“We are very interested in how the positive (excitatory) and negative (inhibitory) inputs interact. We found something totally unexpected— inhibitory input is necessary for maintaining and sharpening orientation selectivity.”
In other words, without inhibitory synapses, an image’s edges and contours are blurred.
By Matthew Wiebe
Previous studies have shown that the arrangements of excitatory neuron circuits are sufficient for the brain to recognize shapes, but that conclusion is mostly based on output (nerve impulse) measurements only, says Tao, who looked at both output and input.
Tao and colleagues measured the nerve impulse as well as the excitatory and inhibitory currents that passed through individual cells in live mice as they were presented various visual stimuli.
They used a neuron model to determine how the inhibitory current affected the output response of the neuron and found that the ability to perceive orientation was most keen when both excitatory and inhibitory inputs were present and when the inhibitory input was strong.
“Inhibitory synapses weaken as people age,” Tao says. “This suggests that drugs that strengthen inhibitory activity may improve cognitive function among the elderly.”