The electrical responses of the thalamic pulvinar (of its analogue, the nucleus lateralis posterior (nLP)) to light stimuli of various intensity were recorded in awake rabbits, and their interrelationships with the responses of the retina, superior colliculi, and visual cortex were analyzed. It is postulated that a major role in the afferent supply of the rabbit nLP belongs to the optic track and the superior colliculi. The presence was demonstrated of a highly organized analyzer of the reticular control of nLP function that is of a facilitatory character. The most important role in reticular influence belongs to its adrenoresponsive mechanism. An inhibitory influence was demonstrated for the visual and sensorimotor regions of the cerebral cortex on the nLP neuronal apparatus producing responses to light stimuli. The influence of the visual cortex are the most pronounced and stable.
It has been demonstrated in chronic experiments on awake rabbits that a solitary stimulation of the middle hypothalamus, its ventromedial and lateral nuclei (VMN and LN), exerts a phasic effect on a formation of the primary response of the visual cortex evoked by a test light flash. In the initial period of their action, the hypothalamo-cortical responses (1-43 msec for the VMN and 1-10 msec for the LN) completely inhibit the formation of the response of the visual cortex to the light stimulus, while in the second period (43-130 msec for the VMN and 10-150 msec for the LN, respectively), selectively and highly significantly facilitate the formation of the positive phase of the primary response. In the process the negative component is suppressed, and more significantly and longer with stimulation of the VMN than of the LN (140 and 50 msec, respectively). The data obtained make it possible to hypothesize the existence of a highly organized apparatus of phasic hypothalamic (both from the VMN and the LN) control of the function of the visual cortex which is realized both by means of a facilitatory axosomatic mechanism at the level of the dendrites of the basal neurons of layer IV of the cortex and by means of a suppressant mechanism at the level of the apical dendrites of the surface layers of the cortex.
An electrographic correlate of short-latent processes in the visual system corresponding to the ERG a-wave was detected in chronic experiments on awake rabbits. The formation of an early negative potential (ENP), small in amplitude, that precedes the positive component of the primary responses (PR) to light and is thus the earliest signal concerning the arrival of information from the retina was detected during a special recording regimen in the optic tract, superior colliculi, outer geniculate body, and visual cortex. The shift in the latent periods with respect to the onset of the development of the ERG a-wave comprised 2-3 msec in all the above structures. The suppression of all ERG components except the a-wave by glycine injected into the vitreous body was accompanied in all structures by the suppression of all PR components except the very initial ENR. Since the pre-excitatory inhibition of ganglionic elements corresponds to the ERG a-wave at the exit from the retina, the role of this inhibition in the transmission of information concerning the very first instant of the visual signal both to subcortical centers and the visual region of the cerebral cortex should be recognized.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.