Neuralink, Elon Musk’s brain-chip company, aims to enroll three patients to evaluate its device in a study expected to take several years to complete, according to details on the U.S. government’s clinical trials database.

The company had sought to enroll 10 patients when it applied to U.S. regulators to begin clinical trials, Reuters reported last year. Neuralink is testing its implant designed to give paralyzed patients the ability to use digital devices by thinking alone, a prospect that could help people with spinal cord injuries.

Before Neuralink posted details of its trial this week, the company faced criticism from brain implant researchers and former regulatory officials for not sharing information about the study, as is common in the industry.

The U.S. Food and Drug Administration, which approved the clinical trial, said it generally likes companies to publish information about their studies to enhance public trust and honor patients who participate.

The FDA declined to comment on Neuralink, and company executives did not respond to a request for comment.

Neuralink’s study is estimated to have a primary completion date of 2026, with the full study expected to be complete in 2031. The study will enroll patients between the ages of 22 and 75 years with conditions such as quadriplegia.

According to eligibility criteria posted on the database, patients must have limited mobility without improvement for at least one year, with a life expectancy greater than or equal to 12 months.

Eligible patients must have very limited or no hand, wrist, and arm movement due to spinal cord injury or a neurological disorder called amyotrophic lateral sclerosis (ALS).

The “first-in-human early feasibility study” began in January, according to the registry details posted on Monday.

Early feasibility studies are exempt from a requirement to post trial details on the U.S. National Institutes of Health’s ClinicalTrials.gov website, but major medical journals often require trials to be registered on the database.

Neuralink has for years fielded calls from interested patients, well before the company received approval last year to begin conducting trials in people, Neuralink sources said.

The study uses a robot to surgically place a brain-computer interface (BCI) implant in a region of the brain that controls the intention to move, Neuralink had said.

In January, Neuralink implanted the device in the brain of its first patient, Noland Arbaugh, who is paralyzed from the shoulders down due to a 2016 diving accident.

The device has allowed Arbaugh to play video games, browse the internet and move a computer cursor on his laptop by thinking alone, according to company blog posts and videos.