The answer to the second question will enable us to provide a similar estimate for the cervical enlargement, and thus determine the proportion of projection cells that belong to the spinothalamic tract at this level.
According to this model, the number and proportion of projection neuron subtypes in a cortical radial column are related to the number of RG progenitors that are present at the onset of neurogenesis, as well as to the number of VZ (apical) and SVZ (basal) proliferative and neurogenic divisions (Huttner and Kosodo, 2005, Noctor et al., 2001, Noctor et al., 2007).
That the smooth interior walls correspond to the different proportions of projection screens in two famous movie theaters, one in New York and one in Berlin, is neither here nor there, but at least it doesn't interfere with the impressive sculptural interplay of inside and outside.
For each projection, a region-of-interest was created based on the proportion of the projection expected to penetrate skin from fluorescent dye studies [11] and ratios of amount of coating on each projection tip as compared with the whole projection were taken.
Thus, even assuming the uncommonly high connectivity level of the examined data set (which likely reflects a lack of probing for absent projections in the literature, rather than a genuinely increased proportion of present projections), a uniform increase of present projections would still yield a correlation between node degree and structural type of ρ = −0.37, p < 0.01.
Further quantification of ipsilateral and contralateral cells in the retina under retrograde labeling experiment shows a smaller proportion of ipsilateral projections at E15.5 E17.5, but a higher fraction of ipsilateral projections at E18.5, suggesting Nr-CAM is a late-stage contralateral-specific cue (Williams et al., 2006).
We also found an inverse relation between structural type and the proportion of long projections, such that areas of a lower structural type had a higher proportion of long projections than areas of a higher structural type (JT = −2.9, p < 0.01).
A perhaps more probable proportion of present projections, such as 60%%, would result in a correlation of ρ = −0.44, p < 0.01.
We verified that, if this proportion was equal across all structural types, the correlation we observed between node degree and structural type would remain moderate and significant up to an added proportion of present projections of 87%%.
By contrast, the relative proportion of present projections was not correlated with |Δlevel| (ρ = −0.36, p > 0.05, Fig. 4c), indicating that the level difference between areas within the hierarchy proposed by Scannell et al. (1995) does not contain information about whether two areas are connected by an anatomical projection.
When we compared aggregate node connection ranges for all areas of a given structural type across all five possible types, we found a positive relation for the proportion of short projections, such that areas of a higher structural type had higher proportions of short-range connections than areas of a lower structural type (JT = 3.1, p < 0.01).
