and any resulting gain or loss is included in the results of operations. Advances paid towards the acquisition of property and equipment, and the cost of property and equipment not ready for use before the end of the period, are both classified as construction in progress.
Impairment of Long-Lived Assets
Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment charges during any of the periods presented.
The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing and commercializing gene therapy treatments for patients suffering from rare and life-threatening neurological genetic diseases. All of the Company’s tangible assets are held in the United States.
Research and Development Costs
Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, third party license fees, and external costs of outside vendors engaged to conduct manufacturing and preclinical development activities and clinical trials.
Upfront and milestone payments made to third parties who perform research and development services on the Company’s behalf are expensed as services are rendered or when they no longer have alternative future use. Costs incurred in obtaining technology licenses through asset acquisitions are charged to research and development expense if the licensed technology has not reached technological feasibility and has no alternative future use.
All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.
The Company accounts for its stock-based compensation awards in accordance with FASB ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock units, to be recognized in the consolidated statements of operations based on their fair values.
The Company’s stock-based awards are subject to service and performance-based vesting conditions. Compensation expense related to awards to employees with only service-based vesting conditions is recognized on a straight-line basis over the requisite service period for each separately vesting portion of the award as if the award was, in substance, multiple awards (the “Graded Vesting Attribution Method”), based on the estimated grant date fair value