Discussion of jsiegle's comment: Using a 10 x 10 array of electrodes in cat or monkey visual cortex, the authors measured traveling waves in the LFP. Spontaneously arising waves propagated radially at a speed of 0.25 m/s (monkeys) or 0.3 m/s (cats). Similar waves could be evoked by visual stimulation. Both the distance and magnitude of these evoked waves was dependent on stimulus contrast. At 25% contrast, waves had a space constant of ~1.3 mm (vs. almost 2 mm for spontaneous waves) and a the magnitude went down by 1/5. At 100% contrast, waves had a space constant of ~0.8 mm, and magnitude was reduced by 1/4. Thus, stronger stimuli still elicit traveling waves, but they are lower in amplitude and more focal. This result is an example how functional connectivity in the cortex can be altered in a stimulus-specific manner.