Effect of head tilt on visual cortical cell function in the intact and labyrinthectomized cat

The area of the receptive field, its length and width, its position in the visual field, the peristimulus time (PST) histogram (i.e., the response to successive moving light-bar stimuli), the directional preference, the velocity gradient, and the intertrial (spontaneous) firing rate were studied electrophysiologically in complex cortical visual cells in Brodmann's area 18. These characteristics were explored after head tilt, in immobilized cats, both in intact and in bilaterally labyrinthectomized animals. In intact animals (in 64 cells), most of these characteristics changed after head tilts of 10, 20, 30, or 40 degrees to the right or to the left of the horizontal plane. There was always one specific head position in which the receptive field area was at its smallest. In labyrinthectomized animals (in 29 cells), the lengths, widths, and the areas of the receptive fields were only minimally altered during identical tilts. Similarly, in the labyrinthectomized cats, head tilts (40 degrees, to the right or left) caused no substantial changes in the shape and duration of the PST histogram, compared with those in intact cats. No two visual cortical cells responded to head tilts in exactly the same manner. Such uniqueness in response is probably of importance during visual image analysis; in particular, as it relates to cortical reconstruction of stable visual images during continuously changing head movements and positions.