I was in the same position as you.. psych major, TBI lab research assistant, even a super-senior. It can be tough to get into a lab that will only take you for one year, especially in another department. I suggest starting by looking within your department, even within your current lab. Sometimes there are really interesting projects going on around you that you may not know about until you ask. In my case, I ended up going from coding neuropsychological assessments (yawn...) to working on a longitudinal TBI study looking for structural and functional MRI changes. It ended up bringing me closer to the more basic sciences - in this case, MRI physics and mathematics (computer programming). If you're looking to really get your hands dirty in something like biology or chemistry labs, you might try to score a position in a lab in another department. If I were you, I might even offer to start in the summer to sweeten the deal for the PI.