Grant: Operating Grant

Visual, auditory, and other sensory stimuli presented to human subjects evoke increases in brain activity. Modern Magnetic Resonance Imaging scanners are capable of detecting such increases in neuronal activity in an indirect manner: they detect increased blood flow triggered locally by the increased neuronal activity. This method is termed 'functional Magnetic Resonance Imaging' (fMRI). Recent fMRI studies have demonstrated changes in brain activity not only when stimuli are presented to subjects, but also at rest. Importantly, these spontaneous (i.e. with no external stimuli) fluctuations in fMRI signals demonstrate 'functional connectivity': they increase or decrease in a synchronous manner over large parts of the human brain. It has been suggested that spontaneous brain activity is an important principle of brain function. This proposal is aimed at investigating the neuronal electrical activity that is represented by spontaneous changes in fMRI signals. We will pursue experiments that will determine the extent to which spontaneous fluctuations in fMRI signals reflect similar fluctuations in the underlying local neuronal activity. Furthermore, we will test whether the synchronization in spontaneous fMRI signals observed over remote regions of the brain (i.e., the functional connectivity) reflect synchronization in the overall level of neuronal activity measured within these areas. Last, we will pursue experiments towards understanding the mechanisms employed by neurons to mediate functional connectivity. To this end, optical imaging of blood oxygenation signals will be combined with neurophysiological recordings. The results may validate fMRI as a method for investigating spontaneous activity and functional connectivity in the resting state in healthy human subjects. Moreover, they may validate resting-state fMRI for diagnostic measurements in neurological and psychiatric diseases, based on changes in functional connectivity observed in these diseases.