Post by Amtram on Mar 17, 2014 12:19:00 GMT -5
Thomas Insel, director of the NIMH, put up a great article about the brain, updated from last year with new information. Here's a piece, but check the site for links to information about mental health and the brain.
A few numbers can help to define the challenge. The human brain is thought to have close to 86 billion neurons, each making on average about 10,000 connections. In contrast to most animals, our brains are largely made up of a heavily folded cortex, accounting for 80 percent of brain mass and about 100,000 miles of axons that provide the highways between neurons.1
How many different kinds of neurons are there in the brain? We really don’t know. Unlike the heart or kidney, which have a small, defined set of cell types, we still do not have a taxonomy of neurons, and neuroscientists still argue whether specific types of neurons are unique to humans. But there is no disputing that neurons are only about 10 percent of the cells in the human brain. Most of our brain cells are glial cells, once thought to be mere support cells, but now understood as having a critical role in brain function. Glial cells in the human brain are markedly different from glial cells in other brains, suggesting that they may be important in the evolution of brain function. As one hint to their function, astrocytes, which are one form of glial cell, have been reported recently to “eat” synapses in the brain, providing a critical new mechanism for brain plasticity.2
How does the brain work? Again, we really don’t know. We have a very detailed understanding of how the heart pumps and the kidney filters, but how the brain encodes, stores, and retrieves information is still largely a mystery. We have known for over a century that most of the cortex is organized horizontally into six precise layers, and much of the cortex has vertical mini-columns, but how this matrix of horizontal and vertical structures computes information is not really clear.
Neuroscientists talk a lot about brain circuits. In fact, the word “circuit” is probably misleading. We do not know where most circuits begin and end. And unlike an electrical circuit, brain connections are heavily reciprocal and recursive, so that a direction of information flow can be inferred but sometimes not proven. We believe there are “emergent properties” of the brain that convert electrical signals into memories or dreams, but how this happens is still a mystery. Recent studies have shown that diffuse waves of synchronization across the brain may be critical for attention or learning, but we are just learning about these slow waves of activity, and whether they occur at the “speed of thought” is still debated.3
How many different kinds of neurons are there in the brain? We really don’t know. Unlike the heart or kidney, which have a small, defined set of cell types, we still do not have a taxonomy of neurons, and neuroscientists still argue whether specific types of neurons are unique to humans. But there is no disputing that neurons are only about 10 percent of the cells in the human brain. Most of our brain cells are glial cells, once thought to be mere support cells, but now understood as having a critical role in brain function. Glial cells in the human brain are markedly different from glial cells in other brains, suggesting that they may be important in the evolution of brain function. As one hint to their function, astrocytes, which are one form of glial cell, have been reported recently to “eat” synapses in the brain, providing a critical new mechanism for brain plasticity.2
How does the brain work? Again, we really don’t know. We have a very detailed understanding of how the heart pumps and the kidney filters, but how the brain encodes, stores, and retrieves information is still largely a mystery. We have known for over a century that most of the cortex is organized horizontally into six precise layers, and much of the cortex has vertical mini-columns, but how this matrix of horizontal and vertical structures computes information is not really clear.
Neuroscientists talk a lot about brain circuits. In fact, the word “circuit” is probably misleading. We do not know where most circuits begin and end. And unlike an electrical circuit, brain connections are heavily reciprocal and recursive, so that a direction of information flow can be inferred but sometimes not proven. We believe there are “emergent properties” of the brain that convert electrical signals into memories or dreams, but how this happens is still a mystery. Recent studies have shown that diffuse waves of synchronization across the brain may be critical for attention or learning, but we are just learning about these slow waves of activity, and whether they occur at the “speed of thought” is still debated.3