Can I still get involved in psychology/neuroscience with a computer science degree from several years ago? In the three years since getting my B.S. in Computer Science I have become more interested in biology again (my original major) and also in psychology and neuroscience. My current job -- which is more Information Technology than actual Computer Science -- is not fulfilling. My level of interest when learning about the brain and/or mind is so much higher than, say, learning about the architecture of some web application. 


Is moving into psychology and/or neuroscience as drastic of a switch as I think it is? Does anyone have any advice for how best to start down that path?
If I decide to do this, I am assuming some graduate school will be required. Given that I finished undergrad with just average grades, is it a fool's errand to even consider going down this road?
I don't think it's foolish.

If you want to make the switch, I'd look into BS-requiring lab tech jobs in labs doing things you are interested in, and trying to apply for graduate school in a year or two if that works out well.

These are jobs that recently-graduated students often do for a year or two while strengthening an application for graduate school, and in my experience a CS background can be quite useful to many labs. The lab I work in often takes on undergraduate assistants in CS, and some of those students choose to keep working after graduating (or come from elsewhere after graduating).

Titles for these jobs vary a lot by institution, but I've seen "research intern", "junior scientist", "research technician", etc. You can both look at job postings and try to contact professors directly; know that both methods may have a high rejection rate. You'll have the best chance if you both a) learn enough about what particular labs are doing to be able to describe why working there would interest you, and b) don't paint yourself into such a narrow focus that many opportunities are ruled out. Don't be afraid to contact past professors even if you've been out of school for a bit and ask their advice.

Expect to take a pay cut compared to your industry job, and to not have much (any) negotiating power. The things you would want to stress when you apply are that you are interested in making a career move to academia and pursuing a graduate degree, but want to get research experience. Look for jobs where you'll have an opportunity to work on projects and publish rather than becoming de facto IT support.

Poor undergraduate grades will hurt you - grad school applications can be very competitive, especially at better known schools (but don't discount other research institutions; good mentors are more important than Ivy-tier names). Your goal would be to accrue research experience and solid letters of recommendation: these can compensate a lot for average grades. At the same time, you should make it a personal goal to learn more about the specific fields of research and research questions you might be interested in, even if they're outside the work you start doing initially.

I'm speaking from a US perspective, so if you are elsewhere things may be a bit different. Good luck.