Introducing the brain: special pyramidal neurons (Introduction)

by David Turell , Thursday, July 14, 2022, 15:31 (863 days ago) @ David Turell

Only in primates:

https://elifesciences.org/articles/79839?utm_source=twitter&utm_medium=social&u...

"it has been reported that the axons of some pyramidal neurons in the mammalian cortex emerge from dendrites rather than from the base of the soma

"These ‘axon carrying dendrites’ are unusual because the signals dendrites receive are usually processed in the soma before they are sent out via the axon to other neurons (Förster, 2014). These kinds of morphological differences are important because they influence how individual neurons and neuronal groups compute information. Researchers are particularly interested in features that only occur in humans and primates, as these may be associated with cognitive behaviors as well as neurological and psychiatric conditions. Now, in eLife, Petra Wahle from Ruhr University Bochum and co-workers in Germany, Austria and Spain report that the proportion of axon carrying dendrites (AcDs) varies between mammalian species and different areas of the brain (Wahle et al., 2022)

"Wahle et al. used a range of histological techniques to compare the morphology and structure of pyramidal neurons in postmortem tissue samples extracted from six cortical areas at different stages of the animals’ development (Figure 2). This revealed that the proportion of pyramidal neurons with an AcD was around 10–20% in non-primate mammals (rat, cat and ferret), but much lower (typically a few percent) in macaque monkeys and humans. Moreover, AcDs were rarely found in the upper layers of the neocortex: these layers are thicker in non-human primates and humans, and are associated with complex behaviors and higher cortical functions. (my bold)

"So, what might be the reason for humans and non-human primates having fewer AcDs? It is thought that AcDs enhance the electrical behavior of pyramidal neurons by allowing signals to bypass the soma and flow directly from the dendrite to the axon. This is supported by prior studies showing that AcDs generate stronger and more frequent electrical spikes, and also require a lower threshold to trigger an action potential (Thome et al., 2014; Kole and Brette, 2018). Wahle et al. propose that humans and non-human primates have fewer AcDs because they already have other cellular specializations that can boost the strength of the electrical signal sent through pyramidal neurons.

"So, what might be the reason for humans and non-human primates having fewer AcDs? It is thought that AcDs enhance the electrical behavior of pyramidal neurons by allowing signals to bypass the soma and flow directly from the dendrite to the axon. This is supported by prior studies showing that AcDs generate stronger and more frequent electrical spikes, and also require a lower threshold to trigger an action potential (Thome et al., 2014; Kole and Brette, 2018). Wahle et al. propose that humans and non-human primates have fewer AcDs because they already have other cellular specializations that can boost the strength of the electrical signal sent through pyramidal neurons. (My bold)

***

"Third, consistent with previous work on the hippocampus (Benavides-Piccione et al., 2020), Wahle et al. found that humans had more pyramidal neurons with AcDs in this region of the brain than mice – which is the opposite of what happens in other parts of the cortex. Wahle et al. suggest that this could be because the hippocampus of humans and non-human primates requires extra features to carry out its complex memory-related processes." (my bold)

Comment: in the progression of brain development by simple evolution from simpler forms this is distinctly different. In regions for higher cognitive abilities there are marked very precise differences in neurons. This is a strong ability for design, and certainly not by chance.