This is a root that has been used for centuries in Ayurvedic medicine. It is used as a tonic to reduce stress and anxiety. There is some research to support compounds found in Ashwagandha improve memory in normal mice and those with dementia. I am always curious as to how you determine if a mouse has dementia? Ashwagandaha is also considered to be a potent antioxidant.
Bacopa is also used in Ayurvedic medicine to strengthen the nervous system. Recent awareness has stimulated it used as a brain tonic and memory enhancing herb. It is considered of value in enhancing memory and retention and is also an antioxidant. 
Ginkgo is one of the oldest species and has had a reputation for improving memory and brain funciton. It is probably one of the most popular of all the memory enhancing herbs. Laboratory studies have indicated that Ginkgo extracts promote nerve cell growth and inihibit damage to nerve cells. Gingko can help delay mental deterioration in the early stages of Alzheimer’s disease and other demential. Studies have been conducted and published by the American Medical Association that indicate if used three times daily noticeable improvement in cognitive function results.
Rosemary is used in traditional medicine to increase concentration and memory and also for relieving stress. Put a few drops of Rosemary oil in your diffuser to help reduce stress and improve relaxation. Try this and see if it improves your memory or your mood.