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.functional MRI | resting state | intrinsic activity | connectivity | spontaneous fluctuation I n the absence of an immediate need for goal-directed attention to the surrounding environment, our minds wander from recollection of past happenings to imagination of future events. Neuroimaging studies have consistently identified a set of interconnected brain areas that becomes less active during attentiondemanding cognitive tasks (1). This so-called default mode network (DMN) is posited to play a fundamental role in brain organization and supports a variety of self-referential functions such as understanding others' mental state, recollection and imagination (2), conceptual processing (3), and even in the sustenance of conscious awareness (4). Many of these functions have been considered to be unique to humans. Intriguingly, similar coherent structures have been shown to exist in anesthetized macaque monkeys and chimpanzees (5, 6). Furthermore, the functions of the default network are disrupted in such neuropsychological disorders as schizophrenia, Alzheimer's disease, and autism (7-9), underscoring the clear and critical need for further investigating the neurobiological basis of DMN using animal models.The evolutionary clade of rodents is about 35 million years earlier than that of old world monkeys and about 60 million years earlier than humans (10). Although many of the structures and functions of subcortical nuclei are conserved across these three species, the neocortex, in particular the "association" cortex, has extensively expanded in the primate as a result of evolutionary pressure, which is considered to be crucial in the development of higher cognitive and behavioral functions (10, 11). On the other hand, such structures as cingulate cortex, prefrontal cortex, and hippocampal formation, all of which are critical elements of the DMN, are also present in rodents (11). Given the distant evolutionary paths between rodent and primate brain, an intriguing question arises: Does the rat possess a similar DMN? Such a network, once demonstrated, would not only suggest that an operational DMN is a common feature in the mammalian brain, perhaps induced via parallel evolution as a result of natural selection, it would also offer a novel platform to explore the physiological basis and behavioral significance of the DMN. Such a demonstratio...

Mesoscale infraslow spontaneous membrane potential fluctuations recapitulate high-frequency activity cortical motifs

“…We demonstrated that infraslow spontaneous cortical activity exhibits an intrahemispheric activity structure that is strikingly similar to that of cortical motifs, characteristic patterned activity whose occurrence reverberates within slow spontaneous activity. Functional connectivity emanating from rodent retrosplenial cortex has features thought to be consistent with analogous connectivity from human DMN 6 . Interestingly, correlation maps generated from infraslow VSD activity recapitulated features of the rat DMN identified by fc-fMRI 6 .…”

“…Functional connectivity emanating from rodent retrosplenial cortex has features thought to be consistent with analogous connectivity from human DMN 6 . Interestingly, correlation maps generated from infraslow VSD activity recapitulated features of the rat DMN identified by fc-fMRI 6 . Noteworthy is the recruitment of medial cortices extending anteriorly toward, and encompassing aM2/CG.…”

“…To assess the spatiotemporal structure of specifically infraslow spontaneous activity, we down-sampled our acquired imaging data by integrating video frames to a sampling rate of 1 Hz and then applied a zero-phase lag Chebyshev bandpass (0.02-0.08 Hz) filter. This frequency band was selected on the basis of previous reports of infraslow activity in rodents and our own measurements of VSD signal power and functional structure 6,7,38,39 . We observed fluctuations in the resultant VSD signal ( Supplementary Fig.…”

“…Intriguingly, these structures are also consistent with cortical features recently described as components of the rat analogue of the DMN identified from fc-fMRI. In particular, prefrontal cortex and retrosplenial cortex were identified as hubs, comprising two distinct modules of the rat default network 6 . These results are also broadly similar to functional resting-state connectivity exhibited using intrinsic signal optical imaging, which reflects inherently infraslow processes in mice 7 and suggests common consistent features of infraslow, resting-state, bilateral connectivity across imaging modalities.…”

“…From its early description as 'infraslow' 4 , spontaneous or resting-state activity at this very low-frequency domain (o0.1 Hz) has been observed as a consistent feature of ongoing brain activity across different species [4][5][6][7] and across different brain states 5,[8][9][10] , though its precise function and mechanistic underpinnings remain unclear. In the developing brain, electrophysiological infraslow activity in the form of neuronal activity transients or bursting activity has been linked with the development of neuronal networks 11,12 , whereas in the adult brain, infraslow activity has been demonstrated to synchronize with higher-frequency brain activity 13,14 and to correlate to variability in behavioural performance 15,16 .…”