Some purchases by bullish investors boosted the valuation in recent months, ahead of Neuralink's May 25 announcement that U.S. regulators had approved a human trial on its brain chip, the sources said.
The stock transactions at a valuation of around $5 billion have been carried out by shareholders such as employees and the company's early backers, rather than Neuralink selling new shares to investors. Such so-called secondary trades are an imperfect gauge of a company's value; their volume is thin and they lack the wider market consensus of a fundraising round or initial public offering .
Many of the recent stock sales have been to relatively small investors, who typically focus more on getting a slice of a company owned by Musk than scrutinizing its valuation. The maximum amount sought for the Neuralink shares marketed for sale at a $7 billion valuation was just $500,000, according to the email seen by Reuters.
"A study to assess safety and tolerability is in no shape or form valid to justify a $5 billion valuation," said Sridhar, who helped launch Galvani Bioelectronics, a developer of implants backed by GSK Plc and Alphabet Inc's Verily Life Sciences. Galvani is not a competitor of Neuralink because its implants under development will be installed in an artery to the spleen to help treat rheumatoid arthritis, rather than the brain.