By definition, a TIA should cause symptoms that last no more than 24 hours. If your mother is still having symptoms from an event that took place last year, this would be considered a stroke, not a TIA. That said, with regards to vascular dementia, a TIA can cause damage to the brain that is not noticeable to the patient but can be seen on radiologic imaging. Much like waves wearing down a stone on a seashore, an individual wave may cause no noticeable damage, but over time erosion can occur. Therefore, if your mother is suffering from vascular dementia, she should be evaluated for stroke and TIA risk factors such as high blood pressure, diabetes, high cholesterol, smoking, and diet. These risk factors should be aggressively controlled for the safety of her cognitive health. Limiting the number of TIAs and small strokes she suffers will slow down the progression of your mother's illness.