Have you ever noticed that your healthiest routines are often the first things to disappear when life becomes especially demanding?
You may exercise consistently for weeks until work becomes overwhelming. You may have a good evening routine until family stress rises. You may know exactly what you want to eat or what would help you feel better, yet find yourself reverting to whatever is easiest and most familiar.
It can feel frustrating because your intentions haven’t necessarily changed.
What has changed is the environment in which your brain is being asked to carry them out.
Last week, I introduced the idea that motivation and capacity are not the same thing. You can genuinely want to make a change without having the same resources available to sustain it at every moment.
Stress helps explain why.
Healthy Habits Require More Brainpower Than We Realize
We often talk about habits as though healthy behavior should eventually become effortless. Some behaviors do become more automatic with repetition, but changing and maintaining a behavior still requires cognitive work—especially when circumstances change.
Think about what may be required simply to follow through on an intention to exercise after work. You have to remember the plan, keep it important enough that other demands don’t displace it, stop what you are doing, resist the easier option, and adapt if the original plan no longer works.
That involves several functions associated with the prefrontal cortex, including:
- working memory
- attention
- planning and decision-making
- cognitive flexibility
- inhibitory control
These are some of the very abilities that can become more vulnerable under significant stress.
How Stress Changes the Brain
Neuroscientist Dr. Amy Arnsten has spent decades studying how stress affects the prefrontal cortex.
The prefrontal cortex supports many of our most sophisticated abilities: holding information in mind, regulating attention, considering consequences, inhibiting responses, adjusting strategies, and organizing behavior around future goals.
But it is also particularly sensitive to stress.
Under psychological stress, chemical signaling in the brain changes. Higher levels of stress-related catecholamines such as norepinephrine and dopamine can weaken the functioning of prefrontal networks while increasing the influence of faster, more reactive brain systems.
That shift can be useful in an immediate threat, when reacting quickly may matter more than carefully weighing several options. But the same shift is less helpful when the challenge is an ordinary demanding day and you are trying to exercise, prepare a healthy dinner, manage family responsibilities, and get to bed on time.
Under greater stress, the brain may become better prepared to react while becoming temporarily less effective at some of the functions required to reflect, plan, inhibit, and adapt.
Why This Matters for Behavior Change
Consider what intentional behavior change asks us to do. We need to hold a goal in mind, focus despite competing demands, make decisions, interrupt automatic responses, adjust when circumstances change, and return to the intention after disruption.
These are not abstract mental skills. They are part of the machinery that allows us to translate intention into action.
So when someone says: “I know what I need to do. Why am I not doing it?”
One possible explanation is that the cognitive functions required to carry out that intention are working under greater load. That does not mean stress eliminates choice or makes healthy behavior impossible, but that the effort required to make an intentional choice may increase.
Research Spotlight
In a major review published in Nature Reviews Neuroscience, Arnsten examined evidence showing that even relatively mild uncontrollable stress can impair prefrontal cognitive abilities.
The research helps explain why, during stressful periods, we may find it harder to sustain attention, inhibit an automatic response, plan ahead, or flexibly adjust our behavior. It also gives us a different way to understand something many people experience:
When life becomes more demanding, we often stop doing what we intended to do and start doing what is easiest or most familiar.
We may eat whatever is readily available, skip the workout, stay at the computer longer than planned, scroll instead of going to sleep, or return to patterns we thought we had already changed.
From the outside, this can look like a motivation problem.
From the inside, it may simply feel like, I just don’t have it in me today.
A Different Question to Ask
This distinction matters because the solution to a motivation problem and the solution to an overloaded system are not necessarily the same. Sometimes we do need greater commitment, clearer priorities, or more accountability. But sometimes applying more pressure simply adds another demand to a system that is already working hard.
A more useful question may be: “What is this behavior asking of me when I’m under stress?”
Does it require planning? Remembering? Making several decisions? Resisting an automatic response? Adjusting when things do not go as expected?
When we understand the demands behind a behavior, we can begin to see why something that feels relatively easy during a calmer week can suddenly feel much harder when stress rises. That perspective shifts us away from immediately assuming a lack of discipline. Instead, it invites curiosity about the conditions affecting our ability to follow through.
And that may be one of the most useful places to begin.
Reference
Arnsten, A. F. T. (2009). Stress signalling pathways that impair prefrontal cortex structure and function. Nature Reviews Neuroscience, 10(6), 410–422. https://doi.org/10.1038/nrn2648
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