Summary The discovery of the default mode network (DMN), a large-scale brain network that is suppressed during attention-demanding tasks, had major impact in neuroscience. This network exhibits an antagonistic relationship with attention-related networks. A better understanding of the processes underlying modulation of DMN is imperative, as this network is compromised in several neurological diseases. Cholinergic neuromodulation is one of the major regulatory networks for attention, and studies suggest a role in regulation of the DMN. In this study, we unilaterally activated the right basal forebrain cholinergic neurons and observed decreased right intra-hemispheric and interhemispheric FC in the default mode like network (DMLN). Our findings provide critical insights into the interplay between cholinergic neuromodulation and DMLN, demonstrate that differential effects can be exerted between the two hemispheres by unilateral stimulation, and open windows for further studies involving directed modulations of DMN in treatments for diseases demonstrating compromised DMN activity.

How do intrinsic brain dynamics interact with processing of external sensory stimuli? We sought new insights using functional magnetic resonance imaging to track spatiotemporal activity patterns at the whole brain level in lightly anesthetized mice, during both resting conditions and visual stimulation trials. Our results provide evidence that quasiperiodic patterns (QPPs) are the most prominent component of mouse resting brain dynamics. These QPPs captured the temporal alignment of anticorrelation between the default mode (DMN)- and task-positive (TPN)-like networks, with global brain fluctuations, and activity in neuromodulatory nuclei of the reticular formation. Specifically, the phase of QPPs prior to stimulation could significantly stratify subsequent visual response magnitude, suggesting QPPs relate to brain state fluctuations. This is the first observation in mice that dynamics of the DMN- and TPN-like networks, and particularly their anticorrelation, capture a brain state dynamic that affects sensory processing. Interestingly, QPPs also displayed transient onset response properties during visual stimulation, which covaried with deactivations in the reticular formation. We conclude that QPPs appear to capture a brain state fluctuation that may be orchestrated through neuromodulation. Our findings provide new frontiers to understand the neural processes that shape functional brain states and modulate sensory input processing.

Brain atlases play a key role in modern neuroimaging analysis of brain structure and function. We review available atlas databases for humans and animals and illustrate common state-of-the-art workflows in neuroimaging research based on image registration. Advances in noninvasive imaging methods, 3D ex vivo microscopy, and image processing are summarized which will eventually close the current resolution gap between brain atlases based on conventional 2D histology and those based on 3D in vivo imaging.

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29The anterior cingulate area (ACA) is an integral part of the prefrontal cortex in mice and has been 30 implicated in several cognitive functions. Previous anatomical and functional imaging studies 31 demonstrated that the ACA is highly interconnected with numerous brain regions acting as a hub region 32 in functional networks. However, the importance of the ACA in regulating functional network activity and 33 connectivity remains to be elucidated. Recently developed neuromodulatory techniques, such as Designer 34Receptors Exclusively Activated by Designer Drugs (DREADDs) allow for precise control of neuronal 35 activity. In this study, we used an inhibitory kappa-opioid receptor DREADDs (KORD) to temporally inhibit 36 neuronal firing in the right ACA of mice and assessed functional network activity and connectivity using 37 non-invasive functional MRI. We demonstrated that KORD-induced inhibition of the right ACA induced 38 blood oxygenation-level dependent (BOLD) signal decreases and increases in connected brain regions 39 throughout of hemispheres. Furthermore, these modulations in neuronal activity were associated with 40 decreased intra-and interhemispheric functional connectivity. These results demonstrate that the 41 combination of the DREADD technology and non-invasive functional imaging methods is a valuable tool 42 for unraveling the underlying mechanisms of network function and dysfunction. 43 44 45 Receptors Exclusively Activated by Designer Drugs (DREADDs), which are engineered receptors for 63 targeted enhancement or silencing of neurons upon binding of an otherwise inert ligand. The combination 64 of chemogenetics and non-invasive neuroimaging methods, such as functional magnetic resonance 65 imaging (fMRI), allows direct evaluation of DREADD-induced changes in neuronal firing on large-scale 66 neuronal activity and FC. As such, Giorgi et al. were able to causally link the chemogenetic activation of 67serotonergic neurons with neuronal activity increases in cortical and subcortical brain areas, measured by 68 relative cerebral blood volume increases [23]. Furthermore, other studies also used blood-oxygenation-69