The Biology and Reality of Stammering: A Personal and Scientific Perspective

What is a stammer/stutter?

We all stumble over words from time to time, but for someone with a stammer this isn’t due to confusion or just having a bad day. Stammering is a speech and language disability characterised by difficulty vocalising speech due to differences in the brain’s ability to plan and produce it (Byrd et al. 2024).

Stammering is most commonly developmental, usually arising in young children, although it can also begin in older children or during adulthood. Brain injuries, such as stroke or trauma, can also trigger a stammer, and this may be temporary or can persist into adulthood.

In any case, having a stammer can be debilitating; having no easy way to communicate ideas and thoughts is a uniquely isolating experience. For this reason, people with a stammer are more likely to present with social anxiety, have negative attitudes towards communication, impaired social skills and maladaptive compensatory behaviours (Bernard et al. 2022; Tichenor et al. 2023). However, there is considerable variability in how stammers present within individuals. Therefore, understanding the neurobiology of stammering, and how to support people with a stammer, is not without its challenges.

Genetics

Overall, it is accepted that stammering is likely to be driven by a combination of genetic and environmental factors. Understanding how genes influence stammering could also further our understanding of how the brain produces fluent speech - a mysterious trait common to only a handful of species.

50% of stammerers can identify at least one relative who also stammers, suggesting there is a heritable aspect (Boyce et al. 2022). Some genome studies have found that genetic factors may influence an individual’s risk of developing a stammer, and there are also potential associations with other conditions such as autism spectrum disorder and depression (Polikowsky et al. 2025). However, other genome and neuroimaging studies have provided no further insight (Polikowsky et al. 2022). 

There is also a sex disparity in the prevalence of stammering, with twice as many males presenting with a stammer in childhood compared to females. Additionally, males are more likely to have a stammer which persists to adulthood, with a 4:1 male:female ratio in the adult stammering population (Yairi et al. 2013). However, the mechanisms driving this sex difference are not understood.

The vocal motor system

It has been established that stammering has no association with cognition or intelligence and is instead a vocal-motor condition, characterised by impaired neural speech processing (O’Brien and Onslow, 2011). Stammering is not believed to be due to brain atrophy, or gross changes to brain structure, although more subtle variations have been reported in the basal ganglia, pre/motor cortices, and inferior frontal gyrus (Bakhtiar et al. 2025; Gracco et al. 2022). 

On a cellular scale, several mechanisms have been associated with stammering, notably energy supply. Disrupted energy supply to neurones has been proposed to contribute to stammering, with electroencephalogram (EEG) studies consistently reporting lower beta power compared to non-stammerers. Beta power is associated with cognitive engagement and neurone firing, and in turn more energy-intensive brain activity (Nofzinger et al. 2000), therefore reduced beta suggests reduced neuronal metabolism may be a core characteristic of stammering.

Additionally, intracellular signalling genes, such as lysosomal targeting pathways, are associated with increased stammering risk (Srikumari et al. 2020). Lysosomes are organelles which contain enzymes involved in degrading and recycling products to maintain cellular health and function. Disruption to these pathways may impede lysosomal enzyme function, in turn lowering the rate of recycling products and impairing energy supply to neurones (Alm et al. 2021). 

Another mechanism  which could affect energy supply in stuttering individuals is impaired glycolysis (the breakdown of glucose to produce energy). The ARNT (Aryl Hydrocarbon Receptor Nuclear Translocator) gene, associated with adaptation to low oxygen levels, activation of glycolysis and lactate production for energy, has been associated with stammering (Kraft et al. 2010). This could potentially contribute to a neuronal energy deficit, a phenomenon already studied in autism spectrum disorder (Di Napoli et al. 2015). 

Another area of interest in the cellular mechanisms driving stammering is dopamine signalling. Since the 1990s, increased presynaptic dopamine activity has been suggested to contribute to stammering, since termed the ‘dopamine hypothesis’ (Wu et al. 1997). The dopamine hypothesis has been supported by genetic studies which demonstrate upregulation of dopamine-associated genes (Hirvonen et al. 2004; Lan et al. 2009). However, blood plasma levels of peripheral dopamine and its breakdown metabolites have been reported to display no significant differences between stammering and non-stammering individuals (Mohammadi et al. 2018; Rastatter and Harr, 1988). 

Antipsychotic drugs which reduce dopaminergic signalling, such as haloperidol and risperidone, have been reported to reduce stammering symptoms, further supporting the theory that heightened dopamine activity could contribute to stammering (Burns et al. 1978; Maguire et al. 2000). However, the involvement of dopamine pathways remains under debate, as these antipsychotics also target cholinergic pathways, which may be an alternative mechanism to modulate stammering symptoms. The influence of a hyperdopaminergic state in stammerers has not yet been  thoroughly described - if it is even a consistent characteristic across the population at all - but does support that altered energy supply and neurone function could contribute to the development of stammering.

Can pharmaceutical intervention provide benefit?

Treatment with risperidone, a dopamine receptor 2/serotonin receptor 2 antagonist, has resulted in significant reduction of stammering severity compared to a placebo group (Maguire et al. 2000). More recently, the action of risperidone has been proposed to manage dopamine elevation and rescue the hypometabolic state in stammering brains, but may act via astrocytes as well as neurones, opening a further avenue which may contribute to the interplay between dopamine signalling, energy supply and stammering (Maguire et al. 2021). Conversely, other studies have reported dose-dependent induction of stammering symptoms upon treatment with risperidone in non-stammerers (Atay et al. 2014; Yadav et al. 2010), so the overall picture is unclear. 

One proposed reason is the dual action of risperidone on dopaminergic and serotonergic pathways. On one hand, if risperidone reduces activity of a hyperdopaminergic state, as reported in stammering, this may reduce symptoms. Conversely, serotonin-induced stammering could occur via serotonin’s inhibition of the nigrostriatal dopamine pathway, potentially disrupting movement control to induce stammering symptoms in non-stammerers (Ekhart et al. 2021). Additionally, the effect of dopamine on stammering may not be linear, with too little dopamine or too much resulting in disordered speech (Cools and D’Esposito 2013). 

Pharmaceutical therapies would surely improve the quality of life for people with severe stammering and muteness. However, whether pharmaceutical intervention is beneficial for all stammers is controversial. Once more, ‘fixing’ a condition which is not harmful or progressive may not provide benefit to all individuals; merely alleviating symptoms may not change the mindset around the stammer itself. 

My own experience

As someone with a stammer, I can say that it changes your perception of many things in daily life. My stammer developed around 11-12 years old, and I remember how I gradually started to lose my fluent speech, preventing me from doing things that had previously been helping to build my confidence, social skills and development. As a young teenager starting secondary school, trying to figure out their identity and integrate into their social circles, it is a challenging time for most. As I was losing the ability to speak, socialise, and participate in things I had when I was younger, I felt I was losing a sense of myself in the process. Without the knowledge of what a stammer was, what was happening to me became increasingly unnerving. Ultimately, as I became a young teenager, my stammer was becoming progressively more difficult to manage and I felt there were more reasons to go into my shell than there were to come out of it, and my confidence and sense of identity were diminishing. After a particularly bad day at school, I went home and finally admitted that I couldn’t do this alone anymore and I wanted to be referred for speech therapy. 

Speech and Language therapy

There is no cure for a stammer, but some benefit can be obtained from speech therapy. 

Fluency shaping methods focus on minimising or modifying the stammering to reduce its severity. Such techniques include breath control, pausing, or changing pronunciation of words or syllables to ease speech and reduce frequency or length of stammering (Esfandeh et al. 2025; Gupta et al. 2022). This idea suggests that if stammering events are minimised, an individual can avoid communication impairment and, in turn, experience a better quality of life with reduced internalised stereotyping (Neef et al. 2024). From a neurobiological perspective, there is considerable supporting evidence that fluency therapy can help the brain compensate for deficits in processing networks (De Nil et al. 2001; Korzeczek et al. 2021; Neef et al. 2022). 

A strange phenomenon which can dramatically reduce the frequency of stammering is singing (Healey et al. 1976). One potential reason for this is that the larynx, the voice box, is controlled by separate neural pathways when we talk versus when we sing, due to the different laryngeal functions involved in both actions (Harris et al. 2023). Studies indicate the ventral laryngeal motor cortex in the brain, which may contribute to stammering during normal speech, may be less engaged during singing (Neef et al. 2021; Neef et al. 2024). Conversely, the dorsal laryngeal motor cortex may compensate by increasing connections, leading to no significant alterations in stammerers compared to non-stammerers. If the dorsal laryngeal motor cortex is engaged more in singing, this change in coordination of larynx function may contribute to increased fluency during singing, as opposed to speech (Garnett et al. 2018; Korzeczek et al. 2021).

Fluency shaping methods have symptomatic benefits (Frigerio-Domingues et al 2019; Irani et al. 2012; Neef et al. 2022), but do not challenge another, potentially greater, question. Is stammering actually a problem? Additionally, as has been discussed regarding treatments for autism spectrum disorder (Milton et al. 2012), merely minimising symptoms of a condition may not provide needed psychological and emotional support. In the process of encouraging a person to hide or avoid their stammer, the therapy may convey the idea that a stammer is a problem to fix, rather than an innocuous variability within the population that possesses no harm or danger. 

Alternative methods aim to build confidence around the stammer, reducing fear and anxiety, often through incorporating psychological and cognitive behavioural therapy techniques (Gupta et al. 2022). This approach aims to deter focus from stammering symptoms towards more general communication skills, in turn supporting integration into society and encouraging people to socialise and communicate alongside their stammer, rather than against it. Fluency shaping is a popular method, and is particularly beneficial for young children who do not seem to experience the emotional weight of their stammer as severely and whose stammer can often be completely resolved. However, cognitive behavioural therapy is a popular method to support older children and adults who are more likely to experience psychological and emotional aspects of the condition, with increasing evidence indicating young children can also benefit from this therapy approach (Menzies et al. 2009; Toğluk et al. 2026). 

Speech therapy is continuously evolving, more recently incorporating technology such as tele-rehabilitation to reduce cost and increase access to treatment, and mobile apps to help people practise techniques at home (Almudhi 2021; Lewis et al. 2008; Mod Fadzilah and Arshad 2017). The constant discussion within the field around the needs of patients, neurobiological mechanisms, therapeutic approaches and societal education to support people affected by stammering are constantly highlighting further opportunities to help people with stammers make their voice heard.

Awareness

When my speech therapist asked why I was afraid of my stammer, or why I thought it was a bad thing, my answers rarely came from myself. They were driven by other people’s responses and behaviour. If I thought someone judged me, laughed at me or conversely pitied me as if I was broken, this was usually due to their lack of understanding and education. Often, if people are receptive, all it takes is one conversation to clear things up; the difficulty arises when no one is talking (yes, I see the irony in that statement). 

The stammer is usually not the core issue, the reaction to the stammer is, which is why awareness, understanding and support matters so much. These things are the difference between a fulfilling and enriching life for someone with a stammer, or judgement and isolation. 

If you would like to know more about living with a stammer, and how workplaces, schools, and society can support people with stammers, please look at the following links:

1. https://speechandlanguage.org.uk/ - UK organisation supporting young people with speech and language disorders

2. https://stamma.org/ - UK charity campaigning for support and awareness around stammering

3. https://www.aafp.org/pubs/afp/issues/2019/1101/p556.html - awareness in the workplace, schools etc. to help support people.

4. https://stamma.org/about-stammering/influential-people-who-stammer - summary of well-known and influential people who stammer, and their perspectives

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This article was written by Daisy Stringfellow and edited by Rebecca Pope, with graphics produced by Ishika Joshi. If you enjoyed this article, be the first to be notified about new posts by signing up to become a WiNUK member (top right of this page)! Interested in writing for WiNUK yourself? Contact us through the blog page and the editors will be in touch.