Stocks were holding onto earlier gains in midday trading Monday as markets hovered in wait-and-see mode. Potential market movers on the horizon include Apple (AAPL) earnings after the bell and the beginning of the Federal Reserve's two-day meeting on Tuesday. Tesla (TSLA) was leading the Nasdaq ahead of a scheduled presentation on Thursday. The company is expected to diversify the uses of its lithium-ion batteries into the home energy market. Biotech company Celladon (CLDN) tanked after a trial of its heart failure treatment missed its primary and secondary endpoints. Google (GOOGL) shares moved slightly lower after the company announced an experimental program to purchase patents.