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2 Will we ever be able to regenerate the brain?
JEAN LIVET
WILL WE EVER BE ABLE TO REGENERATE THE BRAIN?
YOU were born with all the brain cells you’ll ever have, so the saying goes. So much for sayings. In the 1990s, decades of dogma were overturned by the discovery that mammals, including people, make new neurons throughout their lives. In humans, such “neurogenesis” has been seen in two places: neurons formed in the olfactory bulb seem to be involved in learning new smells, while those born in the hippocampus are involved in learning and memory. The discovery that new neurons can integrate into the adult brain raises intriguing possibilities. Could the process be harnessed to treat diseases of the brain, such as Parkinson’s and Alzheimer’s? The trick will be in replacing diseased cells with just the right kind of neuron, says Jeff Macklis, who
“WHEN you’re smilin’, the whole world smiles with you,” sang Louis Armstrong. He could have been referring to what some consider one of the greatest recent discoveries of neuroscience: mirror neurons. Discovered in macaques in the 1990s, these cells were spotted when researchers made recordings from microelectrodes placed in the animals’ brains as they performed various tasks. While many neurons fired when the animal performed an action, a subset also fired when the animals saw the researcher perform the same action, with different groups of mirror neurons for different actions. Neuroscientists have speculated that in people, mirror neurons could represent the neural basis of empathy. They could also contribute to imitation and learning, and perhaps even language acquisition. It has been hard to find out if people have mirror neurons, but MRI scans have shown that certain areas of the brain – dubbed mirror systems – “light up” when we perform and watch the same action. Numerous studies have shown that people with more activity in their mirror systems seem to be better at understanding other people’s emotions.
studies neurogenesis at the Massachusetts Institute of Technology. By some estimates, the nervous system is made up of 10,000 different kinds of neuron. This complexity means you can’t just hijack any old cell produced by natural neurogenesis. However, there may be other ways of growing new neurons to order. Olle Lindvall at Lund University in Sweden has shown what might be possible. He transplanted dopamineproducing neurons taken from aborted fetuses into the brains of people with Parkinson’s, and showed the new neurons can improve brain function, although the treatment didn’t work for everyone. Lindvall is now looking for ways to make these specialised neurons from embryonic stem cells or stem cells made by
Conversely, less activity in mirror systems has been linked to autism and also with psychopathy – different conditions that are both noted for low levels of empathy. Nina Bien’s team at Maastricht University in the Netherlands recently identified inhibition mechanisms that hint at how we can mentally imitate an action without actually performing it (Cerebral Cortex, vol 19, p 2338). Nevertheless, some researchers question whether mirror systems can take sole responsibility for empathy. “Understanding someone else’s actions and empathy are huge cognitive achievements,” says Cecilia Heyes, a psychologist at the University of Oxford. “So to suggest that there’s one discrete neural system responsible for it doesn’t make sense.” However, Marco Iacoboni, a neuroscientist at the University of California, Los Angeles, claims to have seen individual brain cells behaving like mirror neurons in people. He made his observations when someone with epilepsy was undergoing exploratory brain surgery to investigate the cause of their seizures. The results are due to be published this month in Current Biology. Helen Thomson
2
reprogramming adult skin cells. And Macklis has found that even in non-neurogenic parts of the brain, there are small numbers of “progenitor cells” left over from brain development in the womb. These are not true stem cells, but they have some neurogenesis capabilities. Macklis has shown that in animals at least, these progenitors can be directed to form functional neurons. In mice, he has found chemical cues that tip progenitors into becoming motor neurons, the cells damaged by motor neuron disease. “I’m a great optimist with respect to regulating neurogenesis in normally non-neurogenic parts of the brain.” says Macklis. “But the nervous system was built with precision, and we will have to rebuild it with that precision.”
James Mitchell Crow
”It was the first time a memory had been traced to the nerve cells that encoded it”
3 April 2010 | NewScientist | 29
WILL WE EVER BE ABLE TO REGENERATE THE BRAIN?
YOU were born with all the brain cells you’ll ever have, so the saying goes. So much for sayings. In the 1990s, decades of dogma were overturned by the discovery that mammals, including people, make new neurons throughout their lives. In humans, such “neurogenesis” has been seen in two places: neurons formed in the olfactory bulb seem to be involved in learning new smells, while those born in the hippocampus are involved in learning and memory. The discovery that new neurons can integrate into the adult brain raises intriguing possibilities. Could the process be harnessed to treat diseases of the brain, such as Parkinson’s and Alzheimer’s? The trick will be in replacing diseased cells with just the right kind of neuron, says Jeff Macklis, who
“WHEN you’re smilin’, the whole world smiles with you,” sang Louis Armstrong. He could have been referring to what some consider one of the greatest recent discoveries of neuroscience: mirror neurons. Discovered in macaques in the 1990s, these cells were spotted when researchers made recordings from microelectrodes placed in the animals’ brains as they performed various tasks. While many neurons fired when the animal performed an action, a subset also fired when the animals saw the researcher perform the same action, with different groups of mirror neurons for different actions. Neuroscientists have speculated that in people, mirror neurons could represent the neural basis of empathy. They could also contribute to imitation and learning, and perhaps even language acquisition. It has been hard to find out if people have mirror neurons, but MRI scans have shown that certain areas of the brain – dubbed mirror systems – “light up” when we perform and watch the same action. Numerous studies have shown that people with more activity in their mirror systems seem to be better at understanding other people’s emotions.
studies neurogenesis at the Massachusetts Institute of Technology. By some estimates, the nervous system is made up of 10,000 different kinds of neuron. This complexity means you can’t just hijack any old cell produced by natural neurogenesis. However, there may be other ways of growing new neurons to order. Olle Lindvall at Lund University in Sweden has shown what might be possible. He transplanted dopamineproducing neurons taken from aborted fetuses into the brains of people with Parkinson’s, and showed the new neurons can improve brain function, although the treatment didn’t work for everyone. Lindvall is now looking for ways to make these specialised neurons from embryonic stem cells or stem cells made by
Conversely, less activity in mirror systems has been linked to autism and also with psychopathy – different conditions that are both noted for low levels of empathy. Nina Bien’s team at Maastricht University in the Netherlands recently identified inhibition mechanisms that hint at how we can mentally imitate an action without actually performing it (Cerebral Cortex, vol 19, p 2338). Nevertheless, some researchers question whether mirror systems can take sole responsibility for empathy. “Understanding someone else’s actions and empathy are huge cognitive achievements,” says Cecilia Heyes, a psychologist at the University of Oxford. “So to suggest that there’s one discrete neural system responsible for it doesn’t make sense.” However, Marco Iacoboni, a neuroscientist at the University of California, Los Angeles, claims to have seen individual brain cells behaving like mirror neurons in people. He made his observations when someone with epilepsy was undergoing exploratory brain surgery to investigate the cause of their seizures. The results are due to be published this month in Current Biology. Helen Thomson
2
reprogramming adult skin cells. And Macklis has found that even in non-neurogenic parts of the brain, there are small numbers of “progenitor cells” left over from brain development in the womb. These are not true stem cells, but they have some neurogenesis capabilities. Macklis has shown that in animals at least, these progenitors can be directed to form functional neurons. In mice, he has found chemical cues that tip progenitors into becoming motor neurons, the cells damaged by motor neuron disease. “I’m a great optimist with respect to regulating neurogenesis in normally non-neurogenic parts of the brain.” says Macklis. “But the nervous system was built with precision, and we will have to rebuild it with that precision.”
James Mitchell Crow
”It was the first time a memory had been traced to the nerve cells that encoded it”
3 April 2010 | NewScientist | 29