Resting state functional coupling between the ascending synchronising system, limbic system and the default mode network via theta oscillations

In order to better understand dysfunction in dementia and psychiatric illnesses, the underlying neuronal systems that give rise to normal memory and cognitive processes need to be better understood. Based on electrophysiological recordings in animals, theta oscillations have been proposed as an intrinsic mechanism for the orchestration of memory functions, especially episodic and autobiographical memory. Theta oscillations are controlled by the ascending synchronising system, a set of nucleui in the pontine tegmentum and basal forebrain. At a network level, the default mode network has been shown to be responsible for episodic and autobiographical. Using resting state fMRI data, we show using an ICA approach, seed based connectivity and dynamic causal modelling that the ascending synchronising system is coupled to the medial temporal lobe nodes including the hippocampus and parahippocampal gyrus and with the default mode network. Our results provide thus support the role of theta oscillations in memory function and coordination at a network level. Highlights Resting state functional coupling between the DMN, MTL and ascending synchronising system. Theta oscillations may be the basis of this coupling given the role of these structures in control of theta. Theta oscillations have been implicated in memory, cognition and predictive coding. DMN, MTL and ASS are implicated in Alzheimer’s disease. Abbreviations MRI Magnetic resonance imaging fMRI functional magnetic resonance imaging rs-fmri resting state functional magnetic resonance imaging PnO Pontine nucleus oralis SuM Supra-mamillary nucleus. MS Medial septum DB Diagonal band of Broca. VTA ventral tegmental area PCC Posterior cingulate cortex HC Hippocampus ARAS Ascending reticular activating system ASS Ascending synchronising system DMN Default Mode Network aMPFC Anterior Medial Prefrontal Cortex pIPL Posterior inferior parietal lobule NBM Nucleus Basalis Mynert DCM Dynamic causal modelling PHG Parahippocampal Gyrus