Attentional activation of the visual thalamic reticular nucleus depends on'top-down' inputs from the primary visual cortex via corticogeniculate pathways

This study is concerned with corticothalamic neural mechanisms underlying a ttentional phenomena. Previous results from this laboratory demonstrated th at the visual sector of the GABAergic thalamic reticular nucleus is activat ed by attention in rats. Here it is demonstrated that Fos-detected activati on of the visual reticular sector in rats, induced by attentive exploration of a novel-complex environment, is dependent on 'top-down' cortical inputs from the primary visual cortex: on the basis (a) that activation of the vi sual reticular sector is drastically diminished after ibotenate lesions mos tly restricted to layer 6 of the primary visual cortex, which gives origin to the corticogeniculate pathway that innervates both the visual reticular sector and the dorsal lateral geniculate nucleus; and (b) the lesions did n ot induce retrograde degeneration nor diminution of Fos label in the genicu late. The results are consistent with the previously proposed hypothesis th at a focus of attention in V1 generates a column of increased thalamocortic al transmission in LGN by means of monosynaptic glutamatergic corticogenicu late inputs, and decreased transmission of surrounding regions by disynapti c cortico-reticulo-geniculate (ultimately GABAegic) inputs. The results als o suggest that attentional modulation of thalamocortical transmission is a main function of corticothalamic pathways to sensory relay nuclei. (C) 2000 Elsevier Science B.V. All rights reserved.