Being hit in the head with a blunt object, or accelerating too fast (in a rocket) can cause serious brain injuries for people.
There are animals who seem to fare better, like woodpeckers. Apparently, they have some soft tissue and neck muscles adapted to cushion the impacts. Also rams seem to have a bone structure adapted to minimize the brain damage from impact.
But, these animals also have smaller brains than people. I think their adaptation won't be good enough to guarantee brain safety against most impacts and sudden accelerations if their brains were our size.
What would be a good set of adaptations for people to be more resistant to concussions and sudden accelerations, that wouldn't make them look too different from us?