Bio Focus: Graphene microtransistors map brain activity
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BIO FOCUS
in CoCrFeNi contribute to its serrated stress–strain behavior and mechanical properties at low temperatures. According to Liaw, more in-depth analysis and modeling of this and other HEAs are needed to separate the contributions from deformation twinning and phase transition to the strength and ductility seen at the liquidhelium temperature. Such a study could
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be challenging because the two behaviors often appear simultaneously in some HEAs. Zhang hopes these results demonstrate the capabilities of HEAs at cryogenic temperatures, which could be used especially as materials for aerospace and nuclear-reactor applications. Lauren Borja
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Graphene microtransistors map brain activity
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he study of low-frequency brain signals, which is important for the diagnosis of many medical conditions, is limited by the microelectrode materials currently available. Now, researchers have shown that these infraslow brain waves, that is, brain activity that occurs at frequencies less than 0.1 Hz, can be monitored with high spatial resolution using graphene transistors. From the outside, the brain looks like a colony of neurons that communicate with each other in some sort of bizarre electrical language. Chemical conditions inside and around a neuron decide whether it will respond to or ignore an incoming signal from another neuron. If the conditions are right, a traveling electric potential is generated that moves across the brain. Most neural activity that has been studied so far is fast—greater than 1 Hz. However, infraslow activity (ISA) is becoming recognized for its involvement in a number of electrophysiological states such as sleep, coma, wakefulness, and anesthesia. Among these slow-moving brain murmurs are such ominously named entities as “spreading depolarizations” and “cortical spreading depressions” or CSDs. These slow-moving waves are often called brain tsunamis, which depolarize neurons and shut down large sections of the brain. CSDs are often triggered in cases of stroke or brain injury as well as during migraines and epileptic seizures. “In humans, terminal spreading depolarization (SD) has been measured within minutes following circulatory arrest and during the development of brain
b (a) Schematic of a flexible graphene solution-gated field-effect transistor (gSGFET) array technology; (b) microscope images of the active area of a 4 × 4 gSGFET array and a 15-channel intracortical array; and (c) photograph of the neural probe after peeling from the wafer and being introduced into a zero insertion force connector to interface with recording electronics. Credit: Nature Materials.
death. Transient SDs have been recorded in 90–100% of patients with severe stroke, 60–80% of patients with brain hemorrhage, and about 50% of patients with severe traumatic brain injury,” Jens P. Dreier of the Center for Stroke Research Berlin told MRS Bulletin. The study of these low-frequency brain signals are therefore important for diagnosis and cure in neurocritical care. In a recent issue of Nature Materials (doi:10.1038/s4
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