Here's What We Know About the Science of Stammering

We know that there is a biologic basis to the disorder that is stammering and that it goes beyond the affected person’s control.

One just needs to watch a Lalu Yadav or a Bill Clinton enthral the masses to understand how critical speech fluency is for public success. But is speech fluency – or a lack of it – an innate trait or a result of environmental influences? Can it be improved by practice? And how far has the science come when it comes to understanding the associated dysfluencies?

The most well-known speech fluency disorder is stammering, also called stuttering. It affects about 70 million persons worldwide. There is an approximately 5% chance that any child will have stammering at some point growing up. Fortunately, about 75% of them outgrow it, some within months of onset, other after years.

There have been some high-profile cases over the years, including that of George VI, his life and miseries made even more famous by the Academy-Award-winning film The King’s Speech (2010). Closer to home, the Bollywood actor Hritik Roshan has talked of how he went through speech therapy to overcome stammering. The cricketer Dilip Vengsarkar is believed to have the disorder, though he has never talked about it himself.

Therapies and assistive devices do help improve stammering but not in all cases. The factors that lead to the frequent and spontaneous remission are unknown. In fact, we don’t know the exact cause of stammering itself.

Fortunately, we are making progress towards a full mechanistic understanding of this problem with help of functional neuroimaging. They assess brain function rather than its structure. Different modalities of functional neuroimaging have been used over the last two decades to study stammering. Some examples include:

  • Functional magnetic resonance imaging (fMRI), which measures blood flow to assess activity in various brain regions
  • Fludeoxyglucose positron emission tomography (FDG-PET), which uses an exogenously introduced tracer to assess glucose uptake
  • Functional near-infrared spectroscopy (fNIRS), which measures haemoglobin levels in the brain;
  • Magnetoencephalography (MEG), which quantifies magnetic activity produced by naturally occurring electrical brain activity
  • Proton chemical shift imaging, which measures the activity of various chemicals in the brain, and
  • Diffusion tensor imaging (DTI), which assesses how water molecules diffuse in the brain

The evidence from these studies has pointed to disturbances in widespread brain regions and circuitry in persons with stammering. The findings are thought to be secondary to a combination of innate traits, environmental influences and compensatory phenomena.

The areas particularly implicated include those that are involved in speech production and in the regulation of attention and emotion. An MRI study that I was involved in utilised a technique called pulsed arterial spin labelling – quantifying blood flow by magnetically labelling protons in blood – to document reduced blood flow to the brain’s language loop. The language loop is involved in various stages of speech production, including auditory comprehension, phonological and syntactic processing, lexical retrieval and speech motor planning, programming and execution. The study was published in December 2016.

The blood flow was particularly decreased in the Broca’s region, a part of the language loop and key to expressive speech. This study also noted an inverse correlation between the severity of stammering and the amount of blood flow in children and adults. Thus, it raised the possibility of this being is a trait-like vulnerability

The key to developing effective treatment modalities for any disorder is to conclusively identify the causes. We are not quite there yet but slowly inching closer. More importantly, we have enough visual evidence from functional imaging studies to bust various myths related to stammering. We know that it is a brain disorder, not a case of ‘psychological meekness’. We know that it is not simply due to stress or the result of a ‘weak personality’. Finally, we know that there is a biologic basis to the disorder that goes beyond the affected person’s control.

Jay Desai is a neurologist. He tweets at @southgujarati.