Share-based compensation is accounted for in accordance with the provisions of ASC 718, Compensation-Stock Compensation.

The Company has granted stock option awards to employees, directors and consultants from its 2011 Stock Incentive Plan (the “2011 Plan”) and its 2016 Equity Incentive Plan (the “2016 Plan”). The estimated fair value of options granted is determined as of the date of grant using the Black-Scholes option pricing model. The resulting fair value is recognized ratably over the requisite service period, which is generally the vesting period of the awards.

Share-based compensation expense for options granted under the 2011 Plan and the 2016 Plan is reflected in the statements of operations as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Research and development	$	290	$	243	$	881	$	1,066
General and administrative		384		543		1,176		2,166
Total	$	674	$	786	$	2,057	$	3,232

The following table summarizes the activity related to stock options during the nine months ended September 30, 2020:

				Weighted
	Number of			Average
	Shares			Exercise Price
Options outstanding at December 31, 2019		4,104,450		$	4.63
Granted		1,100,250			2.31
Exercised		(253,216	)		0.89
Forfeited		(702,041	)		6.49
Options outstanding at September 30, 2020		4,249,443			3.95

Options exercisable at December 31, 2019		2,452,764			5.44

Options exercisable at September 30, 2020		2,225,536			4.97

As of September 30, 2020, the Company had $4.1 million of unrecognized compensation expense related to unvested stock options, which is expected to be recognized over a weighted average period of 2.3 years.

The Company has granted restricted stock units (“RSUs”) to employees from the 2016 Plan. The shares underlying the RSU awards have vesting terms of one to four years from the date of grant subject to the employees’ continuous service and subject to accelerated vesting in specified circumstances.

The fair value of the RSUs granted is measured based on the market value of the Company’s common stock on the date of grant and is recognized ratably over the requisite service period, which is generally the vesting period of the awards.

The following table summarizes the activity related to RSUs during the nine months ended September 30, 2020:

				Weighted Average
	Number of			Grant Date
	Shares			Fair Value
Non-vested RSUs outstanding at December 31, 2019		1,269,300		$	0.87
Granted		486,000			2.39
Vested		(887,575	)		0.93
Forfeited		(6,700	)		0.91
Non-vested RSUs outstanding at September 30, 2020		861,025			1.67

The Company recorded $0.2 million and $45,000 of share-based compensation expense for the three months ended September 30, 2020 and 2019, respectively, and $0.7 million and $0.2 million for the nine months ended September 30, 2020 and 2019, respectively, for the RSUs. As of September 30, 2020, the Company had $1.2 million of unrecognized compensation expense related to the RSUs, which is expected to be recognized over a weighted average period of 2.6 years.

The 2016 Employee Stock Purchase Plan (the “2016 ESPP”) became effective on June 1, 2016. The 2016 ESPP is considered a compensatory plan and the fair value of the discount and the look-back period are estimated using the Black-Scholes option pricing model and expense is recognized over the six-month withholding period prior to the purchase date. The Company recorded $17,000 and $2,000 of share-based compensation expense for the three months ended September 30, 2020 and 2019, respectively, and $24,000 and $15,000 for the nine months ended September 30, 2020 and 2019, respectively, in the statements of operations for the estimated number of shares to be purchased on the next purchase date following the conclusion of the applicable reporting period. During the nine months ended September 30, 2020, the Company issued 35,359 shares of common stock purchased under the 2016 ESPP.