Millions of people suffer from stuttering, but little is known about the causes of this language disorder. Researchers have now developed a model in which they use a drug to make zebra finches stutter. The intervention causes certain neurons in the bird’s brain to fire excessively. As a result, the finches change their song patterns and show symptoms that are similar to human stuttering. The study reveals insights into neural plasticity and gives hope to develop treatment approaches for human stutterers.
Zebra finches learn their singing motifs as young animals by singing afterwards, similar to how small children learn to speak. Once the birds have learned the appropriate tone sequences, they usually remain unchanged in adulthood. A brain region in the area of the cortical basal ganglia plays an important role in the learning of melodies in birds. If this region is damaged, the song repertoire of the animals remains limited. Previous studies have already shown that birds in which this brain region is stimulated change their melodies and incorporate motifs that resemble human stuttering. The previous studies, however, only focused on short-term interventions.
Stuttering singing triggered
A team led by Sanne Moorman from the University of Utrecht in the Netherlands has now tested the effects of artificially increasing the activation of this region in the bird’s brain over a longer period of time. To do this, they administered a drug over several days to adult zebra finches that made certain neurons that are important for song fire stronger. “On the first day of the intervention, the birds mostly continued to sing their stereotypical motifs, but sometimes broke them off prematurely, dropped syllables or produced abnormal syllables,” the researchers report. “After several days, new features appeared in the vocal spectrum and the proportion of abnormal chants increased.”
Among other things, the birds repeated some syllables several times and took excessively long pauses before moving on to the next section of their song – much like what can be observed with stuttering people. These changes persisted even after the researchers stopped taking the drug. Apparently the increased firing of the singing neurons had led to the new patterns being taken over into motor memory. “This work suggests that firing these neurons is important in making long-lasting changes in the vocal sequences,” says co-author Mimi Kao of Tufts University in Massachusetts. “The mechanism could potentially also be used specifically to restore normal vocal sequences.”
Reversible disorder
After drug treatment was discontinued, it took days to weeks for the birds to return to their original song patterns. Previous studies had achieved a similar effect by confusing the birds with other noises. If the animals lacked auditory feedback because they could no longer hear their own singing sufficiently, this led to mismatches similar to those of drug intervention. From the researchers’ point of view, it could be that the drug also had an influence on the auditory feedback. It is possible that the sensory information about its own song was no longer processed correctly in the bird’s brain.
After the acoustic as well as the drug disturbance, normal singing returned after a while. That gives hope for future treatments for stutterers. If persistent deviant fire patterns in the brain can cause speech disorders, correcting those fire patterns could enable normal speech. “Although the brain regions examined in this study are known to be involved in speech disorders, very little is known about the specific neural fire patterns that play a role,” says Moorman. “This research provides a way to manipulate the fire patterns so that we can learn how they contribute to dysfunctional language. We can also research pharmaceutical or other treatments to restore normal function. ”This could also benefit people whose speech disorders are due to neurological diseases such as Parkinson’s.