WHY DOES EVERYTHING FEEL HARDER WHEN YOU’RE EXHAUSTED?

There is a particular kind of tired that makes a simple decision feel like a committee meeting. Which shirt? What should we make for dinner? Did I already answer that email? Where did I put the bottle? Why did I walk into this room?

And then there is the classic: “I know I know this. I just can’t access it right now.”

Sleep researchers have spent decades studying what happens to attention, memory, mood, and executive functioning when sleep is disrupted.

For mothers, the question becomes more complicated. Postpartum sleep loss isn’t usually one terrible night. It can be months of interrupted sleep layered on top of recovery from childbirth, hormonal changes, feeding, caregiving, work, and an entirely new level of responsibility.

SLEEP ISN’T JUST “REST”

Sleep supports a number of processes involved in everyday cognition and emotional functioning. During sleep, the brain is involved in processes related to memory consolidation, emotional regulation, and restoration of normal alertness.

That doesn’t mean one bad night destroys your ability to think. It means sleep is part of the infrastructure your brain uses to function.

When that infrastructure is repeatedly interrupted, the effects can show up in ways that feel surprisingly ordinary: difficulty concentrating, forgetfulness, slower thinking, irritability, lower frustration tolerance, and feeling overwhelmed by decisions that normally wouldn’t seem difficult.

THE RESEARCH ON MOTHERS IS MORE COMPLICATED THAN “SLEEP LOSS = MOM BRAIN”

One of the earliest prospective studies specifically examining postpartum women followed 30 first-time mothers and 28 nonpostpartum controls during the first three weeks after birth.

The postpartum women experienced more nighttime awakenings and more time awake after going to bed. Researchers found relatively few differences on their objective cognitive measures. But performance on memory and psychomotor tasks appeared to be influenced by sleep loss.

The researchers concluded that the women in the study adapted surprisingly well to the disruption, while still finding meaningful relationships between sleep indices, mood, and cognitive performance.

The research doesn’t say: “New mothers lose their brains.” It says something much more realistic: sleep disruption can matter, but the human brain is also remarkably adaptable.

THE BIGGER PICTURE

A 2026 systematic review looked across 33 studies involving 16,563 women during pregnancy and postpartum. The researchers found that poor sleep was consistently associated with difficulties in emotional functioning, including mood and emotion regulation.

Findings for specific cognitive functions—such as memory and cognitive inhibition—were much more mixed. If a study finds that poor sleep is associated with feeling more emotionally overwhelmed, that’s evidence. If another study finds no significant difference on a particular memory test, that’s evidence too.

Research doesn’t have to produce one dramatic answer to be useful. Sometimes the most accurate conclusion is: It depends on what you’re measuring.

SLEEP AND MENTAL HEALTH AREN’T A ONE-WAY STREET

Poor sleep can affect mood. But anxiety, depression, stress, and rumination can also make sleep worse. So the relationship can become circular.

Researchers studying postpartum sleep have repeatedly found relationships between poor sleep and emotional disturbance. But observational studies can’t always tell us which came first.

That’s why we should be cautious about statements like: “Sleep deprivation causes postpartum depression.” The research supports a relationship. It doesn’t justify pretending the relationship is simple.

THE MOTHER WHO IS “FINE”

One of the most interesting findings from early postpartum research is that mothers can appear to adapt. In the 1997 prospective study, new mothers reported substantial changes in their sleep patterns, but relatively few differences appeared on objective cognitive testing.

That doesn’t mean the sleep disruption didn’t matter. It means humans can compensate. And compensation isn’t the same thing as being unaffected.

You can function. You can go to work. You can pack lunches. You can answer emails. You can remember the pediatrician appointment. And still feel like your brain is operating with twelve tabs open and three of them are frozen.

WHAT ABOUT LONG-TERM BRAIN DAMAGE?

There is not enough evidence to tell mothers that ordinary postpartum sleep disruption permanently damages their brains. That would be a much stronger claim than the research supports.

The more defensible conclusion is that chronic or disrupted sleep can affect cognitive and emotional functioning, and that postpartum sleep deserves to be treated as a meaningful part of maternal health.

THE SLEEP PROBLEM ISN’T ALWAYS “GO TO BED EARLIER”

For a mother waking several times a night, telling her to “get more sleep” can be almost comically unhelpful. The problem may not be bedtime.

It may be an infant waking repeatedly, feeding, a partner’s work schedule, another child’s needs, postpartum discomfort, anxiety, household responsibilities, or simply the fact that there is no uninterrupted block of time available.

This is why researchers increasingly treat maternal sleep as something influenced by the entire family and social environment—not simply an individual’s bedtime habits.

A 2025 SYSTEMATIC REVIEW

A 2025 systematic review and meta-analysis examined 60 studies involving more than 20,000 postpartum participants. The review looked at postpartum sleep and sleep interventions in relation to outcomes including mental health and other maternal health outcomes.

The larger evidence base reinforces an important point: maternal sleep is not a trivial wellness issue. It is part of postpartum health.

SO WHY DOES “MOM BRAIN” FEEL SO REAL?

Because several things can be true at once. Sleep disruption can affect attention and mood. Motherhood can dramatically increase the number of things competing for your attention. Stress can make concentration harder. Anxiety can consume cognitive bandwidth. Hormonal and physiological changes can accompany the postpartum period.

Constantly switching between work, childcare, household management, and emotional responsibilities creates its own cognitive demands.

When a mother says, “I feel like my brain doesn’t work anymore,” the scientifically honest answer isn’t: “That’s just mom brain.” It’s: There are several plausible contributors—and sleep is one of the most important ones we can actually measure.

WHAT WE DON’T KNOW

The research still has important limitations. Studies use different definitions of poor sleep. Some rely on self-report. Others use actigraphy or objective sleep measures. Postpartum periods vary dramatically across studies.

Some studies focus on first-time mothers. Others include mothers with multiple children. And cognitive tests measure specific abilities—not the full complexity of everyday life.

A laboratory test might tell us something about working memory. It cannot fully capture what happens when you’re trying to remember a grocery list while answering a work message while someone is crying. That gap between laboratory cognition and lived motherhood is worth remembering.

WHAT THE RESEARCH SAYS

Poor sleep during the peripartum period is consistently associated with poorer emotional functioning. Evidence for specific cognitive effects is less consistent. That means we can confidently say sleep matters for maternal wellbeing without pretending science has completely explained “mom brain.”

RELATED RESEARCH AREAS

Mom Brain · Postpartum · Psychology · Maternal Health