Many neurological disorders can rob someone of the ability to speak clearly, causing them to stutter, mispronounce words, and struggle to put together coherent sentences. However, the molecular and neurological dysfunctions that cause these symptoms aren't well understood. New research may give scientists a new tool to better study these vocal and speech impairments, particularly in Huntington's disease. The research is described in a paper published in Nature Neuroscience.
Like humans, songbirds and a few other types of birds can learn vocalizations. Researchers used one such songbird, zebra finches, which are small, red-beaked birds common in pet stores, for the foundation of his research on neurodegeneration.
The experiments began by breeding finches with a singular genetic mutation - the introduction of mHTT, the mutant human gene responsible for Huntington's disease. An inherited disorder that results in the progressive breakdown of nerve cells in the brain, Huntington's leads people to lose control of their speech and movement, as well as to cognitive decline. Because Huntington's is determined by a single gene, the researchers were able to easily isolate its effects on the birds.
The team introduced the mHTT gene into eggs, then screened the chicks for the mutation once they hatched. The birds that had it were then used to breed successive generations, in whom the genetic mutation occurred naturally. That way the researchers could ensure that each bird developed the disease as it would manifest in humans.
As they grew, the transgenic finches all began to display the behavior disorders associated with Huntington's, such as tremors sometimes seen in patients. Most of the mutant males, the singing sex, had problems learning their songs while young and, once fully grown, produced aberrant songs.
Using specialized computer software, the researchers were able to monitor subtle changes in these finches' song as their muscular degradation progressed, providing detailed records of how vocal patterns were affected. This kind of progressive speech impairment is associated with dysfunction in the cortical-basal ganglia brain circuit in both humans and songbirds, so the researchers could make assumptions based on this trial about how the human brain circuit changes. Their result are the clearest findings to date as to how this kind of neurodegeneration occurs.
In recent years, songbirds' similarities to human vocal learning have piqued researchers' interests in using them as a functional animal model to study the neurological basis for Huntington's disease.
It is difficult to overstate the potential value of such a tool in attempts to better understand, prevent, and treat this disorder, the researchers said. For the first time, scientists will be able to test out therapeutic treatments on vocal degeneration.
Based on material originally posted by Rockefeller University.