Brains never rest

Whilst part of what we perceive comes through our senses from the object before us, another part (and it may be the larger part) always comes out of our own head.

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When William James, the preeminent psychologist and philosopher, wrote this he was largely referring to the notion that much of how we interpret the world depends on our prior knowledge and experiences. This suggests that we don’t perceive the world as it actually is, but rather as a dynamic sketch, approximating reality, which relies heavily on our conscious and/or unconscious personal histories.

When Marcus Raichle, neurologist and neuroscientist at Washington University, quoted James’ phrase in a recent article, he did so to draw a line from the psychological to the neuroscientific. It turns out that some of that stuff ‘coming out of our own head’ and impacting our perceptions might be related to intrinsic brain activity commonly referred to as the resting state. Of course all brain activity can be thought of as ‘intrinsic’ in its basic sense, but the notion behind intrinsic resting state activity is that there are areas of the brain that are most active when we’re not doing anything at all. In fact, although the brain is only 2% of your body weight, it uses around 20% of the energy you consume and most of that goes to resting state activity, like when you’re daydreaming or lying down – as opposed to stimulus-related activity.

What’s more, this resting state activity isn’t dispersed evenly throughout the brain, according mostly to brain imaging studies, but appears to show distinct patterns of activation. For instance, if you subtract the functional brain images taken of someone while they were performing a task from images of them taken when they’re asked to stare blankly ahead or when they close their eyes, you end up with a distinct pattern of activations (predominantly cortical and subcortical midline brain areas) known as the default-mode network.

If you take this same approach in some people with psychiatric disorders (like schizophrenia or major depression), you find that the resting state activity across the default-mode network is substantially altered. For instance, people with depression show higher resting state activity in many of these midline brain regions (e.g. perigenual anterior cingulate cortex, dorsomedial thalamus); the activity in the anterior cingulate, especially, may be related to the high degree of negative self-ruminations that many of these people experience. These same areas show increased activity in animal models as well, allowing for a more detailed understanding of the underlying neurobiology – although this line of research is just beginning (as, for instance, my colleagues and I discussed in a recent paper).

While understanding resting state activity has amazing potential implications for how we think about brain function and human behaviour, it’s far from clear what this all means. For example: Can we change our resting state activity, for example, through meditation? What would that mean at the psychological level in our everyday lives? Another issue is that although it may be important to further investigate resting state activity, the concept of a true resting state (i.e. the absence of any sensory information) seems to be methodologically impossible to achieve (e.g. it’s hard to get a sensory deprivation chamber into the MRI). Nonetheless, using multiple approaches to approximate the true resting state conditions, such as using imaging during eyes closed vs. eyes open while in a relaxed state etc., will allow neuroscientists to better understand its role – and could lead to many new insights into brain function.


References

Alcaro A, Panksepp J, Witczak J, Hayes DJ, Northoff G. 2010. Is subcortical-cortical midline activity in depression mediated by glutamate and GABA? A cross-species translational approach. Neuroscience and Biobehavioral Reviews 34:592-605.

Grimm S, Ernst J, Boesiger P, Schuepbach D, Hell D, Boeker H, Northoff G. 2009. Increased self-focus in major depressive disorder is related to neural abnormalities in subcortical-cortical midline structures. Human Brain Mapping 30:2617-27.

Northoff G, Duncan NW, & Hayes DJ (2010). The brain and its resting state activity–experimental and methodological implications. Progress in neurobiology, 92 (4), 593-600 PMID: 20888388

Raichle ME. 2010. Two views of brain function. Trends in Cognitive Science. 14:180-90.

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About davejhayes

neuroscientist.ca
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