Correct term or phrase for "unidirectional gaga"

Question

I'm not sure if such a figure of speech exists in English, and "unidirectional gaga" is certainly not correct.

But which wording expresses that a person becomes dumber from having exercised/performed something too frequently or in only one particular fashion.

• It's an adverb or phrase that is usually applied to a person. But can also describe activities.
• It primarily expresses "to make stupid" caused by a particular behaviour/performance.
• The persistence or repetetion of past activites is implied to turn the person more dull / less open to alternative approaches.
• Does usually but not necessarily have a derogatory meaning.

Possible alternative ways to express this:

• to become stultified

  • from ingrained habits
  • through monotony

• somebodys behaviour became dull

  • from tedious repetetion
  • ever the same approach

But of course I'm searching for a more catchy phrase or expression which coveres that sentiment.

Answer 1

As for forming a term from it's requirements:

Repititional dumbening?

Answer 2

What about recursively dumber?