Only about 5% of the inputs onto brain cells (neurons) in visual cortex are from the eye. The rest of the inputs, 95%, come from other parts of the brain. Nevertheless, cortical neurons respond vigorously to visual stimuli.

The recent paper “Synchrony of Thalamocortical Inputs Maximizes Cortical Reliability” published April 2, 2010 in Science asks if the relative times of arrival among signals at synapses on a cortical neuron influence its chance of responding to a visual stimulus.

The research team simulated a cortical neuron known as a layer 4 spiny stellate cell with 5,800 synaptic inputs. Three hundred of the synapses on the simulated cell received thalamic input patterns previously recorded from live animals presented with drifting grating patterns of light. (The thalamus gets input from retinal ganglion cells found in the eyeball.) The other 5,500 synapses consisted of excitatory and inhibitory input from other cortical areas.

The number of thalamocortical synapses simultaneously driven by the visual stimulus was measured and compared with the simulated neuron’s response. They found that the reliability of transmitting the signal from thalamus to the cortical neuron increased steeply when between 20 and 40 synapses were active within the same 5 millisecond time window. The result is striking when you consider that it’s only 20 to 40 synapses out of 5,800!


Other related blog posts:

Correlated Response Fluctuations Between Cortical Neurons Rare

A Question of Synchrony, Correlation or Active Decorrelation among Brain Cell Responses