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I want to know if qualitative experiments have been done growing chimpanzee neurons and human neurons in vitro and have any differences emerged, such as the amount of connections per neuron or anything else.

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  • $\begingroup$ it is not a single neuron per se that makes the difference.. it is the neural network. The basic neuron structure is same in humans and hydra (just that hydra has smaller repertoire of neurotransmitters) $\endgroup$ – WYSIWYG Aug 18 '14 at 6:40
  • $\begingroup$ The claim that it is not a single neuron has nothing to do with what I'm asking (and is also not consensus AFAIK). I'm asking whether there are global differences, such as amount of connections, which are discernable in vitro. $\endgroup$ – Uri Aug 18 '14 at 10:01
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I have came across several studies indicating large similarities between chimpanzee and humans. A study by Bianchi et al., 2013 used immunohistochemistry, electron microscopy, and Golgi staining to characterise synaptic density and dendritic morphology of pyramidal neurons in primary somatosensory (area 3b), primary motor (area 4), prestriate visual (area 18), and prefrontal (area 10) cortices of developing chimpanzees (Pan troglodytes). They found that synaptogenesis occurs synchronously across cortical areas, with a peak of synapse density during the juvenile period (3–5 y). Moreover, similar to findings in humans, dendrites of prefrontal pyramidal neurons developed later than sensorimotor areas. These results suggest that evolutionary changes to neocortical development promoting greater neuronal plasticity early in postnatal life preceded the divergence of the human and chimpanzee lineages. This study however does note that

Despite sharing these neurodevelopmental similarities, it is important to note that cognitive ontogeny in chimpanzees differs from humans in several respects. Behavioral studies suggest that the different social and environmental contexts in which humans and chimpanzee develop may have also been important in the evolution of human-specific socio-cognitive abilities. For example, whereas young chimpanzees do not fully wean until 4–5 y of age and remain closely attached to their mothers during the early years of development, human infants often interact with multiple caregivers and engage in joint attention.

In another study by Bianchi et al., also published in 2013 regional variation in the morphology of pyramidal neurons in the cerebral cortex of great apes, humans' closest living relatives were investigated. The study used the rapid Golgi stain to quantify the dendritic structure of layer III pyramidal neurons in 4 areas of the chimpanzee cerebral cortex: Primary somatosensory (area 3b), primary motor (area 4), prestriate visual (area 18), and prefrontal (area 10) cortex. The study showed that

Consistent with previous studies in humans and macaque monkeys, pyramidal neurons in the prefrontal cortex of chimpanzees exhibit greater dendritic complexity than those in other cortical regions, suggesting that prefrontal cortical evolution in primates is characterized by increased potential for integrative connectivity.

However

Compared with chimpanzees, the pyramidal neurons of humans had significantly longer and more branched dendritic arbors in all cortical regions.

These studies show that despite significant morphological and developmental similarities between human and chimpanzee neurons, there are still notable observable differences.

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