Doggie Daydreams – The Default Mode Network

“What do tigers dream of when they take their little tiger snooze?
Do they dream of mauling zebras, or Halle Berry in her Catwoman suit?”
– Stu’s Song, The Hangover.

You sit down, relax…thinking of nothing. It would be reasonable to assume that in this resting state your brain is also taking a break. That’s not entirely true. Some areas of your brain increase their activity, not only that but they are communicating with each other. Together they make up the Default Mode Network (DMN).

A little over a decade ago neuroscientists thought that when a person was doing nothing the brain followed suit. That is the brain circuits were also resting whenever a person was at rest. Brain activity while at rest was seen as white noise, random firings with no specific purpose.

In 2001 Raichle used PET imaging to forever change this view of the brain. Raichle identified specific areas of brain circuitry that show elevated blood flow – indicating greater metabolic activity – during rest than while engaged in cognitive tasks.

It was later shown these regions showed functional interconnectivity during resting states – a network. Several years later a comparable network was found in non-human primates, specifically macaques and chimpanzees.

“Rat brains also have a default mode network.”; a remarkable title given that until 11 years ago this phenomenon was unknown and until 5 years ago it was thought to be a uniquely human trait. Like so many other ‘uniquely’ human traits – tool use, altruism, culture, empathy – it turns out we are not all that unique.

“[In humans the] default mode network (DMN) is posited to play a fundamental role in brain organization and supports a variety of self-referential functions [my emphasis] such as understanding others’ mental state, recollection and imagination, conceptual processing, and even in the sustenance of conscious awareness.”

Not exactly the traits people think of when they consider animal mind. And of course, just because that’s the role they play in our brain organization doesn’t mean it’s the same for other animals. But it is also unlikely that it is fundamentally all that different.

“proposed rat DMN share two common features: (i) They receive high-order information from virtually all sensory modalities, and (ii) they have direct or indirect connections with such limbic structures as hippocampus and amygdala, suggesting the involvement of memory and emotional behavior.”1

“We propose that the primary function of the rat DMN might be to evaluate internal and external body states by assessing information from multiple sensory modalities and, by integrating with past experience, to anticipate changing environmental contingencies.”1

IOW, the animal is always on alert. And if you’ve ever seen a seemingly placid dog burst  into life, rush to a window to bark his head off; you know this is true.  And now you know how it happens.

So next time you look at your dog doing nothing, think again: his brain is hard a work.

REFERENCES

1. Hanbing Lu, Qihong Zou, Hong Gu, Marcus E. Raichle, Elliot A. Stein, and Yihong Yang. Rat brains also have a default mode network. PNAS 2012 109: 3979-3984 

2. Michael D. Greicius, Ben Krasnow, Allan L. Reiss and Vinod Menon.
   Functional Connectivity in the Resting Brain: A Network Analysis of the Default Mode Hypothesis. PNAS January 7, 2003 vol. 100 no. 1 253-258