The default brain network and ADD
So in the previous post I published some New Scientist articles about the ‘default network’ in the brain. This network kicks into action as soon as we stop focusing our attention on a task.
The default network is where we think. Imagine living like this:
People who suffer damage to their medial prefrontal cortex become listless and uncommunicative. One woman who recovered from a stroke in that area recalled inhabiting an empty mind, devoid of the wandering, stream-of-consciousness thoughts that most of us take for granted.
No default network, no thoughts.
The default network is aberrant in schizophrenia, and schizophrenic subjects appear to have problems accessing their default network properly.
In the healthy subjects, the default mode network resonated slowly and regularly as observed by blood flow. In the patients with schizophrenia, the activity in the brain increased and was significantly more irregular, although they performed equally well on the task. Brain’s ‘Default Mode’ Awry In Schizophrenia
Schizophrenia is interesting because it is treated with dopamine antagonists. No direct correlation can be found between schizophrenia and high dopamine levels, though high dopamine is known to cause delusions. However, some scientists believe schizophrenia may be an autoimmune condition in which autoantibodies trigger dopamine receptors in the brain. The fact is, dopamine antagonists control and treat delusions and hallucinations.
In Alzheimer’s, not only is there a loss of dopamine D2 receptors in the brain, but the default network areas specifically accumulate plaques. Alzheimer’s patients appear to turn on their default network when asked to concentrate on a task, while normal subjects turn off their default network.
In terms of neurotransmitters, at the direct opposite end of the spectrum from schizophrenia is attention deficit (hyperactivity) disorder. AD(H)D is considered a condition characterised by low dopamine levels. Low dopamine levels lead to a lack of attention – to daydreaming.
Whilst attention deficit is typically thought to be something that affects children, adults experience it too – though perhaps not so obviously, possibly because the default network is something that matures into a complex and cohesive network during one’s lifetime.
In recent years, the brain’s “default network,” a set of regions characterized by decreased neural activity during goal-oriented tasks, has generated a significant amount of interest, as well as controversy. Much of the discussion has focused on the relationship of these regions to a “default mode” of brain function. In early studies, investigators suggested that, the brain’s default mode supports “self-referential” or “introspective” mental activity. Subsequently, regions of the default network have been more specifically related to the “internal narrative,” the “autobiographical self,” “stimulus independent thought,” “mentalizing,” and most recently “self-projection.” However, the extant literature on the function of the default network is limited to adults, i.e., after the system has reached maturity. We hypothesized that further insight into the network’s functioning could be achieved by characterizing its development. In the current study, we used resting-state functional connectivity MRI (rs-fcMRI) to characterize the development of the brain’s default network. We found that the default regions are only sparsely functionally connected at early school age (7–9 years old); over development, these regions integrate into a cohesive, interconnected network. The maturing architecture of the brain’s default network
What is really fascinating about the default network to me, is that the more I read about it, the more it seems to be how my brain functions.
I’ve been so busy studying autism, perhaps I should have been paying more attention(!) to attention deficit disorder. I have always had ADD. It is the cause of many of my problems, but also the cause of a lot of my talents.
Since being a child I have been chided for being in a permanent daydream. My imagination is constantly in action. I frequently take on the look of the gormless because I disappear off onto my own planet, open-mouthed, as I speculate about some possible future, or some possible theory about the universe. I burn the dinner, I leave tasks half-finished for other tasks, I don’t pay attention to where I am going, I get lost in the supermarket and make six laps because I am too busy pondering the universe, and at any given second I can break off half way through a sentence or a line of code to go google whatever question pops into my head.
I have evolved a lot of coping mechanisms for these traits: I have an OCD level of strictness about making sure I have locked the door, I have thought about the items I need to buy, I have checked my keys are in my bag, I have looked both ways before crossing the road, and I have set the kitchen timer. I often have to make a conscious effort to switch off the wireless internet connection so I can get on with my writing. The OCD is not real: it is simply my conscious way of dealing with my short attention span.
Whilst most of the world may regard this as a disorder, I prefer to regard it as a difference.
When I am not on the failsafe diet (which is never), my attention deficit disorder is very serious indeed, to the point where it could be dangerous for me to drive a car (my driving instructor always chided me for not paying enough attention). Sometimes it has been so bad that I have felt I cannot be gainfully employed due to the time I waste doing everything except working. My brain buzzes, throws disjointed thoughts at me, and repeats itself again and again.
When I am on the failsafe diet, however, I think quite clearly. I can focus when I need to, but I still go off on massive reveries and have epiphanies about things. So what? What’s wrong with spending your time thinking? I’m sure Sir Isaac Newton wouldn’t have discovered all those laws of physics if he hadn’t spent so much time daydreaming.
My big theory about the default network is that it is suppressed by dopamine, and activated when dopamine is low. I’ve found a couple of studies that back up this theory, here and here. Indeed, this blog describes how the use of stimulants like ritalin deactivate the default network.
The default network is where my consciousness lives. I’ve tried meditation before and I find it tremendously difficult to switch off my stream of consciousness. I have no patience for meditation or yoga. Switching off is something that I can perhaps do when I am watching television or reading very intensely, where I just have words going in that I process without thinking about them, though it only lasts a few seconds before the stream of consciousness reasserts itself again.
I find it incredibly uncomfortable to try to switch off that stream of consciousness, like holding one’s breath. It seems to me that being asked to concentrate can make me irritable and tired.
Music is something I have a real problem with. I rarely listen to music. When in the right mood, I like listening to music, but it tends to take over my brain. If it is too loud (i.e. speaking volume), it actually interferes with my stream of consciousness. I find this very, very uncomfortable. If I’m forced to sit in a car and listen to music that is loud enough to interfere with my thoughts, it’s like torture, and I can get really irritable. It’s like I’m being forced to concentrate against my will.
So ADD is not so much a case of “I can’t concentrate,” it’s a case of my dopamine being low and as a result my default network is constantly reasserting itself over the rest of my mind. This is not an unpleasant experience, in fact, I prefer things that way.
The things that the default network is good at doing are the same things that I am good at doing, for example:
Planning: whether a route, or a future event. I always plan things. I am uncomfortable if I don’t plan things. It seems to me that when I get irritated by something, it is almost always because a plan has gone awry and my brain has to re-plan at short notice. I am very good at envisaging future scenarios, even totally unexpected ones. If a conversation is happening where future possibilities are being discussed, I can guarantee to have thought up each of the future possibilities long before someone else suggests them. When I listen to politics on the radio, I am frequently annoyed by the lack of foresight politicians have for the consequences of their policies. I’m an “I told you so,” kind of person. I like to think this trait makes me a good scientist, because when I observe a phenomenon, I can imagine many possible causes and therefore have many theories to suggest and test.
Remembering: particularly autobiographical memories. This elephant never forgets. I often recall scenarios to other people, only to find they have forgotten them. My memory is very reliable, and it’s very rare that I have forgotten something that someone else remembers. I am also a terrifying fact machine, as long as I can relate the facts to myself in some way.
Imagining: I write fantasy and science fiction. I share my big imagination with one grandparent in my family who used to tell us stories when we were kids. This grandparent also has ADHD and can’t sit still.
Moral decision making: I am a very principled, moral person with a complex set of standards that I adhere to. I don’t blindly follow rules however, I think about the consequences of actions and consider the greater good.
Self-awareness: things simply don’t get by me unnoticed the way they seem to get by other people. I always used to wonder why people didn’t understand obvious things about themselves. Now I guess I do know. They aren’t using their default networks as much as I am.
The default network also explains the things I am not very good at, for example – it answers that question I have been asking myself for years – why am I so slow at everything? How come it takes me twice as long to do any task as it takes someone else? How come on those silly facebook quizzes, I always take twice as many minutes to complete them as everyone else?
Though I have a big imagination, I’ve struggled to actually get on and do the process of writing for years and years. I have to go to some unusual extremes in order to write. I can’t concentrate during the day, if there is background noise, if there is anyone else around. I basically have to closet myself in a dark room in the dead of night in order to put down all my ideas on paper.
I see now that my default network is getting in the way, it’s reasserting itself all the time and slowing me down when I have to focus. It’s almost like a kind of epilepsy, I’m just switching off for a few seconds here and there all the time, my mind wandering without me even being aware of it.
Do other people experience conciousness differently to me? When they are concentrating on a task, do they simply stop thinking? I can’t imagine what that feels like.
There is one major anomaly though. According to this (free) review of the studies done on the default network so far, the default network is activated during theory of the mind tasks. Considering how commonly autism and attention deficit disorder occur together in the same individual, this is very odd.
Regarding the function of the default network in autism, the review implies mixed results so far, with some studies suggesting increased brain volume in default network areas, whilst others suggesting absence of activity during passive tasks when the mind would usually wander. This suggests the autistics in question were concentrating very hard on the task they were given! Still other information in the review points out to a complex interaction with the amygdala, which is known to contribute to social cognition, and interacts with the default network.
An intriguing possibility suggested by the authors of the study […] is that the failure to modulate the default network in ASD is driven by differential cognitive mentation during rest, specifically a lack of self-referential processing […] Another recent study using analysis of intrinsic functional correlations showed that the default network correlations were weaker in ASD (Cherkassky et al. 2006). Of note, the individuals with ASD showed differences in a fronto-parietal network that has been recently hypothesized to control interactions between the default network and brain systems linked to external attention (Vincent et al. 2007b). These data in ASD suggest an interesting possibility: the default network may be largely intact in ASD but under utilized perhaps because of a dysfunction in control systems that regulate its use. The Brain’s Default Network
Now I’m the first to point out I’m not a typical aspie. Many other aspies seem a lot whackier than me (higher dopamine?), and as far as the theory of the mind goes, I do pretty good (but then, I’m female). I’ve never fitted the Baron-Cohen “extreme male brain” theory. I’m rubbish at maths, but great at logic, pattern-spotting and programming.
However, I’m not alone in being anomalous. Fifty to sixty percent of autistics also qualify for a diagnosis of ADD/ADHD, see this reference. Yet autism can also occur together with schizophrenia, as can schizophrenia and ADHD occur together.
So what’s going on here?