The Excitatory Neuronal Network of the C2 Barrel Column in Mouse Primary Somatosensory Cortex

Abstract

Local microcircuits within neocortical columns form key determinants of sensory processing. Here, we investigate the excitatory synaptic neuronal network of an anatomically defined cortical column, the C2 barrel column of mouse primary somatosensory cortex. This cortical column is known to process tactile information related to the C2 whisker. Through multiple simultaneous whole-cell recordings, we quantify connectivity maps between individual excitatory neurons located across all cortical layers of the C2 barrel column. Synaptic connectivity depended strongly upon somatic laminar location of both presynaptic and postsynaptic neurons, providing definitive evidence for layer-specific signaling pathways. The strongest excitatory influence upon the cortical column was provided by presynaptic layer 4 neurons. In all layers we found rare large-amplitude synaptic connections, which are likely to contribute strongly to reliable information processing. Our data set provides the first functional description of the excitatory synaptic wiring diagram of a physiologically relevant and anatomically well-defined cortical column at single-cell resolution.

Sensory experience modifies spontaneous state dynamics in a large-scale barrel cortical model

“…However, Song et al (2005) reported that the probability of connection does not depend systematically on the distance in the same neuronal type in the visual cortex. In support of the latter, Lefort et al (2009) found no significant drop in connectivity over the distances explored in a single mouse barrel. As a result, there is not sufficient evidence to suggest a significant decrease in connection probability with distance within the same barrel and, consequently, we have not incorporated such dependence in our model.…”

“…Our (Lefort et al 2009)). The proportion of excitatory to inhibitory neurons in layers II/III is approximately 9:1.…”

“…The values used for the neuronal connectivity probabilities are listed in Table 2. Where available, the table entries were taken from the literature and as above, the entries with asterisks denote values taken from Lefort et al (2009).…”

“…Specifically, Holmgren et al (2003) Izhikevich & Edelman (2008). The entries with asterisks are taken from Lefort et al (2009 reported a decrease from 9% probability of two cells within ± 25 µm of each other being connected, to 1% at distances > 100 µm for p II/III -p II/III synapses in visual and somatosensory cortex. However, Song et al (2005) reported that the probability of connection does not depend systematically on the distance in the same neuronal type in the visual cortex.…”

“…The model is based on the physiological literature (e.g. Lefort et al 2009), including both the numbers and proportions of neurons of each class, their connectivity probabilities and delays. Model parameters are tuned to achieve essential physiological features such as firing rates and stationarity.…”