Brain signals move paralyzed limbs in new experiment

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To help people suffering paralysis from injury, stroke or disease, scientists have invented brain-machine interfaces that record electrical signals of neurons in the brain and translate them to movement. Usually, that means the neural signals direct a device, like a robotic arm.Cornell University researcher Maryam Shanechi, assistant professor of electrical and computer engineering, working with Ziv Williams, assistant professor of neurosurgery at Harvard Medical School, is bringing brain-machine interfaces to the next level: Instead of signals directing a device, she hopes to help paralyzed people move their own limb, just by thinking about it.When paralyzed patients imagine or plan a movement, neurons in the brain’s motor cortical areas still activate even though the communication link between the brain and muscles is broken. By implanting sensors in these brain areas, neural activity can be recorded and translated to the patient’s desired movement using a mathematical transform called the decoder. These interfaces allow patients to generate movements directly with their thoughts.In a paper published online Feb. 18 in Nature Communications, Shanechi, Williams and colleagues describe a cortical-spinal prosthesis that directs “targeted movement” in paralyzed limbs. The research team developed and tested a prosthesis that connects two subjects by enabling one subject to send its recorded neural activity to control limb movements in a different subject that is temporarily sedated. The demonstration is a step forward in making brain-machine interfaces for paralyzed humans to control their own limbs using their brain activity alone.The brain-machine interface is based on a set of real-time decoding algorithms that process neural signals by predicting their targeted movements. In the experiment, one animal acted as the controller of the movement or the “master,” then “decided” which target location to move to, and generated the neural activity that was decoded into this intended movement. The decoded movement was used to directly control the limb of the other animal by electrically stimulating its spinal cord.”The problem here is not only that of decoding the recorded neural activity into the intended movement, but also that of properly stimulating the spinal cord to move the paralyzed limb according to the decoded movement,” Shanechi said.The scientists focused on decoding the target endpoint of the movement as opposed to its detailed kinematics. This allowed them to match the decoded target with a set of spinal stimulation parameters that generated limb movement toward that target. …


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How chronic stress predisposes brain to mental disorders

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University of California, Berkeley, researchers have shown that chronic stress generates long-term changes in the brain that may explain why people suffering chronic stress are prone to mental problems such as anxiety and mood disorders later in life.Their findings could lead to new therapies to reduce the risk of developing mental illness after stressful events.Doctors know that people with stress-related illnesses, such as post-traumatic stress disorder (PTSD), have abnormalities in the brain, including differences in the amount of gray matter versus white matter. Gray matter consists mostly of cells — neurons, which store and process information, and support cells called glia — while white matter is composed of axons, which create a network of fibers that interconnect neurons. White matter gets its name from the white, fatty myelin sheath that surrounds the axons and speeds the flow of electrical signals from cell to cell.How chronic stress creates these long-lasting changes in brain structure is a mystery that researchers are only now beginning to unravel.In a series of experiments, Daniela Kaufer, UC Berkeley associate professor of integrative biology, and her colleagues, including graduate students Sundari Chetty and Aaron Freidman, discovered that chronic stress generates more myelin-producing cells and fewer neurons than normal. This results in an excess of myelin — and thus, white matter — in some areas of the brain, which disrupts the delicate balance and timing of communication within the brain.”We studied only one part of the brain, the hippocampus, but our findings could provide insight into how white matter is changing in conditions such as schizophrenia, autism, depression, suicide, ADHD and PTSD,” she said.The hippocampus regulates memory and emotions, and plays a role in various emotional disorders.Kaufer and her colleagues published their findings in the Feb. 11 issue of the journal Molecular Psychiatry.Does stress affect brain connectivity?Kaufer’s findings suggest a mechanism that may explain some changes in brain connectivity in people with PTSD, for example. One can imagine, she said, that PTSD patients could develop a stronger connectivity between the hippocampus and the amygdala — the seat of the brain’s fight or flight response — and lower than normal connectivity between the hippocampus and prefrontal cortex, which moderates our responses.”You can imagine that if your amygdala and hippocampus are better connected, that could mean that your fear responses are much quicker, which is something you see in stress survivors,” she said. “On the other hand, if your connections are not so good to the prefrontal cortex, your ability to shut down responses is impaired. So, when you are in a stressful situation, the inhibitory pathways from the prefrontal cortex telling you not to get stressed don’t work as well as the amygdala shouting to the hippocampus, ‘This is terrible!’ You have a much bigger response than you should.”She is involved in a study to test this hypothesis in PTSD patients, and continues to study brain changes in rodents subjected to chronic stress or to adverse environments in early life.Stress tweaks stem cellsKaufer’s lab, which conducts research on the molecular and cellular effects of acute and chronic stress, focused in this study on neural stem cells in the hippocampus of the brains of adult rats. These stem cells were previously thought to mature only into neurons or a type of glial cell called an astrocyte. The researchers found, however, that chronic stress also made stem cells in the hippocampus mature into another type of glial cell called an oligodendrocyte, which produces the myelin that sheaths nerve cells.The finding, which they demonstrated in rats and cultured rat brain cells, suggests a key role for oligodendrocytes in long-term and perhaps permanent changes in the brain that could set the stage for later mental problems. …


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