My current rehab patient Mr. P. had a stroke during bypass surgery following a heart attack. The stroke affected him in the following way: he has agraphia making it difficult for him to write, alexia which is affecting his reading and acalculia.
Acalculia is the loss of the ability to perform mathematical operations (even simple ones). When I first started working with Mr. P. he could not count from 1 to 20 (forwards and backwards) without making several mistakes, he could not write numbers, he could not calculate at all. Additionally, his attention span was really low, and he had memory problems.
After three weeks of neuro rehab geared towards his acalculia and memory problems, Mr. P. is now able to do additions and subtractions up to 100. He can also do simple multiplications. He is able to write numbers and has a better grasp of them too. His memory has gotten better and he's able to focus on therapy.
Imagine being 70 years old, and having to learn something that you learnt in elementary school all over again, working hard to do calculations that your grandchildren can do without even having to think about it.
Nevertheless, he has worked really, really hard in therapy, and I am so proud of him.