I love brains and I have had two so far. I experimented with the first one too much, then it died. so my new brain is doing fantastic.
I did learn the following so hopefully this insight helps.
When I turn off my lunar lights at night, it takes just about 10 minutes for the brain to start opening up and releasing its tentacles. At this point it allows you to spot feed it more efficiently. I do this three times a week, and I spray it with cyclopeeze, along with my home made food (Clams, squid, shrimp,) and allow some small but big enough chunks of food to rest on top of it. I started being extra cautious that my hermits or shrimps did not go over and steal the food. Now I just do it and forget about it.
So the key here was that I turned off the lights to allow to look for food, then I fed it.
If it does not react to your lights, it may be dying. Take it out for inspection.