Musk's neurotechnology company in January installed a brain implant in Noland Arbaugh, the company's first human test subject, which the billionaire head of Tesla and X touted as a success.

Arbaugh was left paralyzed from the shoulders down by a diving accident eight years ago.

Shortly after the implant operation, he told of playing chess and the videogame "Civilization," as well as taking Japanese and French lessons by controlling a computer screen cursor with his brain.

Neuralink's technology works through a device about the size of five stacked coins that is placed inside the human brain through invasive surgery, of which the threads are a key signal collecting component.

A company blog post on Wednesday said threads connecting the implant to Arbaugh's brain recently "retracted... resulting in a net decrease in the number of effective electrodes" and the patient's ability to operate the cursor.

While offering no explanation for the receding threads, the company said it made modifications to make the implant more sensitive to neural signals.

This, with other improvements, "produced a rapid and sustained improvement in bits-per-second, that has now superseded Noland's initial performance."

The drop in the implant's efficiency was first reported by the Wall Street Journal.

The startup, cofounded by Musk in 2016, aims to build direct communication channels between the brain and computers.

The ambition is to supercharge human capabilities, treat neurological disorders like ALS or Parkinson's, and maybe one day achieve a symbiotic relationship between humans and artificial intelligence.

Musk is not alone in trying to make advances in the field, which is officially known as brain-machine or brain-computer interface research.