Recent research suggests that repeated electromagnetic stimulation via a coil placed at the scalp, has been shown to in the treatment in of depression.

I believe the correct answer is transcranial magnetic stimulation (TMS).
Its definition matches that which you have given us above, as it includes the use of a magnetic field generator, referred to as 'coil,' in order to stimulate certain parts of the brain. The technique is used to treat various types of movement and mental disorders, including depression.

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

producing or giving rise torelating to or engaged in the production of goods, crops, or other commodities.

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.

This would be a true statement