Changes in arterial O
saturation and PO
and examples of whole pattern activation. (a) Changes in arterial O2 saturation and PO2 under different O2 gas concentrations during anaesthesia. These parameters can affect the BOLD response during MRI; therefore, it is important to monitor blood gas levels during such functional MRI studies . (b c) Example of whole pattern activation in a rat brain erratically induced by too deep isoflurane anaesthesia. Such a ‘bad’ activation pattern in the whole brain (c) would mask any specific activation due to a pharmacological and/or sensorial stimulus, and in this case, the time course shows (b) a general decline in signal, and no effect of the challenge is visible.