We assume you are using the SPSS, Stata, or SPSS data package. To identify the columns see the accompanying code file. For example, if you are working with the SAS package see ADNIMERGE_SAS/code/clielg.sas, specifically the lines:

INFILE "../data/clirev.csv"
DSD
LRECL= 321 ;
INPUT
ORIGPROT
COLPROT
RID
SITEID
VISCODE
USERDATE
V1
CLIPASS
CLIDATE
CLICOMM
CLIPASSWD
;
LABEL ORIGPROT = "Protocol from which subject originated" ;
LABEL COLPROT = "Protocol under which data was collected" ;
LABEL RID = "" ;
LABEL SITEID = "" ;
LABEL VISCODE = "" ;
LABEL USERDATE = "" ;
LABEL V1 = "USERDATE2" ;
LABEL CLIPASS = "" ;
LABEL CLIDATE = "Approval Date" ;
LABEL CLICOMM = "Comments:" ;
LABEL CLIPASSWD = "I certify that I am using my own personal username and password and understand that by using my username and password, I am authorizing this electronic signature to be the legally binding equivalent of my handwritten signature executed on paper. Enter Your Password:" ;
FORMAT CLIPASS CLIPASS. ;
FORMAT USERDATE yymmdd10.;
FORMAT V1 yymmdd10.;
FORMAT CLIDATE yymmdd10.;
RUN;