Nested experimental design of a drug screening using lmer in R I'm a bit stuck with the best formula to use in the lmer to analyze my data.
The effect on behavior (ALO) of different pharmacological treatments was tested in 2 different labs using rats. Each experiment was performed at least once, but some rats were tested 4 times for example.
The exp design looks more or less like this:

In R, I'm using lmer like this:
tS <- within(myTable, treatment <- relevel(treatment, 
             ref = "drug1")) #compare to saline
lmer <- lmer(ALO ~ treatment + (1|lab) + (1|lab:rats:sessions), 
             data=tS)`

being lab a factor with random effect, as well as rats. Sessions are nested into rats, and rats into lab.
Now
question 1: is the formula correctly written? does it show the hierarchy I want to establish?
question 2: is sessions a factor that should be included?

Assuming the sessions are independent and have no effect on each other, and that all the measurements are valid (your comment some rats had to be tested more than once because of technical problems with the electrophysiological recording seems to suggest these values might be suspect?) then:
Question 1: ALO ~ treatment + (1|lab/rats) (although your formulation also works, without session) if you want to vary the intercept among labs and among rats within labs,
Question 2: I would not include it, as it brings no new information.
