6. Stock Based Awards

Equity Incentive Plans

The Company adopted an equity incentive plan in 2007 (the “2007 Plan”) under which 1,786,635 shares of common stock had been reserved for issuance to employees and nonemployee directors and consultants of the Company. The Company no longer issues any awards under the 2007 Plan. Holders of outstanding incentive stock options granted under the 2007 Plan are eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the fair market value of such stock on the date of grant. The maximum term of options granted under the 2007 Plan was ten years.

The Company adopted a second equity incentive plan in 2015 (the “2015 Plan”) under which 2,705,237 (including 1,038,570 initially transferred from the 2007 Plan) shares of common stock have been reserved for issuance to employees, and nonemployee directors and consultants of the Company. Recipients of incentive stock options granted under the 2015 Plan shall be eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair market value of such stock on the date of grant. The maximum term of options granted under the 2015 Plan is ten years. As of March 31, 2020, 3,595,643 options remain available for future grants under the 2015 Plan.

The following table summarizes stock option transactions for the 2007 Plan and 2015 Plan, collectively, for the three months ended March 31, 2020 and 2019 (in thousands, except per share amounts):

The Company did not grant any options during the three months ended March 31, 2020, nor the three months ended March 31, 2019.

The Company accounts for share-based awards to employees and nonemployees directors and consultants in accordance with the provisions of ASC 718, Compensation—Stock Compensation., and under the recently issued guidance following FASB’s pronouncement, ASU 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. Under ASC 718, and applicable updates adopted, share-based awards are valued at fair value on the date of grant and that fair value is recognized over the requisite service, or vesting, period. The Company values its equity awards using the Black-Scholes option pricing model, and accounts for forfeitures when they occur. For the three months ended March 31, 2020 and 2019, equity-based compensation expense recorded was $107,000 and $33,000, respectively.

As of March 31, 2020, there was approximately $1,072,000 of total unrecognized compensation expense related to non-vested stock options that is expected to be recognized over a weighted average period of 1.4 years. For options granted and outstanding, there were 923,065 options outstanding which were fully vested or expected to vest, with an aggregate intrinsic value of $0, a weighted average exercise price of $4.15, and weighted average remaining contractual term of 7.84 years at March 31, 2020. For vested and exercisable options, outstanding shares totaled 413,690, with an aggregate intrinsic value of $0. These options had a weighted average exercise price of $5.84 per share and a weighted-average remaining contractual term of 7.1 years at March 31, 2020.

The aggregate intrinsic value of outstanding and exercisable options at March 31, 2020 was calculated based on the closing price of the Company’s common stock as reported on The Nasdaq Capital Market on March 31, 2020 of $0.71 per share less the exercise price of the options. The aggregate intrinsic value is calculated based on the positive difference between the closing fair market value of the Company’s common stock and the exercise price of the underlying options.

Common Stock Reserved for Future Issuance

The following table presents information concerning common stock available for future issuance (in thousands) as of: