Abstract
Pyramidal neurons are the most common neurons in the cerebral cortex. Understanding how they differ between species is a key challenge in neuroscience. We compared human temporal cortex and mouse visual cortex pyramidal neurons from the Allen Cell Types Database in terms of their electrophysiology and dendritic morphology. We found that, among other differences, human pyramidal neurons had a higher action potential threshold voltage, a lower input resistance, and larger dendritic arbors. We learned Gaussian Bayesian networks from the data in order to identify correlations and conditional independencies between the variables and compare them between the species. We found strong correlations between electrophysiological and morphological variables in both species. In human cells, electrophysiological variables were correlated even with morphological variables that are not directly related to dendritic arbor size or diameter, such as mean bifurcation angle and mean branch tortuosity. Cortical depth was correlated with both electrophysiological and morphological variables in both species, and its effect on electrophysiology could not be explained in terms of the morphological variables. For some variables, the effect of cortical depth was opposite in the two species. Overall, the correlations among the variables differed strikingly between human and mouse neurons. Besides identifying correlations and conditional independencies, the learned Bayesian networks might be useful for probabilistic reasoning regarding the morphology and electrophysiology of pyramidal neurons.
Highlights
Rel depth had a strong positive marginal (0.59) and partial correlation with up down ratio (0.53) and a strong negative one with threshold (−0.40). This is contrary to the results of Deitcher et al (2017) who found that human electrophysiological features such as input resistance and membrane time constant were independent of depth in the human L2/3 pyramidal neurons of the temporal cortex and, on the other hand, is partially consistent with the results of Kalmbach et al (2018)
We found strong differences between the electrophysiology and morphology of human and mouse pyramidal neurons, both in terms of the variables’ magnitudes and in terms of correlations between the variables, as evidenced by the differences in their Bayesian networks
Electrophysiological variables were correlated with morphological variables that are directly related to dendritic arbor size or diameter, and to branchlevel variables such as mean bifurcation angle and mean tortuosity
Summary
A key challenge in neuroscience is to understand how pyramidal neurons differ across species and cortical regions (Elston et al, 2001; Jacobs and Scheibel, 2002; Benavides-Piccione et al, 2006; Bianchi et al, 2013; Mohan et al, 2015; Gilman et al, 2017; Luebke, 2017) They are often compared in terms of their dendritic morphology, since it directly influences neuronal computation (Häusser et al, 2000; Segev and London, 2000; Spruston, 2008). The pyramidal neurons of the monkey visual cortex have smaller basal dendrites than those of its prefrontal cortex, while there is no significant difference in the mouse (Gilman et al, 2017). Deitcher et al (2017) found that the morphology of human pyramidal neurons varies with the somatic distance from the pia while that of mouse neurons does not
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