In “encéphale isolé” cats, the electrical stimulation (15 to 300/sec) of one bulb induced in the contralateral one a negative shift of 0,2-0,5 millivolts. This effect disappears after section of the anterior commissure. Low frequency (8-10/sec) stimulation of the midline thalamic nuclei evokes in the bulb recruiting responses similar to those observed in the frontal cortex. The recruiting potentials are superimposed on a negative shift of 70 microvolts. High frequency activation of the same thalamic loci induces in the bulb a negative DC change of 150-200 microvolts. These effects disappear after cutting the olfactory peduncle. High frequency stimulation of the midbrain reticular formation yields a negative potential change of 100 microvolts in the bulbs, parallel to a generalized arousal. Similar effects are observed following electrical stimulation of the oral cavity or natural stimuli. The phenomena disappear after cutting the olfactory peduncle. This indicates that the olfactory bulb is centrifugally controlled by thalamic and reticular structures. Moreover a centrifugal control is exerted by one bulb on the contralateral one. Since one bulb has essentially inhibitory influence on the contralateral one, the hypothesis may be advanced that the DC negative shift recorded in the bulb is connected with inhibitory processes of underlying neurons.