophysics supports, we show that the combination of frequency-modulation of somatic output by tuft input and (simulated) calcium-channel blockage functionally acts as a composite sigmoidal function. Finally, we explore how this computation provides a mechanism whereby dendritic spiking contributes to orientation tuning in pyramidal neurons.
Highlights
Layer 5 (L5) of neocortex contains excitatory pyramidal neurons considered a main integration unit of the cortical column that project to other areas of neocortex as well as subcortical structures
We perform patch clamp recordings in the apical dendrites to establish the spatial distribution of nonlinear channels and the signals they support in the dendrites of layer 5 pyramidal neurons of the mouse primary visual cortex
We summarize the results of the simulations using a simple abstracted model, that describes the computation layer 5 pyramidal neurons perform on synaptic input
Summary
Layer 5 (L5) of neocortex contains excitatory pyramidal neurons considered a main integration unit of the cortical column that project to other areas of neocortex as well as subcortical structures. The properties of L5 pyramidal neuron dendrites have been extensively studied in vitro, with the vast majority of the electrophysiological work performed in hippocampus [2], somatosensory [3] and prefrontal cortex [4,5] of rats This line of research has shown that pyramidal neurons in different cortical regions contain voltage-gated Na+ channels along the dendritic trunk which support the backpropagation of action potentials (APs) from the soma into dendrites [6], as well as voltage-gated Ca2+ channels that support spiking in the apical dendrite [3,7]. Neurons from higher order visual areas, such as the latero-medial area of mouse visual cortex, project axons to the upper layers of the primary visual cortex [11,12] Alongside these long-range axons, reciprocal excitatory connections exist [1]. We find that mouse L5 pyramidal neurons in V1 support backpropagating action potentials (bAPs), and dendritic Ca2+ spiking
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