Complex sentence: These theorists propose that the function of mirror neurons in social cognition is not so much to "mirror" the target's action; rather the function is to instantly prepare a complementary action in response to the target.
Split into simpler sentences: These theorists propose that the function of mirror neurons in social cognition is not so much to "mirror" the target's action. Rather, the function is to instantly prepare a complementary action in response to the target.