PT  - JOURNAL ARTICLE
AU  - Carl E. Schoonover
AU  - Juan-Carlos Tapia
AU  - Verena C. Schilling
AU  - Verena Wimmer
AU  - Richard Blazeski
AU  - Wanying Zhang
AU  - Carol A. Mason
AU  - Randy M. Bruno
TI  - Comparative Strength and Dendritic Organization of Thalamocortical and Corticocortical Synapses onto Excitatory Layer 4 Neurons
AID  - 10.1523/JNEUROSCI.0305-14.2014
DP  - 2014 May 14
TA  - The Journal of Neuroscience
PG  - 6746--6758
VI  - 34
IP  - 20
4099  - http://www.jneurosci.org/content/34/20/6746.short
4100  - http://www.jneurosci.org/content/34/20/6746.full
SO  - J. Neurosci.2014 May 14; 34
AB  - Thalamus is a potent driver of cortical activity even though cortical synapses onto excitatory layer 4 neurons outnumber thalamic synapses 10 to 1. Previous in vitro studies have proposed that thalamocortical (TC) synapses are stronger than corticocortical (CC) synapses. Here, we investigated possible anatomical and physiological differences between these inputs in the rat in vivo. We developed a high-throughput light microscopy method, validated by electron microscopy, to completely map the locations of synapses across an entire dendritic tree. This demonstrated that TC synapses are slightly more proximal to the soma than CC synapses, but detailed compartmental modeling predicted that dendritic filtering does not appreciably favor one synaptic class over another. Measurements of synaptic strength in intact animals confirmed that both TC and CC synapses are weak and approximately equivalent. We conclude that thalamic effectiveness does not rely on enhanced TC strength, but rather on coincident activation of converging inputs.