Hi Gang,

Thanks for clarifications. That worked. I see that running this model gives me main effect of Load, chrom, AgeD and interactions between the three. This looks like what I want to move forward. I want to clarify further on the interpretation of the clusters of activation for effects that show an interactions with AgeD versus no interactions with AgeD.
Does this sound correct:
In an interaction between AgeD, load and chrom, clusters represent regions that show differences in activation between one or more levels of load and chrom that varies with Age. On the other hand, clusters from an interactions between load and chrom represents regions that show differences in activation between levels of load and chrom, but these differences do vary with Age (i.e. controlled for Age).