The Topographic Organization and Axis of Projection within the Visual Sector of the Rabbit's Thalamic Reticular Nucleus

Abstract

The organization of the visual field representation within the thalamic reticular nucleus (TRN) of the rabbit was studied. Focal injections of horseradish peroxidase (HRP) and/or [3H]proline were made into visuocortical areas V1 and V2 and the dorsal lateral geniculate nucleus (dLGN). The resultant labelling in the thalamus was analysed. A single injection in V1 or V2 results in a single zone of terminal label within the TRN that is restricted to the dorsocaudal part of the sheet-like nucleus. In comparisons of the zones of label following injections at two different cortical sites in V1, a medial to lateral shift in label across the thickness of the TRN sheet is accompanied by a medial to lateral shift in label in the dLGN; a dorsal to ventral shift in label within the plane of the TRN sheet is accompanied by a dorsal to ventral shift in label in the dLGN. Thus, like the dLGN the TRN receives a precise topographic projection from V1. In reconstructions from horizontal sections the zones of label within the TRN resemble 'slabs', which lie within the plane of the nucleus parallel to its borders. Thus, the slabs of visuocortical terminals and reticular dendrites are similarly oriented. As revealed by the orientation of the slabs, the lines of projection representing points in visual space are represented by the oblique rostrocaudal dimension of the TRN. Injections restricted to V1 produce terminal labelling that is confined to the outer two-thirds of the TRN across its thickness, whilst those involving V2 result in terminal labelling within the inner one-third of the nucleus. Thus, the adjacent cortical areas V1 and V2 project in a continuous fashion across the mediolateral dimension of the TRN. The organization of the map within the TRN, which was revealed by visuocortical injections, was confirmed by the pattern of retrograde labelling within the nucleus following geniculate injections of HRP. On the basis of these findings and those in other mammalian species, two major conclusions can be reached that alter our view of the TRN. First, rather than mapping onto the whole nucleus in a continuous fashion, the cortical projection to the TRN has significant discontinuities. Second, rather than integrating efferents from widespread cortical areas, the reticular dendrites are related to focal areas of cortex.

Prefrontal Projections to the Thalamic Reticular Nucleus form a Unique Circuit for Attentional Mechanisms

“…In rats, cats, rabbits, and primates, cortical and thalamic afferents in TRN are topographically organized (Crabtree and Killackey, 1989;Cicirata et al, 1990;Conley and Diamond, 1990;Cornwall et al, 1990;Crabtree, 1992aCrabtree, ,b, 1996Crabtree, , 1998Crabtree, , 1999Lozsadi, 1994Lozsadi, , 1995Ilinsky et al, 1999). Along the rostrocaudal axis, centroposterior loci in TRN are respectively linked with the somatosensory, visual, and auditory cortices and their associated thalamic nuclei.…”

Organization in the somatosensory sector of the cat's thalamic reticular nucleus

“…However, in sensory sectors in caudal and ventral TRN, cortical inputs form various maps that deviate considerably from those that would be expected from a sheet-to-sheet corticoreticular relationship (Montero et al, 1977;Crabtree and Killackey, 1989;Conley and Diamond, 1990;Conley et al, 1991;Crabtree, 1992a,b). Some of these maps are oriented perpendicular to the plane of TRN because one of the axes of each of these maps extends across the thickness of the nucleus.…”

“…Some of these maps are oriented perpendicular to the plane of TRN because one of the axes of each of these maps extends across the thickness of the nucleus. These maps include one in the rabbit's visual sector, which receives retinotopically accurate inputs from V1 (Montero et al, 1977;Crabtree and Killackey, 1989), and ones in the somatosensory sector of the rabbit (Crabtree, 1992a) and the cat (Crabtree, 1992b), which receive somatotopically accurate inputs from somatosensory cortical area 1 61). Because of the perpendicular orientation of these maps, slab-like organizational components representing terminals from local areas of cortex extend parallel to the plane of TRN and occupy only a fraction of its thickness (Crabtree and Killackey, 1989;Crabtree, 1992a,b).…”

Brain bases of the automaticity via visual search task

“…It is known that rs-FC networks are consistent, and that the connectivity values within nodes of the same network are high, however, it is low whenever connections between nodes of different networks is explored (Damoiseaux et al, 2006;Smith, et al, 2009;. One of the most influential works on visual attention and rs-FC linked the bottom-up processing of the visual scene with to the ventral attention network and the top-down influences to the dorsal attention network .…”

“…It is known that rs-FC networks are consistent, and that the connectivity values within nodes of the same network are high, however, it is low whenever connections between nodes of different networks is explored (Damoiseaux et al, 2006; Smith, et al, 2009;. One of the most influential …”