The Company has several share-based compensation plans under which stock options, RSAs, RSUs, and other share-based awards are available for grant to employees, officers, directors and consultants of the Company.

The following table summarizes share-based compensation expense by award type (in thousands):

The following table summarizes the share-based compensation expense reflected in the consolidated statements of operations (in thousands):

Restructuring expenses include modifications to share-based awards held by employees impacted by the various workforce reductions (Note 18).

In April 2019, in connection with the Separation, all outstanding share-based payment awards were modified in accordance with the equity conversion-related provisions of the employee matters agreement with Cyclerion. No share-based compensation expense was recognized in connection with these modifications. Additionally, modifications with respect to the Company’s ESPP were made due to the change in share price as a result of the Separation. As a result of the modification to the ESPP, the Company recorded approximately $0.3 million of share-based compensation expense for the year ended December 31, 2019.

In connection with certain other modifications of share-based payment awards for the years ended December 31, 2020 and 2019, the Company recognized an insignificant amount and approximately $3.0 million in share-based compensation expense, respectively.

As of December 31, 2020, the Company has the following active stock benefit plans pursuant to which awards are currently outstanding: the 2019 Equity Incentive Plan (the “2019 Equity Plan”), the Amended and Restated 2010 Employee Stock Purchase Plan (the “2010 Purchase Plan”) and the Amended and Restated 2010 Employee, Director, and Consultant Equity Incentive Plan (the “2010 Equity Plan”). At December 31, 2020, there were 14,357,176 shares available for future grant under the 2019 Equity Plan and the 2010 Purchase Plan.

During 2019, the Company’s stockholders approved the 2019 Equity Plan under which stock options, RSAs, RSUs, and other stock-based awards may be granted to employees, officers, directors, or consultants of the Company. Under the 2019 Equity Plan, 10,000,000 shares of Class A Common Stock were initially reserved for issuance. Awards that are returned to the 2010 Equity Plan as a result of their expiration, cancellation, termination or repurchase are automatically made available for issuance under the 2019 Equity Plan. Awards that expire, cancel, terminate, or are repurchased under the 2019 Equity Plan will no longer be available for future grant. As of December 31, 2020, 9,651,783 shares were available for future grant under the 2019 Equity Plan.

During 2010, the Company’s stockholders approved the 2010 Purchase Plan, which gives eligible employees the right to purchase shares of common stock at the lower of 85% of the fair market value on the first or last day of an offering period. Each offering period is six months. There were 400,000 shares of common stock initially reserved for issuance pursuant to the 2010 Purchase Plan. The number of shares available for future grant under the 2010 Purchase Plan may be increased on the first day of each fiscal year by an amount equal to the lesser of: (i) 1,000,000 shares, (ii) 1% of the Class A shares of common stock outstanding on the last day of the immediately preceding fiscal year, or (iii) such lesser number of shares as is determined by the board of directors. As of December 31, 2020, there were 4,705,393 shares available for future grant under the 2010 Purchase Plan.

The 2010 Equity Plan provided for the granting of stock options, RSAs, RSUs, and other share-based awards to employees, officers, directors, consultants, or advisors of the Company. At December 31, 2020, there were no shares available for future grant under the 2010 Equity Plan.

RSAs are granted to non-employee members of the board of directors under restricted stock agreements in accordance with the terms of the 2019 Equity Plan and the Company’s non-employee director compensation policy, effective May 2019. Annual restricted stock grants to each non-employee member of the board of directors vest ratably over the period of service from the grant date through the Company’s 2021 annual meeting of stockholders, provided the individual continues to serve on the Company’s board of directors through each vest date. Initial restricted stock grants to new non-employee members of the board of directors vest annually over a three-year period from the date of grant provided the individual continues to serve on the Company’s board of directors through each vest date.

A summary of restricted stock activity for the year ended December 31, 2020 is presented below:

The weighted-average grant date fair value per share of restricted stock awards granted during the years ended December 31, 2020, 2019, and 2018 was $10.16, $10.96, and $18.58, respectively. Amounts relating to restricted stock awards granted prior to the Separation have not been adjusted to reflect the effect of the Separation on the Company’s stock price.

RSUs granted under the Company’s equity plans represent the right to receive one share of the Company’s Class A Common Stock pursuant to the terms of the applicable award agreement. Shares of the Company’s Class A Common Stock are delivered to the employee upon vesting, subject to payment of applicable withholding taxes.

Time-based RSUs generally vest over a two-to-four-year period on the approximate anniversary of the date of grant until fully vested, provided the individual remains in continuous service with the Company through each vesting date. The fair value of all time-based RSUs is based on the market value of the Company's Class A Common Stock on the date of grant. Compensation expense, including the effect of estimated forfeitures, is recognized over the applicable service period.

A summary of time-based RSU activity for the year ended December 31, 2020 is as follows:

The weighted-average grant date fair value per share of time-based RSUs granted during the years ended December 31, 2020, 2019, and 2018 was $11.59, $12.11, and $15.63, respectively. Amounts relating to time-based RSUs granted prior to the Separation have not been adjusted to reflect the effect of the Separation on the Company’s stock price.

Performance-based RSUs (“PSUs”) were granted to certain executives in 2020. PSUs vest upon the achievement of specified performance criteria over a two to three-year performance period, generally subject to the executive remaining in continuous service with the Company through the applicable vesting dates. The performance criteria applicable to the PSUs were (i) gaining the U.S. FDA’s acceptance of one or more additional New Drug Applications through internal development or acquisition of development-stage or commercial-stage programs (“Pipeline PSUs”), (ii) achieving certain profitability metrics (“Profitability PSUs”) and (iii) realizing relative total shareholder return goals (the “Relative TSR PSUs”).

The fair value of Pipeline PSUs and Profitability PSUs is based on the market value of the Company's Class A Common Stock on the date of grant. The Relative TSR PSUs are valued using the Monte Carlo simulation method on the date of grant. The weighted average assumptions used to estimate the fair value of Relative TSR PSUs were as follows for the year ended December 31, 2020:

Stock options granted under the Company’s equity plans represent the right to purchase one share of the Company’s Class A Common Stock pursuant to the terms of the applicable award agreement. Shares of the Company's Class A Common Stock are delivered to the employee upon exercise, subject to payment of applicable withholding taxes.

As of April 2020, the Company no longer grants stock options. Stock options previously granted under the Company’s equity plans generally have a ten-year term and vest over a period of four years, provided the individual continues to serve at the Company through the vesting dates. Options granted under all equity plans are exercisable at a price per share not less than the fair market value of the underlying common stock on the date of grant. The estimated fair value of options, including the effect of estimated forfeitures, is recognized over the requisite service period, which is typically the vesting period of each option.

The weighted average assumptions used to estimate the fair value of the stock options using the Black-Scholes option-pricing model were as follows for the years ended December 31, 2020, 2019, and 2018:

Expected volatility is based on the historical volatility of the Company’s Class A Common Stock. The Company estimates the expected term using historical data. The risk-free interest rate used for each grant is based on a zero-coupon U.S. Treasury instrument with a remaining term similar to the expected term of the share-based award. The

Company has not paid and does not anticipate paying cash dividends on its shares of common stock in the foreseeable future; therefore, the expected dividend yield is assumed to be zero.

The weighted-average grant date fair value per share of options granted during the years ended December 31, 2020, 2019, and 2018 was $5.89, $6.10, and $6.81, respectively. Amounts relating to stock options granted prior to the Separation have not been adjusted to reflect the effect of the Separation on the Company’s stock price.

The Company historically granted to certain employees performance-based options to purchase shares of common stock. These options are subject to performance-based milestone vesting. During the years ended December 31, 2020 and 2019, there were no shares that vested as a result of performance milestone achievements. The Company recorded no share-based compensation expense related to these performance-based options during each of the years ended December 31, 2020, 2019, and 2018.

The following table summarizes stock option activity under the Company’s share-based compensation plans, including performance-based options:

The total intrinsic value of options exercised during the years ended December 31, 2020, 2019, and 2018 was approximately $3.5 million, approximately $5.1 million, and approximately $20.1 million, respectively. The intrinsic value was calculated as the difference between the fair value of the Company’s Class A Common Stock and the exercise price of the option issued.

The following table sets forth the Company's unrecognized share-based compensation expense, net of estimated forfeitures, as of December 31, 2020, by type of award and the weighted-average period over which that expense is expected to be recognized:

(1)	The weighted-average remaining recognition period cannot be determined for performance-based or time-accelerated options due to the nature of such awards, as detailed above.

The total unrecognized share-based compensation cost will be adjusted for future changes in estimated forfeitures.