Numerous studies have shown that neuronal re- sponses are modulated by stimulus properties and also by the state of the local network. However, little is known about how activity fluctuations of neuronal populations modulate the sensory tuning of cells and affect their encoded information. We found that fluc- tuations in ongoing and stimulus-evoked population activity in primate visual cortex modulate the tuning of neurons in a multiplicative and additive manner. While distributed on a continuum, neurons with stronger multiplicative effects tended to have less additive modulation and vice versa. The information encoded by multiplicatively modulated neurons increased with greater population activity, while that of additively modulated neurons decreased. These effects offset each other so that population ac- tivity had little effect on total information. Our results thus suggest that intrinsic activity fluctuations may act as a ‘‘traffic light’’ that determines which subset of neurons is most informative.

I.A.-R. is supported by a PhD grant from the Department of Education, Linguistic Politics, and Culture of the Basque Government. A.K. is supported by the NIH (EY016774), an Irma T. Hirschl Career Scientist Award, and Research to Prevent Blindness. R.M.-B. is supported by the Ramon y Cajal Spanish Award RYC-2010-05952, the Marie Curie FP7-PEOPLE-2010-IRG grant PIRG08-GA-2010-276795, and the Spanish PSI2013-44811-P grant. I.A.-R.