May 1 (Reuters) - Neurotrope Inc said on Monday its experimental drug improved cognition levels in a small mid-stage study in patients with Alzheimer's, a memory-robbing disease that has long confounded scientists.

The drug, Bryostatin-1, induces the growth of synapses in the brain and prevents cell death and is aimed at stopping the formation of a toxic amyloid protein that turns into plaques in the brains of Alzheimer's patients.

Existing treatments only soothe symptoms, and drug developers have suffered crushing disappointments in their efforts to find an effective way to reverse cognitive decline that affects more than 5 million Americans.

Researchers are now increasingly focusing on attacking the disease before symptoms have taken hold.

In the Neurotrope trial, two doses of Bryostatin-1 were tested against a placebo, in addition to the standard treatment in 147 patients with moderate-to-severe disease. A total of 113 patients completed the study.

Among those, 80 patients on the smaller 20 milligram dose of the drug achieved a statistically significant improvement in cognition in severe dementia patients, the company said on Monday.

However, in about 90 patients who received the drug but did not complete the study, Bryostatin-1 did not bring about a statistically significant improvement. (Reporting by Natalie Grover in Bengaluru; Editing by Saumyadeb Chakrabarty)