Stuttering, estimated to affect 55 million people worldwide, is defined as :

- a disruption in the fluency of verbal expression characterized by involuntary, audible or silent, repetitions or prolongations of sounds or syllables"

Source : PLoS Biol 2(2): e46

Over the centuries, a number of theories about how stuttering arises (and what treatment approaches should be used) have been proposed.

It tends to affect children more than adults - and boys four times more than girls. It's currently unknown whether stuttering is a cognitive, motor, or sensory disorder - or some combination of the three.

Recent progress in near-realtime brain imaging studies have found that :

(i) in stutterers, the right hemisphere seems to be hyperactive, and (ii) a timing problem seems to exist between the left frontal and the left central cortex."

[ source as above ]

Current medical treatments tend to be based around 'neuroleptic' (anti-psychotic) drugs such as haloperidol, risperidoneplugin-autotooltip__plain plugin-autotooltip_bigRisperidone

Risperidone, was widely approved for use in the late 1990s. Sold under the brand names Aleptan, Arketin, Diaforin, Krisp, Risperdal, Okedi and many others, it's used to treat Schizophrenia, Major Depressive Disorder, Stuttering, Tourette syndrome and sometimes Autism

"Exact mechanism of antipsychotic action has not been fully elucidated;, and olanzapine - which are also used to help control Tourette syndromeplugin-autotooltip__plain plugin-autotooltip_bigTourette syndrome

Tourette syndrome (TS or Tourette's) is a common neuro-psychiatric disorder which usually starts in childhood and is characterized by multiple motor tics and at least one vocal tic. These tics characteristically wax and wane in intensity and frequency, can be suppressed temporarily, and are typically preceded by an unwanted urge or sensation in the affected muscles. Some common tics are eye blinking, coughing, throat clearing, sniffing, swearing, and facial movements.

Notes:

[1] Several studies have documented the fact that over 90% of people who stutter in normal speech can sing song-lyrics without any difficulties. There is no explanation for this effect. [ Ref : Psychomusicology: Music, Mind and Brain Vol. 31, Iss. 1, 18-34 ]

[2] It's known that in some cases the disorder has a genetic component, as it tends to run in families. The associated genes have not been identified.