The Company recognized total stock-based compensation expense during the three months ended March 31, 2023 and 2022 as follows (table in thousands):


	Three Months Ended March 31,
	2023		2022
Service-based awards:

Restricted stock units	$	45	$	12
Stock option awards	148		200
Total Service Based Awards	193		212
Performance-based awards:
Restricted stock awards	—		(391)


Total Performance Based Awards	—		(391)
Total	$	193	$	(179)

A summary of the Company’s restricted stock awards during the three months ended March 31, 2023 is as follows:


	Number of Shares	Weighted Average Grant-Date Fair Value
Unvested at January 1, 2023	891	$	62.70

Unvested at March 31, 2023	891	$	62.70

A summary of the Company’s restricted stock awards during the three months ended March 31, 2022 is as follows:


	Number of Shares	Weighted Average Grant-Date Fair Value
Unvested at January 1, 2022	7,118	$	62.70
Forfeited	(6,227)	$	62.70
Unvested at March 31, 2022	891	$	62.70

The fair value of restricted stock awards are measured based on their fair value on the date of grant and amortized over the vesting period of 20 months. As of both March 31, 2023 and 2022, unvested restricted stock awards of 891 were related to performance-based awards. The forfeited performance-based restricted stock awards of 6,227 was due to the resignation of the Company's Chief Development Officer on March 25, 2022. These forfeited awards reduced stock-based compensation expense by $0.4 million in 2022.

A summary of the Company’s service-based restricted stock units during the three months ended March 31, 2023 is as follows:


	Number of Shares	Weighted Average Grant-Date Fair Value
Unvested at January 1, 2023	125,000	$	1.47



Unvested at March 31, 2023	125,000	$	1.47

A summary of the Company’s service-based restricted stock units during the three months ended March 31, 2022 is as follows:


	Number of Shares	Weighted Average Grant-Date Fair Value
Unvested at January 1, 2022	29,289	$	12.87


Forfeited	(1,223)	52.91

Unvested at March 31, 2022	28,066	$	11.11

The fair value of service based restricted stock units are measured based on their fair value on the date of grant and amortized over the vesting period. The vesting periods range from 1 to 3 years. Stock-based compensation expense of $45,184 and $12,000 was recognized for the three months ended March 31, 2023 and 2022, respectively. As of March 31, 2023, the unrecognized stock-based compensation expense was $34,139, which is expected to be recognized over an estimated weighted average remaining term of less than 1 year.

A summary of the Company’s service-based stock option activity for the three months ended March 31, 2023 is as follows:


	Shares Underlying Options	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding at January 1, 2023	1,206,905	$	8.32	8.9


Forfeited	(8,083)	3.54		—
Expired	(4,620)	18.44		—
Outstanding at March 31, 2023	1,194,202	$	8.32	8.6

Exercisable at March 31, 2023	239,075	$	28.45	6.7

A summary of the Company’s service-based stock option activity for the three months ended March 31, 2022 is as follows:


	Shares Underlying Options	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding at January 1, 2022	528,591	$	32.01	7.5
Granted	909	4.07		9.9
Forfeited	(14,839)	17.49		—
Expired	(3,545)	85.36		—
Outstanding at March 31, 2022	511,116	$	32.01	7.0

Exercisable at March 31, 2022	230,858	$	54.56	5.0

The aggregate intrinsic value is calculated as the difference between the closing price of the Company's common stock and the exercise price of the stock options that had strike prices below the closing price. The intrinsic value of the outstanding options were not significant for all periods presented.

During the three months ended March 31, 2023, the Company granted no stock options to purchase shares of common stock. During the three months ended March 31, 2023, 8,083 shares were forfeited and 4,620 shares expired. Forfeitures are recorded in the period of occurrence and compensation expense is adjusted accordingly.

Stock-based compensation expense recognized for service-based stock options was $0.1 million and $0.2 million for the three months ended March 31, 2023, and 2022 respectively. As of March 31, 2023, total stock-based compensation expense related to unvested options not yet recognized totaled approximately $0.7 million, which is expected to be recognized over an estimated weighted average remaining term of 8.64 years.