Repeated Measures ANOVA or Linear Mixed Model


I am looking to clarify which statistical test to use for my research, as I know that generally the simpler the test the better. I am looking at EEG amplitude in patients who completed the same neurofeedback protocol over 40 sessions. I am comparing two groups, one of treatment responders and the other of non-responders. I want to compare the groups and see if the amplitudes of the responders decreased linearly more over time compared to the non-responders. Due to the use of repeated measures (EEG amplitudes recorded at each of the 40 sessions), would it be better to apply a linear mixed model to compare the two groups in amplitude changes or a repeated measures ANOVA? I know they are somewhat related (with LMM being more complex and difficult) but figure that the LMM might be more appropriate considering the length of time (40 sessions). There is no missing data but am not sure whether to treat session number as continuous or categorical. Any guidance would be much appreciated.

Tristan Sguigna