Complex sentence: Specifically, frowns that incorporate the furrowing of the brow are a response to perceived obstacles to the achievement of goals, while frowns that involve movement of the cheeks reflect an unpleasant reaction.
Split into simpler sentences: Specifically, frowns that incorporate the furrowing of the brow are a response to perceived obstacles to the achievement of goals. While frowns that involve movement of the cheeks reflect an unpleasant reaction.