Pyramidal cell communication within local networks in layer 2/3 of rat neocortex

Abstract

The extent to which neocortical pyramidal cells function as a local network is determined by the strength and probability of their connections. By mapping connections between pyramidal cells we show here that in a local network of about 600 pyramidal cells located within a cylindrical volume of 200 microm x 200 microm of neocortical layer 2/3, an individual pyramidal cell receives synaptic inputs from about 30 other pyramidal neurons, with the majority of EPSP amplitudes in the 0.2-1.0 mV range. The probability of connection decreased from 0.09 to 0.01 with intercell distance (over the range 25-200 microm). Within the same volume, local interneuron (fast-spiking non-accommodating interneuron, FS)-pyramidal cell connections were about 10 times more numerous, with the majority of connections being reciprocal. The probability of excitatory and inhibitory connections between pyramidal cells and FS interneurons decreased only slightly with distance, being in the range 0.5-0.75. Pyramidal cells in the local network received strong synaptic input during stimulation of afferent fibres in layers 1 and 6. Minimal-like stimulation of layer 1 or layer 6 inputs simultaneously induced postsynaptic potentials in connected pyramidal cells as well as in pyramidal-FS cell pairs. These inputs readily induced firing of pyramidal cells, although synaptically connected cells displayed different firing patterns. Unitary EPSPs in pyramidal-pyramidal cell pairs did not detectably alter cell firing. FS interneurons fire simultaneously with pyramidal cells. In pyramidal-FS cell pairs, both unitary EPSPs and IPSPs efficiently modulated cell firing patterns. We suggest that computation in the local network may proceed not only by direct pyramidal-pyramidal cell communication but also via local interneurons. With such a high degree of connectivity with surrounding pyramidal cells, local interneurons are ideally poised to both coordinate and expand the local pyramidal cell network via pyramidal-interneuron-pyramidal communication.

Specific excitatory connectivity for feature integration in mouse primary visual cortex

“…In our models, each neuron had a Gaussian dendritic field of ρ d = 75 μm (corresponding to an approximate width of 4ρ = 300 μm; [59]); and axonal field of ρ a,e = 290 μm for excitatory neurons (width 1100 μm; [59][60][61]) and ρ a,i = 100 μm for inhibitory neurons (width 400 μm; [62]). Table 2.…”

Pyramidal and Granule Cells Distribution through Hippocampal Fields: An Index for Sensory Information Processing

“…The balance of excitatory and inhibitory synapses is crucial for that propagation [45]. Indeed, in vivo experiments showed that computation proceeds by direct pyramidal-pyramidal cell communication in the neocortex [46] and assemblies may transiently form [47]. Firing rate modulations are transmitted linearly through many layers in neocortex [48].…”

The Neuronal Network Oscillation as a Critical Phenomenon

“…The connectivity probability for excitatory and inhibitory neurons was varied independently and is defined as the percentage of neurons that a neuron connects to within its local range. In neocortical tissue, local functional connectivity between neurons decays with distance; however, only a few empirical reports have assessed this quantitatively [62,63]. Given the small radius of connectivity, this was implemented as an exponential decay.…”