The anemia is likely to to flea bites. Get rid of the fleas by bathing (then dry since kittens can become very cold) and combing. Obtain Frontline spray for flea control which can be used by administering 1 spray per 1 pound body weight but is usually recommended for kittens that are 6-8 weeks old. For younger, tiny kittens, I will typically pump one spray onto a cotton ball and then gently dab the cotton ball on the kitten if the flea burden is severe. Monitoring the kitten's gums was a great idea (normal gums are pink/moist). Since your kitten's gums are pink, it likely will not require a blood transfusion but as stated before, flea bites in a small kitten can be fatal and can occur fairly quickly.
As far as the "brain damage" occurs, the kitten may have contracted a disease called feline panleukapenia which can cause cerebellar hypoplasia (underdevelopment of the cerebellum) manifested by incoordination (ataxia) in kittens beginning at two to three weeks of age. Panleukopenia normally has a high mortality rate, but with good supportive care this can often be reduced. The main objective is to keep the affected animal alive and in reasonably good health until the kitten is able to develop antibodies to this disease (usually appear 3 to 4 days after intial infection). If the kitten survives, it still may develop other secondary infections as a result of this virus. I would advise you to have a veterinarian evaluate this kitten so that they can give you a better long term prognosis. Best of luck and I hope the kitten is doing better.