Comment on "Modafinil shifts human locus coeruleus to low-tonic, high-phasic activity during functional MRI" and "Homeostatic sleep pressure and responses to sustained attention in the suprachiasmatic area".

Minzenberg et al. (Reports, 12 December 2008, p. 1700) and Schmidt et al. (Reports, 24 April 2009, p. 516) reported blood oxygen level-dependent (BOLD) responses in the human locus coeruleus (LC). Here, we show that these LC responses do not correspond to the anatomical location of the LC and present cautionary data concerning the quality of BOLD signals measured from the LC using standard functional magnetic resonance imaging acquisition parameters.