Brief periods of fast oscillatory potentials (100-600 Hz) have been described in the neocortex and hippocampus of mammals, spontaneously (Chrobak & Buzsaki, 1996; Grenier et al. 2001) or during electrical (Kandel & Buzsaki, 1997) and natural sensory stimulation (Jones & Barth, 1999). In particular, fast oscillations are prominent components of the somatic evoked potential recorded in the somatosensory cortex of anesthetized and awake animals, including humans (sigma bursts) (Curio et al. 1997). Although fast oscillatory activity is becoming a subject attracting increasing interest, its mechanisms and functional, or pathological role remain to be determined. Here we report that visual stimulation elicits robust traveling waves of fast oscillatory activity in the optic tectum (OT) of awake and anaesthetized pigeons. The avian OT is a complex multilayered sensorial structure that is considered operationally analogous to the mammalian sensory cortex. Adult pigeons were anaesthetized with a mixture of Ketamine (40 mg/kg) and Xylazine (12 mg/kg) injected intramusculary in the pectoral muscles and supplemented by 13 mg/kg ketamine and 4 mg/kg every 2 hours. The body temperature was maintained at 39-41°C by a DC-powered blanket. The heart rate was continously monitored and local wounds and pressure points were treated with anaesthesic ointment. A craneotomy exposing the dorso-lateral tectum was performed and tungsten microelectrodes were then lowered into the tectum under visual guidance. Visually triggered tectal fast oscillations consist of trains of 3-12 short (2-6 msec), very large (400 microvolts), high frequency (600 Hz) bursts, separated by 25 ms, corresponding to a 42 Hz gamma frequency. Due to their high amplitude and fast dynamics, these oscillations may have been confused previously with regular multi-unitary potentials. Tectal fast oscillations have three main characteristics also found in stimulus evoked fast oscillations in mammalian somatosensory cortex. First, they are always superimposed on the rising phase of a slower evoked field negative potential. Second, they are generated locally by radially oriented dipoles. And third, focal visual stimulation elicites traveling waves of fast oscillations that propagated laterally for distances up to 1 mm from the stimulated site. These results demonstrate that sensory evoked waves of fast oscillations are not particular to the mammalian cortex. Notwithstanding the differences in neural architecture, the remarkable similarities we found between tectal and cortical phenomenology suggest that these waves of fast oscillations may represent the action of a neural mechanism that plays a key role in the operation of sensorial laminar structures. We suggest this role is related to a local attentional mechanism that modulates surrounding neural circuits prior to the arrival of the sensory stimulus.