There are several Ginkgo Biloba Liquid Extracts available. The following link is for Puritan's Pride's Ginkgo Biloba Extract. Please view the following link:
http://www.puritan.com/ginkgo-biloba-052/ginkgo-biloba-liquid-extract-007812?afid=27&safid=Google&scid=6835&cm_mmc=Google-_-Herb_Ginkgo-_-liquid%20ginkgo%20biloba-_-Broad+Ad_2456579731%7C-%7C100000000000000041868&cm_guid=1-_-100000000000000041868-_-2456579731&gclid=CL6jx-q4kJ0CFQtN5QodPw6p1w
There are many other choices for Liquid Ginkgo Biloba Extract (google it), just make sure they only contain glycerin and not alcohol. Cats dislike the taste of alcohol, and it is contraindicated in a cat susceptible to pancreatitis.
The dose would be 1/8 dropperful twice to three times daily. Please start with a very low dose and gradually increase over a week's time. As with most holistic preparations it takes 2 to 3 weeks to see effects. The side effect of this herb is thinning of the blood, but should be safe at the low dose I have listed. To be totally safe, a CBC can be performed after your cat has been on Ginkgo for 2 to 3 weeks, if necessary.
Phosphatidyl Serine, and/or Choline, DHA, and Omega 3 Fatty Acids may also be helpful. Use approximately 1/10 human dose.