Central mechanisms counteract visually induced tonus asymmetries
- 22 Downloads
Body and ocular postural responses of restrained and freely swimming normal, bilaterally labyrinthectomized, and unilaterally blindfolded goldfish to different angles of illumination were determined by single-frame analysis of videotapes.
In restrained normal animals ocular deviation to illumination from one side did not reach values high enough to compensate completely for the angle of incident light. The magnitude of ocular deviation elicited was even smaller than the degree of body roll induced under identical light conditions in freely swimming specimens. Similar findings were obtained with somewhat larger ocular and body responses in bilaterally labyrinthectomized and in unilaterally blindfolded fish.
Ocular responses to passive tilt were stronger than to unilateral illumination, but did not fully compensate for the applied tilt. Illumination from the dorsal side while the animals were passively tilted reduced ocular displacements.
Ocular responses of restrained animals to illumination from above and below were qualitatively identical.
In restrained animals eyes deviated in response to unilateral illumination drifted back towards their normal position in the orbit when bilaterally symmetrical light conditions were provided. The ocular drift curve had an exponential shape. Bilaterally labyrinthectomized specimens needed longer periods of time to re-assume the ocular zero position than normal fish did. This difference appears to be due to higher starting values of ocular deviations in labyrinthectomized animals, as time constants of drifts were found to be around 20 s in both types of experimental subjects.
Our data are interpreted as demonstrating the existence of CNS mechanisms counteracting sense-organ induced central tonus asymmetries.
dorsal light response
Unable to display preview. Download preview PDF.