I'm appalled at the amount of bad advice here. 12 hours and 35 answers after the question was asked there is only one correct response [1], plus one that doesn't really offer advice but asks followup questions that might lead them to a correct response.
The person says in their first paragraph:
> I had a neuropsych evaluation which commented on my poor memory and inability to think.
This suggests that something might be going on that is more than the usual reasons a person might feel that they aren't good at thinking. The usual reasons include inadequate eduction, lack of practice, lack of motivation, and similar.
Almost all the answers are suggesting ways that would be appropriate if the problem was due to one of those usual reasons.
Those are unlikely to actually help much if the problem is medical. Worse, they could lead to the person wasting time trying them instead of dealing with the medical problem.