[The corticofugal pathways of the visual system].
Cortical neurons belonging to the same topological ensemble send axons to thalamic and mesencephalic structures and also to contra and ipsilateral cortical areas. The projections are called the corticofugal system. This review addresses the organization and the functions of the efferent cortical fibers within the visual network. For example, the cortico-geniculate fibers participate in shaping the structure of the concentric receptive fields of geniculate cells. Namely, the size of the surround area depends on descending impulses from the cortex. By contrast, cortico-mesencephalic fibers have a more global influence on visual responses. Following the interruption of cortical activity all responses to visual stimuli decline; although in rodents and lagomorphs cortical inactivation does not eliminate those visual responses that are sent to the superior colliculus or pretectum directly from the retina. In each hemisphere it has been demonstrated that contra-lateral cortico-cortical fibers participate in the continuity of the two visual hemi-fields, as the interruption of the callosal impulses results in a truncated field in which the contralateral part of the receptive field is missing., overlaps the vertical meridian is missing. Finally, ipsilateral cortico-cortical fibers allow a consolidation of visual properties of cortical cells. It must be added that there are considerable differences among species in the organization of cortico-cortical relationships. However, this survey seems to indicate that all corticofugal axons are excitatory.
Molotchnikoff
S
S
Département de Sciences Biologiques, Université de Montréal, P.Q.
D000818:Animals; D002540:Cerebral Cortex / Q000032:analysis / Q000502:physiology*; D004525:Efferent Pathways / Q000033:anatomy & histology / Q000502:physiology; D008636:Mesencephalon / Q000033:anatomy & histology / Q000502:physiology; D013788:Thalamus / Q000033:anatomy & histology / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology*; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology
Les voies corticofuges du système visuel.