What evidence? Asbsolutely libraries full. You can start with the review articles from Berridge Lab, https://sites.lsa.umich.edu/berridge-lab/publications/ http

What evidence? Asbsolutely libraries full. You can start with the review articles from Berridge Lab, https://sites.lsa.umich.edu/berridge-lab/publications/ https://sites.lsa.umich.edu/berridge-lab/publications/ . http://sites.lsa.umich.edu/berridge-lab/wp-content/uploads/sites/743/2021/06/2021-Nguyen-Naffziger-Berridge-Positive-affect-Cur-Opin-Behav-Sci.pdf http://sites.lsa.umich.edu/berridge-lab/wp-content/uploads/s... is a good overview article.