The brain is never at rest. Whether performing a task or mind wandering, the human brain exhibits a rich mixture of transient, evoked activity and ongoing spontaneous fluctuations, reflecting the non-stationary and dynamic nature of neuronal activity. This activity connects functionally specialized but widely distributed cortical regions in order to support complex cognitive functions. The non-stationary nature of neuronal communication across functional networks has been traditionally imaged in a non-invasive manner with EEG and MEG. There are some functional MRI studies of functional brain connectivity, mostly performed with resting state data and assuming stationarity in the BOLD dynamics. Complex cognitive abilities are likely to impact the way functional brain networks interact. Bilingualism seems to have this effect, as bilinguals perform differently than monolinguals in multiple behavioural and cognitive domains that require interaction between functional networks. This project will clarify the non-stationary dynamics of spontaneous brain activity and large-scale functional networks, and their relation with behaviour and cognition in bilingual and monolingual individuals. By deploying a multidisciplinary approach and using behavioural and neuroimaging data, this project will identify the electrophysiological correlates of transient BOLD activity in the resting state. We will assess their relation to low frequency, spontaneous haemodynamic fluctuations and ongoing oscillatory electrical activity across large-scale functional networks, and also investigate the physiological substrate of the “bilingual advantage” in tasks involving executive control and the “bilingual disadvantage” in lexical access tasks. High-proficiency Basque-Spanish bilinguals, who manage two languages with no common linguistic rules in one brain, are perfectly suited to investigate these questions.