I’m choosing between these three to apply ED with a cognitive science major (possibly pre-med) in mind. I thought I was set on Swarthmore because I love everything about it, but I’m worried about the fact that their cognitive science special major is less structured and well-established (as far as I can tell, correct me if I’m wrong) than WashU or Brown. I love the open curriculum at Brown and the campus at WashU, but both are a little bigger than I’d like and I’m concerned that they wouldn’t have the same feeling of academic closeness found at a small liberal arts college like Swarthmore. I also plan to participate in research and expect that there would be many more opportunities for that at an undergrad-only institution. However, both Brown and WashU have many, many more specific majors that I’m interested in, such as genomics and computational bio. Any insight into any of the schools is appreciated!
Those are three excellent schools and I don’t think you’ll be limited, either in major choice or research opportunities, at any of them. I will say that in 1981 my RA at Swarthmore was an honors major in Bio-Psycho-Linguistics. There was no such major listed in the catalog, it was a triple major created by her to follow her own specific interests. If you’re passionate about something and willing to work I think you can find a way to pursue it, at Swarthmore or Brown or WashU. I would make the decision based upon your chances of getting accepted (why waste your ED), the location, size, environment and cohort. College is about more than what you study in your major classes - it’s also who you study with, how you broaden your mind with new topics and also what you do when your brain is full up with studying! 
Good luck! I hope you get into your ED school, whatever the choice!
@CaMom13 I was with you until this statement
I don’t think that is a good reason to pick a school ED.
@Eeyore123 if a student is torn between 3 excellent schools and one is a far reach for their stats and another is a match or near reach I would recommend the student choose the school at which they are more likely to be accepted. ED gives an applicant an edge in acceptances but students accepted ED aren’t any less qualified than the kids accepted RD so it’s not like a reach becomes a match if you ED. imo choosing a far reach to apply ED is a wasted opportunity if you have other schools you like just as much at which you have a better chance of admission.
If you love everything about Swarthmore…there’s your answer.
except that Swat doesn’t exactly have the majors of interest. OP appears to prefer the LAC size, but is seeking the academic breadth of a larger Uni. Only OP can decide which is more important.
Personally, I’d rec the OP consider Amherst – open curriculum and the first neuroscience program offered by a LAC. Other stuff of interest could be had as an elective at UMass.
I couldn’t agree more with @Eeyore123. Use ED to go where you want to go. You could never determine where you have the best chance for ED admission between the 3 schools listed.
My eldest graduated Swat in 2018, and I can tell you that a lot of her friends spent summers doing research on / around campus. She did research one summer for a professor at Swat, and then the next at a Drexel Lab for a Swat alum (with a scholarship from Swat… it was free to Drexel / the alum). It feels like there are plenty of summer opportunities through school. Swat also has a fairly robust Externship program it runs in January. Students spend one week with an alum, experiencing their day to day and occasionally doing a bit of work. She did 2 of those and really enjoyed them.
Several other LACs offer a notably flexible curriculum and a neuroscience major (e.g., Hamilton, Smith, Grinnell). However, for the oldest cognitive science major in the world, look into Vassar.