In modern medicine, the cause of a person's dementia typically cannot be determined until autopsy. thus, clinical research method continues to be of significance in medicine and psychology.

I believe the answer is: Broca's

He was the first to introduce deficit-lesion method, which examine lesion data in order to determine the brain areas that are involved when we are doing a certain type of cognition process.  Even until today, this method is regarded as the one of the most important invention for data collection in neuro science.