Two brain networks, two jobs
The default mode network is a set of brain regions that becomes active when you are not focused on a task — daydreaming, replaying a conversation, planning dinner. The salience network acts more like a spotlight operator: it flags what matters right now and helps you shift attention toward it. Awareness of mind wandering has been linked to activation in the salience network, which fits the idea that this network is what notices your attention has drifted [1].
If mindfulness training strengthens the connection between these two networks, the plausible story is that the salience network gets better at catching the default mode network in the act of wandering — and that catching is what lets you return to the breath or the task. That is a hypothesis about function, not something these studies demonstrate.
What a month of practice seems to change
In a study of 46 meditation-naive adults, 31 days of mindfulness meditation training increased functional connectivity between nodes of the default mode network and nodes of the salience network, compared with an active control intervention [2]. The same study found increased connectivity between the salience network and key regions of the central executive network, the third member of what researchers call the triple network [2].
A meta-analysis pooling twelve studies — 226 people in mindfulness training and 204 controls — reached a compatible conclusion: training produced significantly greater resting-state connectivity between the left middle cingulate, a salience network hub, and the posterior cingulate cortex, a central node of the default mode network [4]. The effect size was modest, and the authors describe it as evidence that training targets cross-network connectivity implicated in flexible control of internally oriented attention [4].
One caution about scope: these are resting-state scans, taken while people lie still and do nothing in particular. They show that the networks talk to each other more after training, not that people's minds wandered less during the scan or in daily life.
Mindful attention and mind-wandering look different in the scanner
The study that comes closest to your question compared three conditions in 59 healthy participants who had practiced mindfulness and mind-wandering: focusing on the physical sensations of breathing, letting thoughts connect freely, and simply resting [3]. Using a modeling technique that estimates which network drives which, the researchers found that the salience network and central executive network interacted differently depending on whether people were being mindful or letting their minds wander [3].
Compared with resting, mindfulness increased effective connectivity from the left central executive network to the salience network by way of the default mode network, while mind-wandering increased effective connectivity from the default mode network to the right central executive network [3]. In plain terms, the direction of traffic through these networks differed between the two mental states. This is a comparison of states within a session, not a demonstration that training reduces wandering over time.
Why the link to less mind wandering is still unproven
The intervention studies that measured connectivity did not measure mind wandering, so the two halves of the question have never been tested together in the same dataset [1][2][4]. A study that tracked both — connectivity before and after training alongside a validated measure of wandering — would be needed to say whether the brain change tracks the behavioral one.
There is also a conceptual wrinkle. The meta-analysis frames stronger default mode–salience connectivity as supporting flexible control of internally oriented attention [4], which could mean better monitoring of wandering rather than less wandering overall. A mind that notices its own drift more quickly may still drift; it just recovers sooner. Until a study measures both, the honest answer is that the connectivity effect is real and reasonably consistent, while its connection to reduced mind wandering remains a plausible but untested inference.
Sources used in this answer
Mindfulness is associated with intrinsic functional connectivity between default mode and salience networks
Awareness of mind wandering has been linked to activation in the salience network, and the paper examines the relationship between mindfulness practice and intrinsic connectivity between the default mode and salience networks, though it does not evaluate changes in mind wandering.
Mindfulness meditation increases default mode, salience, and central executive network connectivity
Thirty-one days of mindfulness meditation training in 46 meditation-naive adults increased resting-state functional connectivity between default mode and salience network nodes, and between the salience network and central executive network, compared with an active control.
Spectral dynamic causal modeling of mindfulness, mind-wandering, and resting-state in the triple network using fMRI
Comparing mindfulness, mind-wandering, and resting states, mindfulness increased effective connectivity from the left central executive network to the salience network via the default mode network, whereas mind-wandering increased effective connectivity from the default mode network to the right central executive network.
Disrupting The Resting State: Meta-Analytic Evidence That Mindfulness Training Alters Default Mode Network Connectivity
A meta-analysis of twelve studies found significantly greater resting-state connectivity after mindfulness training between the left middle cingulate (a salience network hub) and the posterior cingulate cortex (a default mode network hub), with a modest effect size.
Meta-analytic evidence that mindfulness training alters resting state default mode network connectivity
A meta-analysis of twelve studies reported significantly greater resting-state connectivity after mindfulness training between the left middle cingulate in the salience network and the posterior cingulate cortex in the default mode network, interpreted as targeting internetwork connectivity for flexible control of internally oriented attention.