Your ability to understand & 'feel' an emotion is affected by your physical expression of that feeling. In simple terms, this is why it's hard to feel angry if you're laughing. In this study, 40 women were tested on their ability to assess the emotion in a written sentence after having 'frown line' Botox. After the injection, the women were slower to understand sadness and anger. It seems that Botox makes you less capable of responding to an angry or upset person. The report says: Let's say that, in a marital disagreement, your spouse is repeatedly just a tenth of a second too slow in responding, leaving the mounting impression of disinterest or failure to comprehend.
So if you've had Botox and DP says you don't seem to understand him, he could be right!
It was only a small study, but it does fit what we know about 'somatic response'. It's also made me wonder about Asperger's - if AS people are taught to use appropriate facial expressions in conversation, does it help their interactions? Or is that bit of mental wiring completely absent in ASDs?