The closest thing to a stuttering mouse has been created by scientists who gave rodents a genetic mutation that causes the speech disorder in humans.
Mouse pups recorded in the first week of life squeaked with more pauses and displayed more repetitive, halting patterns in the noises they produced when they carried the mutation.
But the mutated mice had no other obvious language problems and squeaked out the same rich repertoire of ultrasonic syllables – defined by abrupt changes in pitch – as normal mice.
Researchers at Washington University in St Louis worked on the mice to see whether some of the characteristics of human stuttering, or stammering, can be reproduced in rodents. The research aims to help scientists unpick the biological pathways that underpin stammering, and give them a ready way to test drugs and other potential treatments.
These mice aren’t stuttering but they show a lot of features that are similar to a human that stutters, so this is an incredibly powerful research tool,” said Terra Barnes, whose study is published in Current Biology. “This is a huge first step towards an animal model of stuttering.”
“Once you have an animal model for the condition, you can do a lot of things you can’t do with humans. We can find the neural correlates of stuttering, identify the underlying biological mechanisms, and maybe work out how to fix it,” she added.
In the past, stammering has been blamed on anxiety, stress and even bad parenting, but the primary driver for the disorder is now considered biological, with stress potentially exacerbating the condition. In 2008, scientists at Oxford University identified changes in the brain that appear to disrupt the neural pathways needed for fluent speech.
Two years later, a team led by Dennis Drayna at the National Institute on Deafness and other Communication Disorders in Maryland, found mutations in a gene called Gnptab that appeared to cause stuttering in some people. The discovery was a surprise, because the gene is only considered important for general housekeeping duties, such as digesting waste inside the bodies’ cells.
To find out whether rodents can be made to stutter, or at least display some aspects of the condition, Barnes, Drayna and other colleagues created mice that carried the Gnptab mutations. They then recorded the noises the mice made until they were eight days old. Mouse pups make spontaneous sounds when they are taken from their mothers, but also when they are in pain, meet another mouse, or want to attract a mate.
Each recording session lasted 3.5 minutes. The mutated mice produced nearly a third fewer sounds, with longer pauses between the noises they made. Within bouts of vocal activity, the mutated mice squeaked out more single syllables than their natural littermates. The pauses are similar to the hesitations that can break up the smooth flow of speech in people who stutter, while the repetition of syllables also mirrors human stammering.
While speech remains a uniquely human skill, the patterns of speech are built on simple building blocks. To speak clearly, people have to control the timing of their breath, the fine muscles in the tongue and mouth, and be able to initiate the movements. “Those kinds of things may be shared all the way from mice to people,” said Tim Holy, a senior author on the study.
The modified mice could help researchers work out how mutations in the Gnptab gene give rise to stammering and shed light on the related mystery of how the mutation, which would affect every cell in the body, leads to a condition as specific as stuttering...
“Twin studies have long supported the view that there is a genetic element in stuttering. It also tends to run in some families: Charles Darwin stuttered, as did his Grandfather, Erasmus,” said Robin Lickley, a reader in speech and hearing sciences at Queen Margaret University in Edinburgh. “The genetic mutations probably affect the neurological processes that support speech production. So they probably conspire to create a neurological condition.”
Watkins KE, Smith SM, Davis S, Howell P. Structural and functional abnormalities of the motor system in developmental stuttering. Brain. 2008 Jan;131(Pt 1):50-9.ReplyDelete
Though stuttering is manifest in its motor characteristics, the cause of stuttering may not relate purely to impairments in the motor system as stuttering frequency is increased by linguistic factors, such as syntactic complexity and length of utterance, and decreased by changes in perception, such as masking or altering auditory feedback. Using functional and diffusion imaging, we examined brain structure and function in the motor and language areas in a group of young people who stutter. During speech production, irrespective of fluency or auditory feedback, the people who stuttered showed overactivity relative to controls in the anterior insula, cerebellum and midbrain bilaterally and underactivity in the ventral premotor, Rolandic opercular and sensorimotor cortex bilaterally and Heschl's gyrus on the left. These results are consistent with a recent meta-analysis of functional imaging studies in developmental stuttering. Two additional findings emerged from our study. First, we found overactivity in the midbrain, which was at the level of the substantia nigra and extended to the pedunculopontine nucleus, red nucleus and subthalamic nucleus. This overactivity is consistent with suggestions in previous studies of abnormal function of the basal ganglia or excessive dopamine in people who stutter. Second, we found underactivity of the cortical motor and premotor areas associated with articulation and speech production. Analysis of the diffusion data revealed that the integrity of the white matter underlying the underactive areas in ventral premotor cortex was reduced in people who stutter. The white matter tracts in this area via connections with posterior superior temporal and inferior parietal cortex provide a substrate for the integration of articulatory planning and sensory feedback, and via connections with primary motor cortex, a substrate for execution of articulatory movements. Our data support the conclusion that stuttering is a disorder related primarily to disruption in the cortical and subcortical neural systems supporting the selection, initiation and execution of motor sequences necessary for fluent speech production.
Kang C, Riazuddin S, Mundorff J, Krasnewich D, Friedman P, Mullikin JC, Drayna D. Mutations in the lysosomal enzyme-targeting pathway and persistent stuttering. N Engl J Med. 2010 Feb 25;362(8):677-85.ReplyDelete
Stuttering is a disorder of unknown cause characterized by repetitions, prolongations, and interruptions in the flow of speech. Genetic factors have been implicated in this disorder, and previous studies of stuttering have identified linkage to markers on chromosome 12.
We analyzed the chromosome 12q23.3 genomic region in consanguineous Pakistani families, some members of which had nonsyndromic stuttering and in unrelated case and control subjects from Pakistan and North America.
We identified a missense mutation in the N-acetylglucosamine-1-phosphate transferase gene (GNPTAB), which encodes the alpha and beta catalytic subunits of GlcNAc-phosphotransferase (GNPT [EC 188.8.131.52]), that was associated with stuttering in a large, consanguineous Pakistani family. This mutation occurred in the affected members of approximately 10% of Pakistani families studied, but it occurred only once in 192 chromosomes from unaffected, unrelated Pakistani control subjects and was not observed in 552 chromosomes from unaffected, unrelated North American control subjects. This and three other mutations in GNPTAB occurred in unrelated subjects with stuttering but not in control subjects. We also identified three mutations in the GNPTG gene, which encodes the gamma subunit of GNPT, in affected subjects of Asian and European descent but not in control subjects. Furthermore, we identified three mutations in the NAGPA gene, which encodes the so-called uncovering enzyme, in other affected subjects but not in control subjects. These genes encode enzymes that generate the mannose-6-phosphate signal, which directs a diverse group of hydrolases to the lysosome. Deficits in this system are associated with the mucolipidoses, rare lysosomal storage disorders that are most commonly associated with bone, connective tissue, and neurologic symptoms.
Susceptibility to nonsyndromic stuttering is associated with variations in genes governing lysosomal metabolism.
Ward D, Connally EL, Pliatsikas C, Bretherton-Furness J, Watkins KE. The neurological underpinnings of cluttering: Some initial findings. J Fluency Disord. 2015 Mar;43:1-16.ReplyDelete
Cluttering is a fluency disorder characterised by overly rapid or jerky speech patterns that compromise intelligibility. The neural correlates of cluttering are unknown but theoretical accounts implicate the basal ganglia and medial prefrontal cortex. Dysfunction in these brain areas would be consistent with difficulties in selection and control of speech motor programs that are characteristic of speech disfluencies in cluttering. There is a surprising lack of investigation into this disorder using modern imaging techniques. Here, we used functional MRI to investigate the neural correlates of cluttering.
We scanned 17 adults who clutter and 17 normally fluent control speakers matched for age and sex. Brain activity was recorded using sparse-sampling functional MRI while participants viewed scenes and either (i) produced overt speech describing the scene or (ii) read out loud a sentence provided that described the scene. Speech was recorded and analysed off line. Differences in brain activity for each condition compared to a silent resting baseline and between conditions were analysed for each group separately (cluster-forming threshold Z>3.1, extent p<0.05, corrected) and then these differences were further compared between the two groups (voxel threshold p<0.01, extent>30 voxels, uncorrected).
In both conditions, the patterns of activation in adults who clutter and control speakers were strikingly similar, particularly at the cortical level. Direct group comparisons revealed greater activity in adults who clutter compared to control speakers in the lateral premotor cortex bilaterally and, as predicted, on the medial surface (pre-supplementary motor area). Subcortically, adults who clutter showed greater activity than control speakers in the basal ganglia. Specifically, the caudate nucleus and putamen were overactive in adults who clutter for the comparison of picture description with sentence reading. In addition, adults who clutter had reduced activity relative to control speakers in the lateral anterior cerebellum bilaterally. Eleven of the 17 adults who clutter also stuttered. This comorbid diagnosis of stuttering was found to contribute to the abnormal overactivity seen in the group of adults who clutter in the right ventral premotor cortex and right anterior cingulate cortex. In the remaining areas of abnormal activity seen in adults who clutter compared to controls, the subgroup who clutter and stutter did not differ from the subgroup who clutter but do not stutter.
Our findings were in good agreement with theoretical predictions regarding the neural correlates of cluttering. We found evidence for abnormal function in the basal ganglia and their cortical output target, the medial prefrontal cortex. The findings are discussed in relation to models of cluttering that point to problems with motor control of speech.
This paper reports findings on the neural correlates seen in adults who clutter, and offers hypotheses as to how these might map onto the behaviours seen amongst those who clutter. Readers will be able to (a) identify the structures that are implicated in the disorder of cluttering, (b) understand arguments relating these structures to the behavioural expression of the disorder, (c) understand some of the complexities in interpreting data pertaining to recovery from cluttering, (d) understand where future efforts in research into the neurological correlates of cluttering should be focussed.
They might not huddle round a marvellous mechanical mouse organ or live with an old cloth cat called Bagpuss, but scientists have discovered that mice are more musical than their simple squeaks suggest.ReplyDelete
Research by a team of neuroscientists has revealed that male mice construct complex songs and sing them for minutes at a time when they come across sex pheromones produced by potential mates. The songs are not audible to the human ear because they are too high frequency and although scientists knew mice emitted ultrasonic chirps, recordings of the noises had never been fully analysed.
Tim Holy and Zhongsheng Guo at Washington University School of Medicine in Missouri discovered the murine melodies by accident. In experiments to test how male mice responded to sex pheromones - chemicals which are found in the urine of female mice - they recorded males as they sniffed cotton swabs dunked in urine from females, males and a mixture of the two.
"We were trying to find out the brain mechanisms they used to detect and recognise pheromones, but we noticed the sounds they made on encountering swabs were interesting in their own right," said Dr Holy, whose study appears in the open access journal, Public Library of Science, Biology.
Instead of turning up their snouts, within seconds of encountering the scent of female mouse urine, the males broke into ultrasonic song. Dr Holy and his team processed the sound recordings on a computer and made them audible to the human ear, first by slowing down the entire audio track, and then by keeping the tempo but significantly lowering the pitch. "The first moment I heard them I thought they sounded like songs, and they really do," said Dr Holy.
If the researchers are right, it will elevate mice to an exclusive musical club until now populated mostly by birds, whales, dolphins and gibbons.
The mice used in the experiment were genetically identical and the same age, but still the songs varied widely from mouse to mouse. Some showed a preference for certain syllables over others while others varied how long they spent on different syllables. There is no universal definition of song, but variations in the sounds made and a structure that gives the utterances rhythm make for more convincing songs, said Dr Holy. "Instead of making sounds randomly, mice tend to repeat certain syllables a number of times, then shift to a different syllable. It sounds a lot like the twittering of a bird," he said.
In many bird species, song helps in mate selection, with females choosing males with the most impressive melodies.
"We don't know for sure why mice sing, but it probably plays a part in courtship. But whether a male gains an advantage when it comes to mating by singing well is something nobody has yet looked at," said Dr Holy.
Because mice can easily be genetically modified to test the importance of different genes, the discovery could have a huge impact on research as diverse as the origins of speech, the causes of speech defects and the role of song.
Holy TE, Guo Z (2005) Ultrasonic Songs of Male Mice. PLoS Biol 3(12): e386. doi:10.1371/journal.pbio.0030386ReplyDelete
Previously it was shown that male mice, when they encounter female mice or their pheromones, emit ultrasonic vocalizations with frequencies ranging over 30–110 kHz. Here, we show that these vocalizations have the characteristics of song, consisting of several different syllable types, whose temporal sequencing includes the utterance of repeated phrases. Individual males produce songs with characteristic syllabic and temporal structure. This study provides a quantitative initial description of male mouse songs, and opens the possibility of studying song production and perception in an established genetic model organism.