In an effort to overcome this drawback, the Tuszynski research team has recently conducted a study of ex vivo gene therapy with nerve growth factor. Similarly, in clinical trials where human nerve growth factor gene were grafted into the fibroblasts harvested from each patient and that were transplanted back into the basal forebrain area  of the patient, 6 patients were confirmed to show improvements of cognitive functions and increases of cerebral cortex metabolism in positron emission tomography after 22 months of the intervention without any side effects or toxicity, with 2 of them showing improvements in cognitive performances, electroencephalography, and nicotinic receptor binding.