Slide 4

Extracellular Recording of Repetitive Burst Discharges by Hubel and Wiesel

Hubel and Wiesel also noted that a subset of cortical neurons generated this unusual pattern of activity (repetitive burst firing at 30-70 Hz) in response to a visual stimulus.
This is Figure 5 from Hubel, D.H. and T.N. Wiesel (1965) Receptive fields and functional architecture in two nonstriate visual areas (18 and 19) of the cat. Journal of Neurophysiology 28: 229-289.