Evolution of Neocortex

Branched projections in the auditory thalamocortical and corticocortical systems

“…In the somatic sensory thalamus, the thalamic cells labeled by unmapped SI and SII injections form concentric rings: the core, in the ventroposterior medial nucleus (VPM) contains only a projection to the primary somatosensory cortex (SI); an inner shell projects to areas SI and SII, and has branched projections to both; and an outer shell region has the same types of labeling but with a coarser topography (Spreafico et al, 1981). The latter authors suggested that secondary, ostensibly less topographic areas arose earlier in evolution (Diamond and Hall, 1969), and that BAs may contribute to the emergence of precise, topographic connections. However, such circumscribed regions of labeling are not readily apparent in the MGB, perhaps because AI and AAF are at the same hierarchical level of processing (Rouiller et al, 1991), because all AC extrinsic connections are topographic , or because the tracers we used may be more sensitive.…”

Neurotransmitter organization and connections of turtle cortex: implications for the evolution of mammalian isocortex

“…Further, there has been a clear trend within various mammalian orders toward an increase in cortical surface area and an increase in the number of functionally defined areas of isocortex. As noted above, among "primitive" living mammals such as insectivores, marsupials and monotremes, a somatosensory region, two visual regions and an auditory region are typically present (Diamond and Hall, 1969;Lende, 1969;Nauta and Karten, 1970;Diamond, 1976;Bohringer and Rowe, 1977;Johnson, 1977;Morgane et al, 1986;Kaas, 1989). Thus, as few as four distinct sensory/motor areas may have been present in the mammals ancestral to modern mammals.…”

Signal processing in the tectothalamic pathway.

“…Blindsight is thought to be mediated by projections from the superior colliculus and/or pretectum to the pulvinar nucleus. This is supported by the fact that in species with expanded tectopulvinar pathways, such as the tree shrew, animals maintain a large degree of visual capacity after complete lesion of VI and subsequent degeneration of the dLGN (Diamond and Hall, 1969;. These studies, as well as studies of human blindsight, suggest that a substantial amount of visual information passes through structures other than the primary visual pathway through the dLGN to VI, and that this information can be utilized to evaluate visual signals and initiate appropriate responsive actions.…”

“…12B), although our results do not rule out the possibility that these projections arise from different cell types located adjacent to one another. Evidence for collateral projections was provided by Diamond and Hall (1969) who noted that large lesions of the tree shrew temporal cortex produced widespread degeneration of pulvinar neurons, but little discernable degeneration was observed following small lesions in the temporal cortex. (Kaufman et al 1984;Cusick et al 1985;Tong and Spear 1986;Miceli et al 1991).…”

“…Traditionally, the retino-tecto-thalamocortical pathways have been considered secondary visual pathways that relay ascending sensory signals in parallel with the primary retino-geniculocortical pathways (Diamond and Hall 1969;Schneider 1969). Our anatomical results support the idea that the Pd and Pc are "second order" nuclei (Masterson et al 2009a) that relay visual information from the SC to the temporal cortex, and that the activity of the Pd and Pc is modulated by the temporal cortex directly via layer VI corticothalamic projections, as well as indirectly via layer V corticotectal projections (Fig.…”