Rat brains also have a default mode network

Abstract

The default mode network (DMN) in humans has been suggested to support a variety of cognitive functions and has been implicated in an array of neuropsychological disorders. However, its function(s) remains poorly understood. We show that rats possess a DMN that is broadly similar to the DMNs of nonhuman primates and humans. Our data suggest that, despite the distinct evolutionary paths between rodent and primate brain, a well-organized, intrinsically coherent DMN appears to be a fundamental feature in the mammalian brain whose primary functions might be to integrate multimodal sensory and affective information to guide behavior in anticipation of changing environmental contingencies.

Fig. 1.

Comparison of the DMN in rat, monkey, and human. For rat DMN (Left), significant clusters include: 1, orbital cortex; 2, prelimbic cortex (PrL); 3, cingulate cortex (CG1, CG2); 4, auditory/temporal association cortex (Au1, AuD, AuV, TeA); 5, posterior parietal cortex; 6, retrosplenial cortex, which corresponds to posterior cingulate cortex in humans; 7, hippocampus (CA1). (Center) Connectivity maps in the axial plane. Note the strong connectivity between prefrontal and posterior cingulate cortices, which can best be visualized in the sagittal plane (Bottom, medial-lateral: +0.4 mm). FrA, frontal association cortex; MO, medial orbital cortex; R, right; RSG/RSD, granular/dysgranular retrosplenial cortex. Color bar indicates t scores (n = 16, thresholded at t > 5.6, corrected P < 0.05). Numbers below images are approximate coordinates relative to bregma. For human DMN (Right), significant clusters include: 1, orbital frontal cortex; 2/3, medial prefrontal cortex/anterior cingulate cortex; 4, lateral temporal cortex; 5, inferior parietal lobe; 6, posterior cingulate/retrosplenial cortex; 7, hippocampus/parahippocampal cortex (n = 39, thresholded at z > 2.1, corrected P < 0.05). For monkey DMN (Center): 2/3, dorsal medial prefrontal cortex; 4/5, lateral temporoparietal cortex (including area 7a and superior temporal gyrus); 6, posterior cingulate/precuneus cortex; 7, posterior parahippocampal cortex. The monkey DMN map was derived using the cross-correlation method with the seed region shown (Bottom) [adapted from Vincent et al. (5)].

Fig. 2.

Functional correlation strengths between 13 brain regions within the DMN show the network separated into two modules: One is a parietal subsystem clustered at RSC, and the other is a temporal-prefrontal subsystem. Lines of different colors and widths represent correlation strength. The thickness of the lines reflects the strength of the correlation between regions. Cing, cingulate cortex (CG1 and CG2); PrL, prelimbic cortex; rAu/TeA and lAu/TeA, right and left auditory/temporal association cortex; rHip and lHip, right and left hippocampus; rOFC and lOFC, right and left orbital frontal cortex; rPPC and lPPC, right and left posterior parietal cortex; RSC, retrosplenial cortex (granular and dysgranular); rV2 and lV2, right and left secondary visual cortex.