Jack, our English cocker spaniel, is eight years old, middle-aged for a dog. He may be a little neurotic, after all he is a spaniel, but he is still sharp as a tack and has no signs yet of cognitive impairment. It turns out that many mammals do develop cognitive impairment toward the end of their lives. In dogs, this cognitive decline is called canine cognitive dysfunction (CCD), and it occurs in up to 60% of dogs over 11 years of age. It is more common in small dogs probably because they tend to live longer than large dogs. As we shall see, it has similarities, and some differences, compared to Alzheimer’s disease in humans.