Imagine a human brain sitting in a chair, laughing at our clumsy attempts to figure out how it works. It's an image that comes to neuroscientist Dr. Georg Northoff, as he writes books and plays about the brain, when he's not busy investigating its neural mysteries.

"I always imagine when I do these plays, there sits a brain beside us, and I'm sure the brain would smile and say 'they're so stupid,' " he said.

It's a pretty cheeky attitude for a mass of neural tissue Northoff describes as 'pulp.'

"You'll see in my play, I describe it as 'gruesome grey pulp.' If you consider the brain from the outside, if you just take it out of the skull, it's just grey, jelly matter," he said. "Inside the brain, it's a collection of neurons, a collection of molecules…I would argue it is some spatial, structural, temporal template which is continuously changing, like a grid. I hope that in 10 years, I can tell you more."

Northoff holds the Canada Research Chair in Neuropsychiatry at the University of Ottawa and he's also part of the Mind, Brain Imaging and Neuroethics Research Unit at the Royal Ottawa Mental Health Centre. As he studies the biochemical basis of mental illness, Northoff believes he's also on the trail of the elusive seat of consciousness, the part of the brain that creates our unique sense of self.

"You always feel like you are yourself. When you got up this morning and looked in the mirror, you weren't surprised by what you detected in the mirror. It was yourself. You immediately recognize yourself," Northoff said.

The brain's default mode network could be orchestrating all networks during cognition, says neuroscientist Dr. Ruth Lanius. (CBC)

That complex experience of being 'you' is a feeling that is unique to every individual, but that sense of being special is rooted in brain chemistry and neuronal wiring that neuroscientists are just beginning to understand.

Northoff explains it this way: If you see a picture of the town where you live, a particular area of the brain will become active, especially an area in the middle of the brain, the cortical midline structure. But if you see a picture of another town, with no special personal relevance, the cortical midline structure does not become active.

In other words, researchers believe they now know what the brain looks like when it recognizes 'home.'

It's part of an effort to understand a mysterious neural network only recently described, called the "default mode network," a stark name for what some believe could ultimately harbour the secrets of the soul.

Researchers find the brain at rest is still active

Researchers stumbled upon this network in the mid-1990's, during a series of experiments designed to investigate something else. In those days, researchers were focused on what happens in the brain when it is doing a specific task, such as recalling a memory or reading.

There was little interest in what the brain is doing when it was not engaged, until scientists noticed a curious change in the normal resting state of the brain and decided to take a closer look.

When they investigated what the brain is doing when it isn't busy thinking, they began to see a network of neural activity that seems to become most active when the brain is doing nothing at all. Scientists became further intrigued because, even though the brain appears to be idle, it is using a startling amount of energy.

"It consumes 20 per cent of your body's energy," Northoff said. "So why so much energy, for such a small organ? We don't know."

The default mode network uses much more energy than conscious thought. When the brain does do some heavy mental lifting, the activation of the resting state only decreases by about two per cent, a mere flutter, and it hums along, in the background, continuing to chew up a significant amount of energy for a neural function scientists don't really understand.

"It does a lot of important work that we don't know, in the dark. We have no idea at the moment why it exists, this resting state activity, and what it does, what the purpose of it is," Northoff said.

The dark side of the brain is always working

The default mode network is always on, and perhaps it's always on because our sense of 'self' is always on.

"Which makes sense," Northoff said, "because your intrinsic activity is always with you and your sense of self is always with you. But that is really subject to future research. Our working hypothesis is that the intrinsic activity is central for constituting your sense of self and ultimately also consciousness."

"It could be running the whole show," said Dr. Ruth Lanius, a neuroscientist at Western University in London, Ont. "It may even be orchestrating all the networks that are active when we engage in cognitive tasks. So this default mode network may serve like a conductor of the whole orchestra that really sets the brain in what it needs to engage in the future and what it needs to respond to."

Another curious question has emerged from Lanius' research. Why does the default mode network appear fractured in people who have experienced childhood trauma? Using brain imaging technology, she has shown that adults who experienced childhood abuse have a default mode network pattern that resembles the pattern of a seven-year-old child.

Neuroscientists hypothesize that some of the disruptions scientists see in the brain's default mode network in people with PTSD related to childhood trauma may be related to a damaged sense of self. (CBC)

"It may be related to the fact that stress hormones that are present as a result of childhood abuse may be hampering the development of the fibre tracts and myelination of the fibre tracts that needs to happen in order for this network to develop appropriately," she said.

So, if the default mode network truly is the seat of the 'self,' could a disruption in the network explain some of the suffering caused by post traumatic stress disorder (PSTD)?

"Yes," Lanius said. "We were hypothesizing that maybe some of the disruptions that we see in the default mode network of people with PTSD related to childhood trauma may be related to the often-damaged sense of self these people experience."

A clue to mental illness

Researchers also hypothesize that damage to the default mode network might explain other mental illnesses. Back in Ottawa, Georg Northoff is studying the default mode network in depressed patients.

With depression, "you're completely detached and disassociated from the environment," Northoff said. "Your focus is just on yourself and on your body and you feel pain and emotions, but you don't connect to the other person anymore. You feel disconnected."

It's as though depressed patients are somehow stuck in a state of inner reflection, unable to easily switch back to engagement with the outside world.

Dr. Georg Northoff is studying the brain's default mode network in people with depression. (CBC)

"We have findings, very solid findings, that in depression you have certain regions with abnormally high intrinsic activity, in other regions, it's abnormally low," Northoff said. "We assume, and there's pretty solid evidence, that that is related to abnormalities in the resting state. They're somehow trapped in their own self, and ultimately, trapped in their own resting state, and they cannot get out of that."

If researchers can understand the function of the default mode network, and the difficulties associated with disruptions, they hope it will lead to better diagnosis and treatment for mental illness, and perhaps one day doctors will be able to predict who is vulnerable.

"That's what we hope. That's exactly why we focus a lot of our investigation now on the intrinsic activity and also how that intrinsic activity relates to the environment and previous life history," Northoff said.

"I hope that in five or 10 years, we are there. At least, the work goes in this direction, but I think we need to understand much better how the brain really works. Philosophically, this is the old question for the mind-brain problem, how our mental state, like free will, consciousness, self, relate to the brain."

And this is when he senses that laughing brain, again, amused by scientific efforts to disentangle its various functions. Northoff says his imaginary brain is smiling and thinking, 'Intrinsic, extrinsic, for me I don't care.'

"I could vividly imagine the brain saying 'Come on, you're distinguishing between biological and social. I don't care, I'm both!' Outside, inside, for the brain, it doesn't matter."

This is part three of a four part series called Inside Your Brain on CBC's The National, World at Six and CBC.ca exploring how modern neuroscience is changing the way we think about the way we think. In part four Kelly Crowe explores the illusion of memory, why memories feel permanent but they are not.