Adding information about a study demonstrating the overlap in brain areas for understanding stories and social interactions best supports the writer's argument about the benefits of reading on brain function.
To best support the writer’s argument in the third paragraph, the piece of evidence that should be added would be information about a study that showed substantial overlap in the parts of the brain used to understand stories and those used to navigate interactions with other people.
This evidence is directly relevant to the discussion of the benefits of literature on brain activity and would provide scientific backing to the writer's claims regarding brain function.
The paragraph is concerned with the impact of reading and literature on the brain; therefore, empirical research such as findings from a neurological study would serve as strong support for the writer's argument.