  Numerous studies have shown that neuronal responses 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
fluctuations 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 activity 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 are most informative.
