Neural networks: Why larger brains are more susceptible to mental illnesses

[EdEarl]

 

Phys.org

 

The EDR describes a consistent relationship between distances and connection strength. Consistent with the tracing results, the EDR predicts that there are many fewer long-range axons (nerve fibers that function as transmission lines of the nervous system) than short ones, and this can be quantified by a mathematical equation. At the level of cortical areas (such as visual cortex or auditory cortex) examined by the tracing studies, this means the closer two areas are to each other, the more connections exist between them.

They studied brains of macaque and mouse and found interconnections statically consistent with EDR.

Based on these results, the researchers hypothesize that the EDR describes an effective design principle that remains constant during the evolution of mammalian brains of different sizes. They present mathematical arguments that support the universal applicability of the EDR as a governing principle of cortical connectivity, as well as further experimental support from high-resolution tracer experiments in small brain areas from macaque, mouse, and mouse lemur (a primate with a very small brain).

 

Their results, the researchers conclude, "suggest that the EDR plays a key role across the mammalian order to optimize the layout of the inter-areal cortical network allowing larger-brained animals to maintain communication efficiencies combined with increased neuron numbers".

 

As the EDR predicts and the tracing data here confirm, neuronal connections weaken exponentially with distance. Assuming the EDR can be applied to all mammalian brains, this suggests that long-distance connections could be quite weak in the human cortex, which is approximately five times larger than that of the macaque. If true, the researchers say, one could speculate that the low weight of human long-range connections may contribute to an increased susceptibility to disconnection syndromes, such as have been proposed for Alzheimer disease and schizophrenia".

If their hypothesis is true, elephants and toothed whales, including dolphins and orca, must have mental problems often. If so, have these mental problems been reported? I've not heard of it. Can it be true without us knowing? We have minimal contact with whales, but elephants and people have lived and worked together in the East for a very long time; the people who train and work with elephants have not reported such things, AFAIK.

[DrmDoc]

They studied brains of macaque and mouse and found interconnections statically consistent with EDR.

If their hypothesis is true, elephants and toothed whales, including dolphins and orca, must have mental problems often. If so, have these mental problems been reported? I've not heard of it. Can it be true without us knowing? We have minimal contact with whales, but elephants and people have lived and worked together in the East for a very long time; the people who train and work with elephants have not reported such things, AFAIK.

An interesting article. One might ask why wouldn't there be denser connectivity between closer rather than distant proximity neuronal groups considering the likely contiguous nature of our CNS evolution? Isn't it likely that subsequent neural groups are evolved from and more dependent on immediately prior groups rather than groups immediately prior to those? It seems highly probable that a recently evolved neural group is likely to have more connections with the next nearest evolved group than with a group more distantly evolved. What this study suggests to me is how recently evolved neural groups are more functionally dependent on nearest evolved groups than on those earlier in our brain's evolution.

[Moontanman]

They studied brains of macaque and mouse and found interconnections statically consistent with EDR.

If their hypothesis is true, elephants and toothed whales, including dolphins and orca, must have mental problems often. If so, have these mental problems been reported? I've not heard of it. Can it be true without us knowing? We have minimal contact with whales, but elephants and people have lived and worked together in the East for a very long time; the people who train and work with elephants have not reported such things, AFAIK.

 

 

I was going to say sperm whales must be batshitcrazy but you beat me to it...

[EdEarl]

 

 

I was going to say sperm whales must be batshitcrazy but you beat me to it...

Wish I'd thought of batshitcrazy

[andrewcellini]

but elephants and people have lived and worked together in the East for a very long time; the people who train and work with elephants have not reported such things, AFAIK.

My personal research has concluded that an elephant never forgets.

[DrmDoc]

After another review of the referenced article, I think its claims are extremely premature. The article proposes that larger brains have weaker connections between distant neuronal groups and, therefore, are more susceptible to disconnection syndrome, an effect of Alzheimer and schizophrenia. The article appears to presuppose smaller brains preclude Alzheimer and schizophrenia. Disconnection syndrome is diagnosed as an effect rather than a cause of those conditions. Researchers will have to first establish that smaller brains are not subject to the causes of Alzheimer and schizophrenia in larger brains before suggesting they are not susceptible to the effects arising from those illnesses. If smaller brains are not subject to afflictions of larger brains, size is an insufficient explanation for that variance--in my opinion.