Mice preferentially use increases in cerebral cortex spike rates to detect changes in visual stimuli

When the retinal image changes, some neurons in primary visual cortex (V1) increase their rate of spiking, while other decrease their rate of spiking. How the brain decodes changes in visual stimuli from this set of neuronal responses remains largely unknown. We trained mice to respond to increases or decreases of visual contrast by releasing a lever. We used optogenetic approaches to increase or decrease V1 neuron responses evoked by contrast changes. The ability of mice to detect increases and decreases in visual contrast were both enhanced by increasing V1 spiking, whereas detection was always impaired by suppressing V1 spiking, even when the change was a decrease in contrast. The results suggest a strong asymmetry in the readout of signals from V1 insomuch as decrements in neuronal spiking contribute markedly less to perceptual reports.