The Company has two equity incentive plans: The Amended and Restated 2013 Equity Incentive Plan, or the 2013 Plan, and the 2007 Equity Incentive Plan, or the 2007 Plan. The 2013 Plan includes a provision that shares available for grant under the Company’s 2007 plan become available for issuance under the 2013 Plan and are no longer available for issuance under the 2007 Plan.

At the Company’s annual meeting of stockholders held on July 16, 2021, the Company’s stockholders approved amendments to the 2013 Plan, which included an increase in the number of non-inducement shares of common stock authorized for issuance under the 2013 Plan by 1,300,000 shares. On February 14, 2022, and March 22, 2022, the board of directors approved an increase of 1,000,000 and 500,000 shares, respectively, in the inducement shares of common stock authorized for issuance under the 2013 Plan.

As of March 31, 2022, 2,263,088 shares of the Company’s common stock were authorized exclusively for the issuance of stock awards to employees who have not previously been an employee or director of the Company, except following a bona fide period of non-employment, as an inducement material to the individual’s entering employment with the Company, as defined under applicable Nasdaq Listing Rules.

As of March 31, 2022, under all plans, a total of 4,599,497 shares were authorized for issuance consisting of 2,336,409 non-inducement stock options and 2,263,088 inducement stock options. As of March 31, 2022, 1,858,427 non-inducement shares and 1,599,918 inducement shares had been issued and 667,663 non-inducement shares and 513,032 inducement shares were available for grant. Outstanding awards as of March 31, 2022, consisted of 1,603,596 non-inducement shares and 1,599,918 inducement shares.

A summary of stock option activity for the three months ended March 31, 2022 is as follows:

	Number of Shares			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term in Years
Outstanding at December 31, 2021		2,413,194		$	7.04		9.06
Granted		1,155,570		$	2.35
Cancelled/forfeited/expired		(365,250	)	$	6.44
Outstanding at March 31, 2022		3,203,514		$	5.50		7.80
Vested and unvested expected to vest, March 31, 2022		3,162,485		$	5.52		7.78

The intrinsic values of options outstanding, options exercisable, and options vested and unvested expected to vest at December 31, 2021 and March 31, 2022 were each $610 and $0, respectively.

The assumptions used in the Black-Scholes pricing model for stock options granted during the three months ended March 31, 2022 were as follows:

		2022
Stock and exercise prices		$2.32 - $2.39
Expected dividend yield		0.00%
Discount rate-bond equivalent yield		1.76% - 2.41%
Expected life (in years)		5.55 - 6.03
Expected volatility		161% - 163%

The fair value of restricted stock units, or RSUs, awarded under either plan is determined by the closing price of the Company’s common stock on the date of grant. For non-performance RSUs, such value is recognized as expense over the requisite service period, net of estimated forfeitures, using the straight-line method. The amount and timing of compensation expense recognized for RSUs is based on management’s estimate of the most likely outcome and when the achievement of the performance objectives is probable. There were no RSUs granted for the quarter ended March 31, 2022.

At March 31, 2022, the intrinsic values of RSUs outstanding and RSUs unvested and expected to vest were each approximately $84. Of the 36 RSUs outstanding, all were fully vested as of March 31, 2022.

The following table presents the effects of stock-based compensation related to equity awards to employees and nonemployees on the unaudited condensed statements of operations and comprehensive loss during the periods presented:

	For the Three Months Ended March 31,
	2021		2022
Stock Options
Cost of revenues	$	94	$	208
Research and development expenses		44		166
General and administrative expenses		260		1,802
Sales and marketing expenses		62		141
Total expenses related to stock options		460		2,317

As of March 31, 2022, total unrecognized share-based compensation expense related to unvested stock options and RSUs, adjusted for estimated forfeitures, was $6.5 million and is expected to be recognized over a weighted-average period of approximately 2.97 years.