Molecular imaging studies measuring CHRMs in people with schizophrenia have been possible using two non-selective single photon emission compute tomography (SPECT) tracers 3-quinuclidinyl-4-[123I] iodobenzilate (123I-QNB) and N-methyl-4-[123I] iododexetimide (123I-IDEX) that have high affinities for both the CHRM1 and CHRM4 (Muller-Gartner et al., 1992; Boundy et al., 1995; Piggott et al., 2002). Here, CHRM4 is linked to schizophrenia.