Mum brain: is it real, how long does it last, and what actually happens

I need to tell you about the walk.

The walk that made me want to dissolve into the pavement, cancel all social obligations indefinitely, and never open my mouth in public again.

The walk. Three months postpartum.

I had my baby strapped to my chest in a wrap. One of those wraps that, in theory, takes forty-five seconds and, in practice, requires a YouTube tutorial and a small ceremony. We were on a “catch-up walk” with a friend. A friend who arrived looking glossy-haired, fresh-faced, and entirely like a person who had slept recently. She was wonderful. I was, technically, upright.

And then she asked me something. Something normal. Something conversational. The kind of question I would have answered effortlessly six months before, on any given Tuesday, probably while multitasking.

I opened my mouth.

And I had an out-of-body experience. I could literally see myself from slightly above. Baby in wrap, muslin draped over one shoulder, and I was cringing at every single sentence that came out of my own mouth. I was mumbling. I was circling. I started a thought and lost it halfway through. I reached for a word, a perfectly ordinary word, the kind I had used ten thousand times and it simply was not there. Gone. I watched myself fill the gap with a vague hand gesture and a noise that was not quite a word.

My God, I thought, watching myself from above. How have I become so ineloquent?

I walked home. I replayed every sentence. I spiralled quietly. And I made myself a solemn, slightly unhinged vow. I was going to become a hermit. No more social contact until further notice. Possibly ever.

If you are a mother, especially if you are a high-performing woman who has spent years being sharply articulate, quick-witted, and the person in the room who always has the right word, you know exactly what I am talking about. Not just forgetting where you put your keys. The deeper, more destabilising thing. The sense that your mind, your actual mind, has been replaced with something warm and formless.

Scientists have a name for it. And when I learned what was really happening, everything changed.

Why does nobody tell you about matrescence?

Matrescence is the process of becoming a mother. That is the simple version. The fuller version is this. It is one of the most significant neurological, psychological, hormonal, and identity-level transitions a human being can undergo, and it has been largely invisible in mainstream culture for fifty years.

The term was coined in 1973 by medical anthropologist Dana Raphael, the same woman who gave us the word “doula.” It describes a transformation as fundamental as adolescence. The same scale of brain rewiring, hormonal upheaval, and identity restructuring that we readily excuse in teenagers, happening to adult women, with essentially no cultural acknowledgement and even less support.

“Everyone knows adolescents are uncomfortable and awkward because they are going through extreme mental and bodily changes. But when they have a baby, women are expected to transition with ease. To breeze into a completely new self at one of the most perilous and sensitive times in the life course.”

Lucy Jones, Matrescence (2023)

Sixty-seven per cent of mothers have never heard the word matrescence. Which means millions of women are going through one of the most significant transitions of their lives without the language to name it, and, as a consequence, pathologising an entirely normal developmental experience as personal failure.

The fuzzy brain. The lost words. The out-of-body cringe on a walk with a friend. These are not signs that something has gone wrong. They are signs that something enormous is happening.

The goo stage. You are mid-metamorphosis.

Researchers and developmental psychologists have started describing the postpartum period as a liminal “mush” or goo stage. A chrysalis moment in which you are neither completely the person you were before, nor yet settled into the person you are becoming.

You are, in the most accurate and scientifically grounded sense, mid-metamorphosis. And metamorphosis, as any caterpillar could tell you, is not tidy. Inside the cocoon, the caterpillar does not neatly reorganise. It dissolves. It becomes liquid. And from that goo, something entirely new assembles itself.

The postpartum brain fog, the mum brain, the mumnesia, the lost words on a perfectly ordinary walk. These are the goo. This is what reorganisation feels like from the inside.

The neuroscience of postpartum brain fog

In 2017, neuroscientist Dr Elseline Hoekzema and her team published landmark research in Nature Neuroscience demonstrating for the first time that pregnancy causes significant, measurable, long-lasting changes to grey matter in the maternal brain. Specifically in regions governing social cognition, empathy, and threat detection. These changes persisted for at least two years postpartum. The researchers found that the brain was not deteriorating. It was specialising. Pruning and reorganising with extraordinary precision.^[1]

A 2023 review in Trends in Cognitive Sciences further established that matrescence represents a distinct window of large-scale neurological reorganisation. The same kind of restructuring last seen in early childhood and adolescence, with long-term consequences that persist across the lifespan.^[2]

What gets temporarily crowded out during this reorganisation? Verbal fluency. Word retrieval. The rapid-fire, linear thinking that served you so well before. These are the functions that surface as brain fog, mumnesia, the lost words on the walk. They are not signs of decline. They are signs of the brain redirecting resources while it restructures.

This is not you losing your edge. This is your edge being relocated. And the relocation, by its nature, is loudest while it is happening.

Why it hits high-performing women differently

Here is what I have come to understand about that walk, and about the vow I made at the end of it.

For women who have built a significant part of their identity on being sharp, articulate, quick, capable, the person in the room who always has the words, postpartum brain fog is not just inconvenient. It is identity-destabilising in a way that goes far deeper than ordinary forgetfulness.

Because it is not just the words that are temporarily gone. It is the version of yourself that you have relied on. The version that felt competent, coherent, and in command of a room. The version that would never have been caught mumbling on a walk, watching herself from above and cringing.

Reproductive psychiatrist Dr Alexandra Sacks describes matrescence as a time of profound ambivalence. The simultaneous experience of expansion and loss.^[3] And she argues that without language for it, women pathologise normal developmental experience. They believe something is wrong with them when something is, in fact, deeply and powerfully right.

The loss of the sharp, eloquent, high-performing self, even temporarily, even in service of something extraordinary, is real grief. And it deserves to be named as grief. Not dismissed as baby brain. Not resolved by becoming a hermit.

What I know now that I did not know on that walk

Matrescence is not a phase you get through and emerge from unchanged, back to who you were. It is not a pause. It is not a detour. It is a permanent, irreversible, neurologically documented expansion of who you are. And the goo stage is simply the middle of it. The part that is loudest and most disorienting, because that is when the most significant restructuring is happening.

So if you are three months postpartum, baby in a wrap, cringing at yourself in a park, then I see you. I was you. And I want you to know. You are not losing your mind. You are mid-metamorphosis. You are in the goo.

And the goo, it turns out, is where extraordinary things are built.