Matthew Perry - Hair Transplant?

I've read around online, and some sources say that Matthew Perry had a hair transplant whilst he was still in Friends?

Is this true? I've been watching Friends a lot recently - it's repeated everyday on Comedy Central, and I only watch Comedy Central - and his hair always appears to be the same to me, a 'V' shaped hairline, even when the series started. If you look at pics of his hairline now, though, the widow's peak he had isn't really there, and his hairlines is now more straight.

So what's the deal?