Cortical structure predicts the pattern of corticocortical connections

Abstract

Cortical areas are linked through pathways which originate and terminate in specific layers. The factors underlying which layers are involved in specific connections are not well understood. Here we tested whether cortical structure can predict the pattern as well as the relative distribution of projection neurons and axonal terminals in cortical layers, studied with retrograde and anterograde tracers. We used the prefrontal cortices in the rhesus monkey as a model system because their laminar organization varies systematically, ranging from areas that have only three identifiable layers, to those that have six layers. We rated each prefrontal area based on the number and definition of its cortical layers (level 1, lowest; level 5, highest). The structural model accurately predicted the laminar pattern of connections in approximately 80% of the cases. Thus, projection neurons from a higher-level cortex originated mostly in the upper layers and their axons terminated predominantly in the deep layers (4-6) of a lower-level cortex. Conversely, most projection neurons from a lower-level area originated in the deep layers and their axons terminated predominantly in the upper layers (1-3) of a higher-level area. In addition, the structural model accurately predicted that the proportion of projection neurons or axonal terminals in the upper to the deep layers would vary as a function of the number of levels between the connected cortices. The power of this structural model lies in its potential to predict patterns of connections in the human cortex, where invasive procedures are precluded.

Multisensory anatomical pathways

“…It is also possible that the classical anatomical classification of FF and FB projections does not apply to heteromodal projections when it comes to interactions between sensory modalities. This would support the hypothesis according to which the anatomical pattern of the cortico-cortical connections that involve the polysensory areas of the frontal lobe depend on the intrinsic architecture of areas linked together in terms of laminar differentiation (Barbas and Rempel-Clower, 1997;Rempel-Clower and Barbas, 2000). How this rule of a structural dependence about the laminar organization of projections affects heteromodal connections remains to be determined.…”

The Effects of an Alpha-2 Adrenergic Agonist, Guanfacine, on rCBF in Human Cortex in Normal Controls and Subjects with Focal Epilepsy

“…The findings in this group, nevertheless, also agree with our hypothesis of anterior-increase and posterior-decrease in rCBF. Our subjects with temporal lobe epilepsy show frontal-parietal increases as well, although these increases are shifted to the side contralateral to the seizure focus, which may reflect an interaction of the temporal epileptogenic focus with the temporal-frontal connections that go from the middle temporal gyrus to the middle frontal gyrus (Barbas and Rempel-Clower 1997). These results agree with those produced by clonidine as reported by Moffoot et al (1994) in Korsakoff's subjects, but differ from those reported by Coull and colleagues (1997) in controls treated with clonidine.…”

Neuronal and morphological bases of cognitive decline in aged rhesus monkeys

“…In contrast to layer II/ III neurons, none of the electrophysiological signatures of aging among layer V neurons correlate with cognitive performance (Luebke and Chang 2007;Luebke and Amatrudo 2010). Thus, within PFC area 46, it is the layer II/III corticocortical pyramidal neurons, and not the layer V neurons that contribute to the corticostriatal-thalamic-cortical circuitry, that are thought to be crucial for cognitive capacities vulnerable to the effects of aging (Barbas and Rempel-Clower 1997;Luebke and Chang 2007;Luebke and Amatrudo 2010).…”