This week I came across a brain stimulation device called Humm that promises to improve your cognitive function and memory if you stick it to your forehead.

The Humm device. Image adapted from https://thinkhumm.com/preorder

There are several broadly similar devices on the market, which make use of the principle of transcranial alternating current stimulation (tACS) – passing a current through the head (the front of the head, generally) in order to modulate brain activity.

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