The Default Mode Network

What it is

The discovery came from an observation rather than a hypothesis. Watching positron emission tomography scans, Raichle noticed that the resting brain of a patient between tasks was not dormant but busy, and that the busyness had a consistent shape. What had been treated as the baseline turned out to be a mode. The paper is Raichle and colleagues, A default mode of brain function, in the Proceedings of the National Academy of Sciences in 2001.

That much is solid. The network exists, it is one of the more reliably reproduced findings in human brain imaging, and it is associated with rest and with internally directed thought.

In effect

The reason the network matters outside imaging laboratories is the claim usually bolted onto it: that the default mode network is the mind-wandering network, and therefore that a life of continuous stimulation, which never lets the default mode come on, is suppressing a second form of attention rather than merely filling gaps in the first.

That is the argument Johann Hari makes in Stolen Focus, and it is a good one. It is also further than the evidence goes, and unusually the book says so itself. Hari states in his own prose, in the body rather than in the endnotes, that whether the default mode network is the mind-wandering network is an ongoing debate, with some scientists agreeing and others strongly disagreeing. That hedge deserves to be carried forward rather than quietly dropped.

The status of the debate is Hari's characterisation of what his interviewees told him. This page records that he reports an unsettled question. It records no verdict on who is winning, because the book does not supply one.

What it does not say

It does not say the network is the seat of mind-wandering. It may be associated with it, and the researchers disagree about whether it is the same thing, so an article may say the network exists, is well replicated and is associated with rest and internally directed thought, and may not say more.

It does not say internally directed thought is always restorative. Rumination runs on the same inward turn and is the cost side of it, which is one reason the simple story about protecting the default mode is too simple.

It does not say that filling every gap with stimulation has a measured neural consequence. That is the step the argument wants and the imaging evidence does not supply, and it belongs with the general caution about brain-imaging findings arriving in trade books with their qualifications removed.

This page describes a research finding and a dispute about its interpretation. It carries no clinical guidance.

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