Resting-State Functional Connectivity

What it is

Two brain regions are functionally connected, in this sense, when their activity varies together over time. The measure says nothing about wiring. It records a statistical relationship: when one region is more active than usual, the other tends to be as well, or, in the case of a negative relationship, tends to be less active.

Doing this at rest means collecting scans while no task is set and asking which regions move together. The question the 2003 paper put was whether the default mode is a real, coherent network. Brain imaging studies had found that regions such as the posterior cingulate cortex and the ventral anterior cingulate cortex were more active at rest than during demanding cognitive tasks. That pattern could have been a scatter of unrelated decreases. Connectivity at rest was a way to test whether the regions belonged together.

The authors framed three questions: whether the resting-state network exists, whether it is altered by simple sensory processing, and how cognitive processing changes it. They presented their paper as the first resting-state connectivity analysis of the default mode, and as strong evidence for a cohesive default mode network.

In effect

The design started from two regions that were less active during a working-memory task, the posterior cingulate cortex and the ventral anterior cingulate cortex. The authors then measured how those regions were connected at rest.

The posterior cingulate was strongly linked with the ventral anterior cingulate and with other regions associated with the default mode network. A visual processing task produced connectivity patterns nearly identical to those at rest, so a simple sensory task did not break up the network.

The third result ran the other way. Three lateral prefrontal regions that were more active during the working-memory task showed significant negative correlations with the posterior cingulate at rest. The authors suggested that prefrontal activity may suppress default mode activity during cognitive work. That is their interpretation of a correlation, and the paper's own wording is a suggestion.

Taken together with the earlier oxygen-extraction work, the connectivity result gave the default mode a second line of support. The regions fell away from baseline during goal-directed tasks, and they were coupled with one another whether or not a task was running. That second point is the reply the network's defenders give to the objection that the default mode needs a special rest condition to exist.

What it does not say

It does not show that the regions are anatomically connected to one another, or that one drives the other. Correlation at rest is a statistical relationship.

It does not show what the network is doing. The paper establishes that the network is coherent and that prefrontal regions move against it. The function of the network is a separate question, taken up in later thought-sampling work.

It does not resolve the objection that resting-state observations have no privileged status as a measure of brain function. That objection concerns the interpretation of resting-state studies in general, and this concept sits at the centre of it.

This page describes a research method and a finding. It carries no clinical guidance.

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