Friday added to Thursday's big gain, as more brokers upgraded the stock after federal regulators unexpectedly approved its treatment for depression.

The stock rose 62 cents, or 1.6%, to $39.63, near a 52-week high, after surging 42% Thursday in trading volume 28 times the daily average.

Sun Trust Robinson Humphrey and AG Edwards were the latest brokers to upgrade the stock.

The Food and Drug Administration of Wednesday reversed an earlier decision and gave conditional approval to Cyberonics' VNS Therapy system for treating depression. The pacemakerlike device, which is surgically implanted into a patient and delivers mild electrical shocks to a nerve in the brain, has been available in the U.S. since 1997 as a treatment for epilepsy.

The decision is a major victory as well as a reversal of fortune for Cyberonics, whose shares swooned last summer when the FDA rejected the treatment, which already had been endorsed by an advisory panel -- an extremely rare occurrence.

Cyberonics reports quarterly earnings Feb. 8.