Over the past week, Artie has been speaking so rapidly that people have a hard time keeping up with what he says. He changes topics mid-sentence, and although much of what he says is understandable, his accelerated, disjointed speech and idiosyncratic phrases make it difficult to follow his train of thought. This recent change is especially noticeable, since Artie had been struggling with depression three months earlier. What is the most likely diagnosis for Artie?