Quantitative measurements of centrally and retinally generated saccadic suppression in a locust movement detector neurone.

1. Chronic recordings from tethered but otherwise freely moving locusts demonstrate that the response of the descending contralateral movement detector (d.c.m.d.) neurone, an identified visual interneurone of the brain, is greatly reduced during the performance of saccades. 2. The reduction in the response of the d.c.m.d. is effected by both a centrally generated corollary discharge and the changing contrast of the image of the visual background on the retina. 3. The corollary discharge that is concomitant with a saccade reduces the d.c.m.d. response by 0 . 94 log units, and this reduction is independent of contrast frequency. 4. Changing contrast produced by relative motion of eye and background reduces the sensitivity of the d.c.m.d. neurone by 0 . 16 log units for each 10-fold increase in contrast frequency. This retinally generated reduction in sensitivity is not significantly different whether the locust performs saccades or is fixating with the visual background passively moved. The maximal reduction in the d.c.m.d. response by retinal sources is 0 . 45 log units. 5. Proprioceptive reafference does not contribute significantly to saccadic suppression of the response of the d.c.m.d. neurone.