As is known, the visual scene is perceived stationary during active eye movements. An attempt to explain such a perceptual phenomenon has been that at the time of an active eye movement, the efferent motor discharge would be accompanied by a concurrent discharge into the central visual system, capable of counteracting those changes in retinal activation resulting from the ocular movement itself (corollary discharge theory). Only indirect psychophysic and electrophysiological data agree with such a hypothesis, whereas the only conclusive evidence would be to find a change in the activity of primary visual center neurons specifically related in time with an active displacement of the eye balls, without any stimulation of the retinal receptors, namely in dark adaptation. Bearing this in mind, experiments have been carried out in encéphale isolé dark adapted cats, where one may obtain a state of wakefulness accompanied by numerous, spontaneous eye movements, in order to ascertain whether active eye movements are time-locked with changes in central visual neuronal activity without any corresponding change in the output of the retinal ganglion cells. It was found: (1) transient increases in the neuronal firing of the central visual pathways (geniculo-cortical and corticofugal radiation) appeared related in time with active, bilateral and fast eye movements alone. (2) The increases in central visual impulse traffic were always bilateral and accompanied by the appearance of a distinctive wave pattern in the visual cortex. (3) No direct relationship could be shown between the amplitude and the duration of a transient enhancement in central visual activity and those of an eye movement. (4) The central visual phenomena always followed the oculomotor activation and were not dependent on peripheral inputs from the eyes. Although some characteristics of the observed changes in central visual firing time-locked with active eye movements may agree with the postulated corollary discharge, some others, such as the duration, intensity and timecourse, do not seem to conform with that theory, at least as it has been generally expressed.
Referenze Bibliografiche
[1] H. VON HELMHOLTZ, «Handbuch der physiologischen Optik», Voss, Leipzig (1867).
[2] E. VON HOLST e H. MITTELSTAEDT, «Naturwiss.», 37, 464 (1950).
[3] R. W. SPERRY, «J. Comp. Physiol. Psychol.», 43, 482 (1950).
[4] E. VON HOLST, «Brit. J. Animal Behaviour», 2, 89 (1954).
[5] H. L. TEUBER, Perception. In J. Field (Chief Ed.), «Handbook of Physiology», Sez. I, Vol. III, pp. 1595-1668, American Physiological Society, Washington, D.C. (1960).
[6] E. B. HOLT, «Harvard Psychol. Studies», 1, 3 (1903).
[7] R. W. DITCHBURN, «Optica Acta», 1, 171 (1955).
[8] P. S. LATOUR, «Vision Res.», 2, 261 (1962).
[9] B. L. ZUBER, L. STARK e M. LORBER, «Exptl. Neurol.», 14, 351 (1966).
[10] G. W. BEELER, «Vision Res.», 7, 769 (1967).
[11] E. G. GROSS, H. G. VAUGHAN e E. VALENSTEIN, «Electroenceph. clin. Neurophysiol.», 22, 204 (1967).
[12] J. A. MICHAEL e L. STARK, «Exptl. Neurol.», 17, 233 (1967).
[13] F. H. DUFFY e C. T. LOMBROSO, «Nature», 218, 1074 (1968).
[14] H. KAWAMURA e P. L. MARCHIAFAVA, «Arch. ital. Biol.», 106, 141 (1968).
[15] H. COLLEWIJN, «Vision Res.», 9, 803 (1969).
[16] K. MECHELSE, «J. Hirnforsch.», 5, 408 (1962).
[17] A. ARDUINI e G. RIZZOLATTI, «Boll. Soc. ital. Biol. sper.», 40, 885 (1964).
[18] A. ARDUINI e L. R. PINNEO, «Arch. ital. Biol.», 100, 415 (1962).
[19] F. MICHEL, A. RECHSTCHAFFEN e P. VIMONT, «C. R. Soc. Biol.», 158, 106 (1964).
[20] M. JOUVET, «Physiol. Rev.», 47, 117 (1967).
[21] S. COOPER e M. FILLENZ, «J. Physiol.», 127, 400 (1955).
[22] P. BACH-Y-RITA e K. MURATA, «Quart. J. Exptl. Physiol.», 49, 408 (1964).
[23] P. BACH-Y-RITA e F. ITO, «J. Physiol.», 186, 663 (1966).
Con il contributo del Ministero per i Beni e le Attività Culturali