How to See What you are Looking For in fMRI and PET – or the Crucial Baseline Condition

The conditions of eyes open or eyes closed in complete darkness have served as REST in human brain imaging studies. However, the mere transition from lid closed to lid open could theoretically cause non-trivial differential effects on brain activity without there being any change in external sensory stimulation or behavioral tasks. As a matter of fact, the lid drives the brain to regularly and repeatedly activate different cortical networks. The ocular-motor and attentional systems were activated when the eyes were open; in contrast, the visual, somatosensory, vestibular, and auditory systems were activated when the eyes were closed. These data suggest that there are two different states of mental activity: An „interoceptive“ state with the eyes closed which is characterized by imagination and multisensory activity, and an „exteroceptive“ state with the eyes open which is characterized by attention and ocular-motor activity [1]. In a subsequent study the impact of the chosen rest condition – eyes open or eyes closed in complete darkness – on the pattern of brain activations during visual stimulation was evaluated in healthy volunteers [2]. This showed that the choice of rest condition is critical for stimulus-induced brain activation pattern. Activity of the ocular-motor system as well as deactivation of sensory cortical areas may go undetected with eyes open as rest condition. References: [1] Marx E, Stephan T, Nolte A, Deutschländer A, Seelos KC, Dieterich M, Brandt Th. Eye closure in darkness animates sensory system. NeuroImage 2003; 19: 924–934. [2] Marx E, Deutschländer A, Stephan T, Dieterich M, Wiesmann M, Brandt Th. Eyes open and eyes closed as rest conditions: impact on brain activation patterns. NeuroImage 2004; 21: 1818–1824