"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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Human-enhancement researchers at the University of Reading, for their part, are considering future technologies, such as embedded devices that enhance the senses or add new ones, and implants that improve memory or allow messages to be sent or devices to be controlled using thought alone.

ECONOMIST: Monitor