Comprehensive Morpho-Electrotonic Analysis Shows 2 Distinct Classes of L2 and L3 Pyramidal Neurons in Human Temporal Cortex

Abstract

There have been few quantitative characterizations of the morphological, biophysical, and cable properties of neurons in the human neocortex. We employed feature-based statistical methods on a rare data set of 60 3D reconstructed pyramidal neurons from L2 and L3 in the human temporal cortex (HL2/L3 PCs) removed after brain surgery. Of these cells, 25 neurons were also characterized physiologically. Thirty-two morphological features were analyzed (e.g., dendritic surface area, 36 333 ± 18 157 μm2; number of basal trees, 5.55 ± 1.47; dendritic diameter, 0.76 ± 0.28 μm). Eighteen features showed a significant gradual increase with depth from the pia (e.g., dendritic length and soma radius). The other features showed weak or no correlation with depth (e.g., dendritic diameter). The basal dendritic terminals in HL2/L3 PCs are particularly elongated, enabling multiple nonlinear processing units in these dendrites. Unlike the morphological features, the active biophysical features (e.g., spike shapes and rates) and passive/cable features (e.g., somatic input resistance, 47.68 ± 15.26 MΩ, membrane time constant, 12.03 ± 1.79 ms, average dendritic cable length, 0.99 ± 0.24) were depth-independent. A novel descriptor for apical dendritic topology yielded 2 distinct classes, termed hereby as “slim-tufted” and “profuse-tufted” HL2/L3 PCs; the latter class tends to fire at higher rates. Thus, our morpho-electrotonic analysis shows 2 distinct classes of HL2/L3 PCs.

Comparing basal dendrite branches in human and mouse hippocampal CA1 pyramidal neurons with Bayesian networks

“…Nonetheless, inter-species differences in the magnitude of length and tortuosity were more pronounced in terminal branches than in non-terminal ones, as evidenced by the lack of difference at some branch orders in the latter (Section 3.3). A similar result has been observed regarding the branch length of basal dendrites of temporal cortex pyramidal neurons of the human and the mouse 13 .…”

“…They are often compared in terms of their dendritic morphology, a feature which directly influences neuronal computation [6][7][8] . However, dendritic morphology varies across layers and cortical regions within a single species 4,[9][10][11][12][13] (more so in primates than in rodents 1,2 ), possibly as an adaptation to their different cytoarchitectonic and functional features. It is thus important to compare neurons from homologous regions of the two species.…”

Quantitative synapse analysis for cell-type specific connectomics

“…L2 Pyr soma surface area varied more than 2-fold, consistent with prior observations that neocortical pyramidal neurons can have different mean soma sizes (van Aerde and Feldmeyer, 2015) associated with distinct developmental origins and projection targets (Deitcher et al, 2017;Tyler et al, 2015;Yamashita et al, 2013;Zaitsev et al, 2012). Soma puncta density was not correlated with soma size, although higher somatic and dendritic puncta densities were positively correlated (Supplemental Figure S3H-J).…”

Toward an integrated classification of neuronal cell types: morphoelectric and transcriptomic characterization of individual GABAergic cortical neurons

“…Before morphological feature analysis, reconstructed neuronal morphologies were expanded in the dimension perpendicular to the cut surface to correct for shrinkage (Deitcher et al, 2017;Egger et al, 2008) after processing. The amount of shrinkage was calculated by comparing the distance of the soma to the cut surface during recording and after fixation and reconstruction.…”