"It took a while to piece together why I was even in an ambulance and why I didn't have teeth, " said Stevens, whose injuries resulted in 40 stitches to her face, dental implants and memory loss.

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As the rats did this memory task, electrodes in the implants recorded signals between two areas of their brains involved in storing new information in long-term memory.

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Technologies such as exoskeletons that provide increased strength and implants that improve memory will put both definitions under pressure.

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