you can do this by going to Admin>SFDC>sync activities
not recommended due to overhead.
Yes, it is possible to include the Sales Insights data into the activity history. I would definitely recommend being intentional with what you have populated in the activity history from Sales Insights. You do not want to create a lot of clutter that would prevent sales from effectively using the activity history nor exceed your SF data allocation.
I have seen one case where a client had synced EVERYTHING from Sales Insights to the activity history and were broaching the upper limits of their agreement w/ SF. Each business has a different set of requirements and preferences but I typically recommend only including communication sends (text or email) and key activities (content download, event registration ectc.).
Hope this helps.