If the rise in risk aversion pushes down long-term yields on risk-free government bonds, how do central banks react?

The sharp rise in risk aversion in financial markets since the summer of 2018 has led to a significant decline in long-term yields on risk-free government bonds (United States, core euro-zone countries). How are central banks reacting to this situation? By combating the fall in long-term interest rates via a more restrictive monetary policy? By validating the fall in long-term interest rates and moving in step with it via a more expansionary monetary policy, in response to the overall deterioration in the economy and markets which may result from rising risk aversion, and to prevent an inversion of the yield curve? In the past, when risk aversion brought down long-term interest rates , central banks also cut their key interest rates.