Here's a current one, but there are a great many more papers on the subject if you hit Google Scholar or suchlike: http://schizophreniabulletin.oxfordjournals.org/content/earl...

However, the specific condition I was thinking of is 'Olney's lesions' (overview: http://www.camtriplehelix.com/journal/issue/3/breathing-in-t...). It should be noted that some critical research has been withdrawn in this area, which I had missed, so that raises questions about the accuracy of my original remarks: http://www.erowid.org/chemicals/dxm/dxm_health1.shtml