“…Some reports, mainly from studies performed at high magnetic fields, confirmed the initial dip (Ernst and Hennig, 1994;Menon et al, 1995;Logothetis et al, 1999;Yacoub and Hu, 1999;. Those confirmations, however, remained somewhat isolated because the initial dip, whose amplitude grows more rapidly with the field strength than the positive BOLD response (Yacoub and Hu, 1999), was missed in most of the low-field studies (Fransson et al, 1998;Mandeville et al, 1999a;Marota 1999, but see Yacoub and Hu, 1999) and even in some high-field experiments (Silva et al, 2000); in any case, when investigated with BOLD fMRI, the initial dip appeared to be somewhat elusive (Logothetis, 2000versus Kim, 2000. In addition, doubts were raised with respect to the accuracy of the [Hbr] and the oxyhaemoglobin concentration ͓͑HbO 2 ͔͒ time courses calculated by Malonek and Grinvald in their 1996 paper, since those had been obtained with a classical Beer-Lambert spectroscopic model, which approximates the optical path as constant rather than taking its wavelength dependency into account (Cope et al, 1991;Arridge et al, 1992).…”