The following table summarizes option activity:

On August 2, 2022, our Board of Directors, or Board, modified the outstanding options to purchase common stock under our 2015 Omnibus Equity Incentive Plan, or 2015 Plan, to allow for the acceleration of vesting of all unvested 2015 Plan options in the event of a change in control through the election of a majority of new members to our Board.

On August 15, 2022, the Special Meeting was held at the request of Activist, to increase the size of our Board from five members to eleven members and elect Activist’s slate of six nominees to serve as directors in addition to the existing five Board members. As a result of the change of control, all unvested options granted under the 2015 Plan prior to August 15, 2022, immediately became vested. We recognized approximately $0.5 million of stock-based compensation during the three months ended September 30, 2022.

During the three-month period ended September 30, 2022, our Board granted 125,000 options to purchase common stock at $1.52 per share and 900,000 options to purchase common stock at $1.31 per share which are subject to shareholder approval of an amendment to increase the number of shares reserved for issuance under our 2015 Plan. The options vest monthly over a 12-month period from the grant dates. As the shares underlying these options have not been approved by our stockholders, they have been excluded from the table above as of September 30, 2022.

The following table summarizes the stock-based compensation expense recorded for awards under our stock option plans (in thousands):

We use the Black-Scholes-Merton option-pricing model with the following assumptions to estimate the fair value of our stock options:

As of September 30, 2022, there was approximately $1.1 million of total unrecognized compensation expense related to non-vested stock options subject to shareholder approval. This expense is expected to be recognized over a weighted-average period of approximately 1.0 year.