Does Our Brain Have a Default Mode?
Think about it. When awake, we wander through the world taking in an enormous amount of information at all times. Our brain is always active, perceiving and interpreting all stimuli and responding to the environment as we go. However, is the external the only thing that stimulates and affects our brain? The only thing that guides its activity and determines its course? Or is there some kind of internal activity, some “default” processes that are always engaged, some kind of intrinsic activity of the brain?
Ever since we came upon the possibility of revealing our brain’s activity through neuroimaging techniques, neuroscience has been the prominent approach in the discovery and research of all kinds of psychological processes — perhaps more than you can imagine. Tactile discrimination, visual attention, imagination, speech, reading, human-face recognition… have all been put to test in order to see which brain regions and at which intensity they activate. Ideally, this explains something about all of these processes. In reality, and only if done correctly, we obtain a slight hint of where in the brain these processes might be occurring.
Something showed up consistently across many of these experiments, specifically in the ones using functional magnetic resonance imaging (fMRI). This technique allows one to see during the task you aim to unveil (e.g., visual attention) which brain areas are active. The issue is that this is usually calculated comparatively to a baseline. For registering active brain areas in visual attention, for example, we would compare the brain activity of some follow-the-dot task to an eyes-closed period, this is because with eyes closed we are sure no visual attention is occurring. A simple subtraction should tell us which are the specific areas involved in the process of visual attention. Problem solved.
But an unexpected discovery arouse from this technique: even during eyes-closed (“baseline” or “resting state”) some regions were active, they were found to deactivate when engaging in the task and to reactivate when the task was over. In other words, there was some brain activity that, no matter the task, arouse when entering a resting state after the trial. Some kind of consistent brain activation was found that anti-correlated with paying attention to external stimuli (this was captured by the experimental task, e.g., a dot you were instructed to follow, a sound you were told to discriminate, etc.). The problem was to figure out what this activity was. What was the brain doing when resting?
There were roughly speaking two ways of looking at it. Either this activity “served” external tasks, so it was merely a “resting” or “disconnected” state which ceased whenever you attended the exterior world again, or it was a state of its own, with proper functions, not merely defined by the absence of outside perturbations, but by the processes that our brain intrinsically and continuously brings about. But then the following question was raised: Why not both? Something that ceases whenever we attend to an outside stimulus and that our brain engages in by default. This is the direction many of the experiments took. And for this reason, this patterned brain activation was named “Default Network” or “Default Mode Network”. We only had to find out what it did.
Just to clarify, there are obviously many “default” functions that our brains need to perform; we need to be open to our environments and ready to respond to potential threats so some internal mechanisms need to be always running (ensuring our body posture (sitting, standing…), hormonal and other homeostatic mechanisms, etc.). However, what we are looking for is a cognitive function. Not what makes us a functional organism that continues living, but something that plausibly supports and constitutes the continuity of our cognitive activity.
Imagine yourself reading a book. It is one you are not fully engaged on anymore, it’s been 30 minutes and your attention starts to fade. You realize you’ve finished the page but you don’t have any clue about what you just read. Sounds familiar? Well, this is exactly where the Default Mode Network (DMN) comes in. Your mind goes “somewhere”, but this “where” is not really controlled by you. It is actually your mind “doing its thing” whenever it has the chance. It makes sense that the best time to do that is when no external attention is needed. And that if you force yourself to keep reading, the mind-wandering ceases and the DMN stops being active.
But then, what exactly goes on when we mind-wander? Mind-wandering and distraction were in fact the first states to be attributed to the DMN, and it was suggested to explain the inability to concentrate of some people. But this function does not seem very handy… why would our brain have such a disadvantageous tendency? To merely wander away… For what? Let’s think it through. Where do our minds go when we distract away from the present environment? When we are waiting at the bus stop or we space out from our book our mental life may result in some of the following states: a past experience pops out; a new idea for a project comes in; we give thought to a future plan, for example, a reminder to ourselves to look for train tickets or figuring out what to eat that day for lunch. This is what the DMN allows. We might say, then, that our DMN-distraction is not entirely useless.
This is what many investigations are trying to puzzle: what is it about the DMN that is useful for us. It’s been detected in situations where we engage in thoughts related to ourselves: our past (autobiographic memory), our present (spontaneous thoughts), and our future (prospective thinking, mental simulation, planning, etc.). Now let’s take a simple task and see whether and when these processes intervene. We are going grocery shopping. Yes, we need to be aware of external stimuli to do it right. We need to attend to the automatic opening of the doors, the location of our desired products, whether there are other people in the way, and so on. But we also need to recall where the products are — we don’t want to find them one by one all over the supermarket — and also why we want the ones we want — we’ve probably tried several of a kind and we are now picky about what we buy. So first, all of this triggers our autobiographic memory, the memory of our past experiences. Second, while we shop spontaneous thoughts may be triggered. “Ah! I needed to buy toilet paper! Good thing I remembered!” Thanks to that we got it off the list. And third, we are shopping for the whole week and we want to eat on the healthy side. This essentially needs some planning: what meals we plan on eating, what ingredients are part of them, what can go bad earlier than later, etc. All of these thoughts need simulation, planning and prospective thinking. It turns out that all of these “distractive” psychological processes are actually quite important to everyday tasks. When we space out of the environment we might be doing something useful after all.
So to answer the first question: Yes, there is some kind of intrinsic activity of the brain. Not everything fits into a stimulus-response conception of our behavior. The brain has a “wandering” Default Mode which does not necessarily hinder our thinking — even if sometimes entails distraction. Many times it is the opposite, it helps us in being more efficient and rational. The “Default Mode” of our brain underlies a state of mind which is to wander within and about our lives, our ideas, our plans, our needs… to wander about ourselves in a unified and purposeful way. One might say the DMN supports us in being period. In being our own, unique and particular selves.
