[header] How to keep an older dog mentally active [title] Make sure your dog gets lots of interaction. [step] Dogs that are left alone all the time will not be able to stay mentally healthy. A dog that does not have a lot of social interaction can lose its mental acuity because it doesn't exercise its brain. 
Dogs are meant to have social interaction, as they are pack animals, and they need it to avoid becoming sad, lonely, and destructive. [substeps] Interaction can come in a lot of forms.