fid = '2012_03_05_Lollipop-10803_Long-Term-optoBB_CNQX_00_pre-drug';
t_end = loadspk([fid '.spk'],'last');
spk = loadspk([fid '.spk'],[0 t_end],0);
ss = SqueakySpk(fid,spk.meta.fs_Hz,1,spk);

length(ss.time(ss.unit>0))/max(ss.time)/max(ss.unit)