Post by Amtram on Feb 2, 2014 17:45:07 GMT -5
I don't know how much this is common knowledge, so let me say it with the assumption that it's not. Right before birth, a normal human brain experiences some significant synaptic pruning. Major neuronal die-off. Why is this important to know? Because one of the features of autistic brains is that this die-off doesn't happen. The excess of neurons is partly to blame for many autistic symptoms. Not for this thread, though, or at least not the first post. The Scientist published an article that studied the role of microglia in synaptic pruning. (From Neuroscience, Exploring the Brain - Second, a class of cells called microglia function as phagocytes to remove debris left by dead or degenerating neurons and glia.)
The article begins:
The article goes on to explain that too many connections is weaker than a smaller number of connections because it confuses communication. The research was done on mice, so there might not be an exact correlation with humans.
To my mind, the idea that too many neurons weaken the major neuronal pathways kind of makes sense. We have several established pathways in our brains for specific functions, and when there's damage to the brain and the signals that normally use those pathways have to take alternate back routes to get to the same place, it produces a lot of functional problems. Maybe having so many alternate routes already in place makes it easier for signals to get lost along those back roads in the first place, so fewer of the signals "know" to stay to the highway? I'm probably being overly simplistic here, but it fits fairly well with a lot of the other research I've read.
(BTW, that other link is to a Neuroscience textbook that you can download and read for free. Knock yourselves out. It's first-year college level, so it might not be too intimidating, I hope!)
The article begins:
As the brain matures, a group of resident immune cells called microglia crawl between the growing neurons and engulf invading microbes or damaged cells. They are also thought to pluck off some of the synapses that connect different neurons.
This destructive act is important for the developing brain. The microglia prune away weak or unwanted connections, allowing more productive ones to become stronger. Without this “synaptic pruning,” a team of researchers led by Cornelius Gross at the European Molecular Biology Laboratory has shown that mice grow up with weaker connections between different parts of their brains.
“This is one of the few robust features seen in people with autism: their brain regions don’t synchronize well,” said Gross. “We looked and found that these mice have what are typically thoughts to be autism-like behavioral features.” In other words, mice without microglia were more likely to show repetitive movements and to shy away from social contact.
The results, published today (February 3) in Nature Neuroscience, may also provide clues about other brain disorders that involve altered connectivity, including schizophrenia, major depression, and obsessive-compulsive disorder.
This destructive act is important for the developing brain. The microglia prune away weak or unwanted connections, allowing more productive ones to become stronger. Without this “synaptic pruning,” a team of researchers led by Cornelius Gross at the European Molecular Biology Laboratory has shown that mice grow up with weaker connections between different parts of their brains.
“This is one of the few robust features seen in people with autism: their brain regions don’t synchronize well,” said Gross. “We looked and found that these mice have what are typically thoughts to be autism-like behavioral features.” In other words, mice without microglia were more likely to show repetitive movements and to shy away from social contact.
The results, published today (February 3) in Nature Neuroscience, may also provide clues about other brain disorders that involve altered connectivity, including schizophrenia, major depression, and obsessive-compulsive disorder.
To my mind, the idea that too many neurons weaken the major neuronal pathways kind of makes sense. We have several established pathways in our brains for specific functions, and when there's damage to the brain and the signals that normally use those pathways have to take alternate back routes to get to the same place, it produces a lot of functional problems. Maybe having so many alternate routes already in place makes it easier for signals to get lost along those back roads in the first place, so fewer of the signals "know" to stay to the highway? I'm probably being overly simplistic here, but it fits fairly well with a lot of the other research I've read.
(BTW, that other link is to a Neuroscience textbook that you can download and read for free. Knock yourselves out. It's first-year college level, so it might not be too intimidating, I hope!)