Last Week's Biggest Movers on Wall Street

Plenty of stocks go up and down in any given week. The gainers inspire us to keep investing. The decliners keep greed in check while reminding us about the risks of the equity markets.

Let's go over some of last week's best and worst performers.

Intra-Cellular Therapies (ITCI) -- Up 117 percent last week

The market's biggest gainer last week was once again a biotech company. Intra-Cellular Therapies saw its stock more than double after positive test results in the late-stage clinical trials for a promising schizophrenia drug.

Intra-Cellular's treatment proved effective only with the highest dose, but that only means that it will make that much more money if the drug that tackles schizophrenia symptoms clears regulatory hurdles.

Fitbit (FIT) -- Up 26 percent last week

Shares of the maker of fitness trackers got an excellent workout after Target (TGT) announced that it would make Fitbit bracelets available to its employees for free. This is a pretty big deal and not just because there are roughly 335,000 employees on the cheap-chic discounter's rolls.

Corporate wellness is an important perk these days, and if Target's buying its employees Fitbit, it could behoove other retailers to follow suit. Fitbit offers a cost-effective way to measure movement, encouraging wearers to lead more active lifestyles.

Yandex (YNDX) -- Up 11 percent last week

Russia's leading search engine got a double dose of good news. The first boost came in the form of Google (GOOG, GOOGL) being found guilty in a Russian antitrust probe having to do with the way the dot-com darling bundles apps in Android mobile software.

The other boost came in the form of a Goldman Sachs (GS) upgrade. Yandex has been hit with weak ruble concerns and Russia's volatility, but Goldman Sachs feels that the stock is undervalued despite the challenges.

Raptor Pharmaceuticals (RPTP) -- Down 42 percent last week

%VIRTUAL-WSSCourseInline-799%There's no denying that upstart biotechnology companies make up the market's most volatile industry. We saw that this week as Intra-Cellular was the market's biggest winner, and we are seeing that again with Raptor Pharmaceuticals as its biggest loser. The stock took a big hit after coming up short in a mid-stage clinical trial for what once was a potentially promising treatment for pediatric fatty liver. It failed to meet its primary endpoint, which basically means that it's not an effective treatment.

La Quinta (LQ) -- Down 14 percent last week

Investors checked out of La Quinta after a couple of problematic developments. The hotel chain lowered its guidance, and that's never going to please Mr. Market. La Quinta also announced that its CEO would be resigning, rocking investors who prefer stability at the top. Its CFO will be taking the helm.

Wall Street didn't take kindly to the news. At least two major firms -- Citigroup (C) and JPMorgan (JPM) -- downgraded the stock on the double dose of unwelcome news.

Sonic (SONC) -- Down 11 percent last week

Finally, we have the leading chain of drive-in restaurants shifting in reverse after a poorly received sales update. The company behind the chain of more than 3,500 Sonic fast-food restaurants offered up a tantalizing headline in a press release last week, boasting about the 7.3 percent spike in comps it achieved during the fiscal year that ended in August. However, dig a few sentences into the release, and you will find that comparable-restaurant sales only grew at a 4.9 percent clip during the final quarter.

It gets worse. Sonic initiated guidance suggesting that comps will climb 2 to 4 percent in the new fiscal year that began this month. Yes, the restaurant-level sales are still positive, but we're looking at decelerating growth. The market was clearly holding out for something better.

Motley Fool contributor Rick Munarriz has no position in any stocks mentioned. The Motley Fool owns and recommends Google (A and C shares). The Motley Fool recommends Yandex. Try any of our Foolish newsletter services free for 30 days. Check out our free report on one great stock to buy for 2015 and beyond.