By the way, although the summary refers to the actor playing the psychiatrist as 'James Merrill', he is in fact Gary Merrill and it is shown correctly in the cast listing on IMDb.
The show begins at a remote outpost in Greenland. Harry Guardino plays a Major who has just had one of his men die in the line of duty. Following this, Guardino appears to be losing his mind and he's sent to see a psychiatrist (Merrill). Now here is one of those "Outer Limits" impossible plot twists--Merrill is using some experimental mind device to actually look inside Guardino's head. And, an earthquake hits at that moment and the minds of the guys are switched!! But the more serious problem is that the madman is REALLY mad--and he's out to kill everyone! Can the folks at the base recognize what has happened before it's too late? This is a pretty ordinary episode--neither good nor bad. While the idea is far-fetched, Guardino and Merrill both did good jobs and managed to make the ridiculous seem possible. Worth seeing if not brilliant--though the ending is, oddly, rather sweet in some ways. Look for movie/TV regulars Ivan Dixon, Sally Kellerman and James Sikking in the episode as well.
By the way, I wonder if any of this led to the final episode of the original "Star Trek" series. That's because in that one, there are LOTS of similarities. Kirk changes bodies with an insane woman--leading to some hilariously bad acting--and one of the most notoriously bad episodes of the series.