Introducing the brain: right/ left lobe asymmetry (Introduction)

by David Turell @, Friday, February 14, 2020, 19:22 (3 days ago) @ David Turell

A new study comparing humans and apes:

https://medicalxpress.com/news/2020-02-left-brains.html

"The left and right sides of the human brain are specialized for some cognitive abilities. For example, in humans, language is processed predominantly in the left hemisphere, and the right hand is controlled by the motor cortex in the left hemisphere. The functional lateralization is reflected by morphological asymmetry of the brain. Left and right hemisphere differ subtly in the distribution of nerve cells, their connectivity and neurochemistry.

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"Asymmetries of outer brain shape are even visible on endocasts. Most humans have a combination of a more projecting left occipital lobe (located in the back of the brain) with a more projecting right frontal lobe. Brain asymmetry is commonly interpreted as crucial for human brain function and cognition because it reflects functional lateralization.

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"The team found that the magnitude of asymmetry was about the same in humans and most great apes. Only chimpanzees were less asymmetric, on average, than humans, gorillas and orangutans. The researchers also investigated the pattern of asymmetry and could demonstrate that not only humans, but also chimpanzees, gorillas and orangutans showed the asymmetry pattern previously described as typically human: the left occipital lobe, the right frontal lobe, as well as the right temporal pole and the right cerebellar lobe projecting more relatively to their contralateral parts.

"Philipp Mitteroecker, a co-author of the study, says, "What surprised us even more was that humans were least consistent in this asymmetry, with a lot of individual variation around the most common pattern." The authors interpret this as a sign of increased functional and developmental modularization of the human brain. For example, the differential projections of the occipital lobe and the cerebellum are less correlated in humans than in great apes. This finding is interesting because the cerebellum in humans underwent dramatic evolutionary changes and it seems that thereby its asymmetry was affected as well.

"The finding of a shared asymmetry pattern but greater variability in humans is intriguing for the interpretation of human brain evolution. An endocast of one of our fossil ancestors that shows this asymmetry can no longer be interpreted as evidence for human-specific functional brain lateralization without other (archaeological) data. Philipp Gunz, a co-author of the study, explains: "This shared asymmetry pattern of the brain evolved already before the origin of the human lineage. Humans seem to have built upon this morphological pattern to establish functional brain lateralization related to typical human behaviors.'"

Comment: Since the human brain comes with an overall shrinkage mechanism as it complexifies, and it also has a local enlargement mechanism for specific areas, these findings are not unusual. Note the comment about the cerebellum which made large changes from the apes.

See the following:

https://www.sciencedirect.com/science/article/pii/S0960982214010690

"The human cerebellum, however, contains four times more neurons than the neocortex [2] and is attracting increasing attention for its wide range of cognitive functions. Using a method for detecting evolutionary rate changes along the branches of phylogenetic trees, we show that the cerebellum underwent rapid size increase throughout the evolution of apes, including humans, expanding significantly faster than predicted by the change in neocortex size. As a result, humans and other apes deviated significantly from the general evolutionary trend for neocortex and cerebellum to change in tandem, having significantly larger cerebella relative to neocortex size than other anthropoid primates. These results suggest that cerebellar specialization was a far more important component of human brain evolution than hitherto recognized and that technical intelligence was likely to have been at least as important as social intelligence in human cognitive evolution. Given the role of the cerebellum in sensory-motor control and in learning complex action sequences, cerebellar specialization is likely to have underpinned the evolution of humans’ advanced technological capacities, which in turn may have been a preadaptation for language."

Comment: The great apes shared in some of this enlargement, but it played ca great role in our superior evolutionary result.


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