NOTE 11 — STOCK-BASED COMPENSATION

Stock-based compensation expense, which consists of the compensation cost for employee stock options and the value of options issued to non-employees for services rendered, was allocated to research and development and general and administrative in the consolidated statements of operations as follows (in thousands):

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As of June 30, 2023, the total unrecognized compensation cost related to unvested stock-based awards granted to employees under the Company’s equity incentive plans was approximately $8.6 million. This cost will be recorded as compensation expense on a ratable basis over the remaining weighted average requisite service period of approximately 2.4 years.

Valuation Assumptions

The Company estimated the fair value of stock options granted using the Black-Scholes option-pricing formula and a single option award approach. This fair value is being amortized ratably over the requisite service periods of the awards, which is generally the vesting period.

The fair value of employee stock options was estimated using the following weighted-average assumptions:

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Equity Incentive Plans

These plans consist of the 2018 Equity Incentive Plan, the 2014 Equity Incentive Plan, as amended; the 2004 Amended and Restated Equity Incentive Plan; and the Amended and Restated 2004 Employee Stock Purchase Plan. As of May 31, 2018, the 2014 Equity Incentive Plan; and the 2004 Amended and Restated Equity Incentive Plan were terminated, and no further shares will be granted from those plans.

The following table summarizes stock option activity under the Company’s equity incentive plans:

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The total intrinsic value of stock options exercised during the six months ended both June 30, 2023 and 2022, was zero, as determined at the date of the option exercise.

Cash received from stock option exercises was zero, for the six months ended both June 30, 2023 and 2022. The Company issues new shares of common stock upon exercise of options.