2. Stock Plans
The following table summarizes the stock-based compensation expense recorded for awards under the stock option plans for the three and nine month periods ended September 30, 2015 and 2014: | | | Three Months Ended
September 30, | | Nine Months Ended
September 30, | | | (in thousands, except per share amounts) | | 2015 | | 2014 | | 2015 | | 2014 | | | Research and development | | $ | 42 | | $ | 33 | | $ | 280 | | $ | 206 | | | General and administrative | | | 50 | | | 38 | | | 379 | | | 251 | | | Total stock-based compensation expenses | | $ | 92 | | $ | 71 | | $ | 659 | | $ | 457 | | No tax benefit was recognized related to stock-based compensation expense since we have incurred operating losses and we have established a full valuation allowance to offset all the potential tax benefits associated with our deferred tax assets. We use the Black-Scholes-Merton option-pricing model with the following assumptions to estimate the stock-based compensation expense for the three and nine month periods ended September 30, 2015 and 2014: | | | Three Months Ended
September 30, | | Nine Months Ended
September 30, | | | | | 2015 | | 2014 | | 2015 | | 2014 | | | Weighted-average risk-free interest rate | | | 1.7 | % | | 1.7 | % | | 1.8 | % | | 2.0 | % | | Expected dividend payments | | | — | | | — | | | — | | | — | | | Expected holding period (years) 1
| | | 4.5 | | | 4.2 | | | 6.4 | | | 6.5 | | | Weighted-average volatility factor 2
| | | 1.65 | | | 1.66 | | | 1.61 | | | 1.66 | | | Estimated forfeiture rates 3
| | | 30 | % | | 31 | % | | 30 | % | | 31 | % | | (1) | Expected holding periods are based on the simplified method provided in Staff Accounting Bulletin No. 107 for “plain vanilla options.” | | (2) | Weighted average volatility is based on the historical volatility of our common stock. | | (3) | Estimated forfeiture rates are based on historical data. | No options were granted during the three month periods ended September 30, 2015 and 2014. The following table summarizes option activity for the nine month period ended September 30, 2015: | (in thousands, except per share amounts) | | Options | | Weighted
Average
Exercise
Price | | Weighted
Average
Remaining
Option
Term | | Aggregate
Intrinsic
Value | | | Outstanding at January 1, 2015 | | | 1,204 | | $ | 6.75 | | | 5.14 | | $ | 1 | | | Granted | | | 250 | | | 3.30 | | | | | | | | | Exercised | | | — | | | — | | | | | | | | | Expired or cancelled | | | (20) | | | 13.27 | | | | | | | | | Forfeited | | | — | | | — | | | | | | | | | | | | | | | | | | | | | | | | Outstanding at September 30, 2015 | | | 1,434 | | $ | 6.06 | | | 5.34 | | $ | 202 | | | | | | | | | | | | | | | | | | Exercisable at September 30, 2015 | | | 1,311 | | $ | 6.32 | | | 4.96 | | $ | 111 | | No shares of restricted stock were awarded to employees, directors and consultants during the three month periods ended September 30, 2015 and 2014. The following table summarizes restricted stock activity for the nine month period ended September 30, 2015: | (in thousands, except per share amounts) | | Restricted
Stock | | Weighted
Average
Exercise
Price | | Weighted
Average
Remaining
Term | | Aggregate
Intrinsic
Value | | | Outstanding at January 1, 2015 | | | 65 | | $ | — | | | 9.12 | | $ | 166 | | | Granted | | | — | | | — | | | | | | | | | Released | | | (65) | | | — | | | | | | | | | Expired or cancelled | | | — | | | — | | | | | | | | | Forfeited | | | — | | | — | | | | | | | | | | | | | | | | | | | | | | | | Outstanding at September 30, 2015 | | | — | | $ | — | | | — | | $ | — | | | | | | | | | | | | | | | | | | Exercisable at September 30, 2015 | | | — | | $ | — | | | — | | $ | — | | As of September 30, 2015, there was approximately $142,000 of unrecognized compensation expense related to non-vested stock options and restricted stock. This expense is expected to be recognized over a weighted-average period of 0.5 years.
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