Using dual intracellular recordings it was previously shown that the membrane potential of nearby cortical cells in the visual cortex of anesthetized cats is highly synchronized. Similar behavior is found in the barrel cortex of the rat. We utilize this technique to investigate the real-time relation between excitation and inhibition during ongoing activity and during sensory evoked response. Our recently obtained data indicate that the excitatory network is under continuous control of inhibition.
State dependent balance of excitation and inhibition
The prominent feedback connections between excitatory and inhibitory neurons in the mammalian cortex suggest that the cortex may operate at a balanced state in which inhibition modulates the magnitude of excitation. We recorded intracellularly the ongoing excitatory and inhibitory inputs onto cortical neurons across distinct brain states, induced by altering the depth of anesthesia. While the magnitude of inhibition increased under the deeper-state, the magnitude of excitation was not state-dependent. Importantly, because these results were recapitulated using different anesthetics, we propose that state-dependent changes in the balance between excitation and inhibition are mediated upstream to the cortex. That excitation was indifferent to the state-dependent changes in inhibition, suggests that ongoing cortical activity is not at a balanced state but rather operates as expected from feedforward mechanisms.
Spatial integration, the process by which different elements of an object that activates a neuron are summed, is fundamental to all sensory modalities. We have found that summation is sublinear and usually the size of the evoked synaptic potential when two whiskers are stimulated simultaneously is almost equal to the larger of the two individual responses.