Inner Cosmos's 'digital pill'  comprises an electrode that sits under the skin of the scalp and the 'prescription pod' that snaps onto the users' hair to power the device.

The implant sends tiny electrical pulses to the brain region affected by depression - the left dorsolateral prefrontal cortex - once daily for 15 minutes.

And the external device does not need to be on the head when treatment is not being administered.

The hairy trial patient from St Louise, Missouri, is scheduled to test Inner Cosmos innovation for one year, and the company has another human trial set to start next month.

The implant is about the size of a penny and surgery for the implant takes 30 minutes in an outpatient facility.

Inner Cosmos was founded by entrepreneur Meron Gribetz, who was diagnosed with attention deficit disorder as a child.

"Our mission is to create a world that restores humanity's cognitive power by rebalancing the human mind. The world is in a state of severe disorder, leading to a disordered cognition. 'The effects are being felt by millions, leading to surging levels of depression. We believe our approach can allay the lives of those suffering from depression, and eventually scale to other cognitive disorders," he said.