It's ongoing - out of curiosity, I started going through some search results, surprising number on pubmed, and fun stuff on google.
Here's someone at IU who seems to be into it.
Here's a fun one indicating that cultural pressure back to the medieval time hasn't affected the distribution.
The left side speech and right handedness has been postulated but I don't think it has much to support it. It's one of those fun conundrums.