UCLA scientists report parallels between human speech and the song of a bird, findings that may contain clues to human speech disorders.
The research by a team led by Stephanie White, UCLA assistant professor of physiological science, supports the theory that two genes shared by humans and songbirds, FoxP1 and FoxP2, may play a critical role in human speech, and speech disorders. The study is published March 31 in the Journal of Neuroscience.
"We examined the expression of FoxP1 and FoxP2 in embryonic human brains and found a striking correspondence between bird and human expression," said White, a member of UCLA's Brain Research Institute. "The similar expression patterns suggest that songbirds can be studied to investigate neural mechanisms for vocal learning that may be parallel to those used by the human brain.
"Our findings make it more likely that FoxP2 plays a critical role for learning speech and vocalization in both humans and the songbird," she said. "Understanding how FoxP1 and FoxP2 function in the songbird may reveal significant insights into human vocal learning and speech disorders."
FoxP2 is in the brain of the zebra finch in regions that control the learning of song, said White, who said that additional unknown molecules are likely to interact with the gene. The UCLA study is the first to address whether FoxP2 is critical for learned vocalizations in other species.
Male zebra finches learn to sing a courtship song that their female counterparts do not learn.
White's team detected increased level of the closely related gene, FoxP1, in "Area X" of the male zebra finch's brain, a critical part of the bird's song circuitry, and in two other song regions of the brain.
"The finding that FoxP2 is expressed in the song circuit is exciting," White said. "We are getting a green light for studying the songbird to try to understand these genes."
FoxP2 may interact with FoxP1, and both genes may be critical for human speech, said White, whose team used molecular genetic techniques. Increased understanding of these genes could potentially lead to new medications for speech disorders, she said.
As a master gene regulates eye development, "FoxP2 may be a master gene involved in setting up structures required for facial control and vocalization," White said.
White's team has shown that FoxP1 and FoxP2, while expressed early in life, stay on throughout the life of the songbird. "This implies that these genes may be involved in the lifelong process of speech," she said, adding that this idea is supported by evidence from a second team of researchers publishing separate findings in the same issue of the Journal of Neuroscience, based on studies of adult canaries, which sing seasonally." (The second team includes scientists from Germany's Max Planck Institute for Molecular Genetics, Duke University, City University of New York, and the University of Pennsylvania. They showed that FoxP2's expression in Area X in canaries changes with the seasons, which is more evidence that FoxP2 is involved in vocal learning.)
A study published in 2001 revealed a single mutation in FoxP2 in each member of a family in England with a severe speech disorder; many members of this family, over three generations, have the speech disorder, and each of these family members has the mutation, while those family members without the speech disorder do not have this mutation.
If the human and songbird mechanisms underlying vocal learning are parallel, White would expect FoxP1 and FoxP2 would overlap in the same regions of the human brain. "That turned out to be true; these genes are in analogous regions of the human brain and the zebra finch brain," she said.
White's co-authors are Ikuko Teramitsu, a UCLA graduate student in molecular, cellular, and integrative physiology, who conducts research in White's laboratory; Daniel H. Geschwind, an associate professor of neurology in UCLA's David Geffen School of Medicine, who works with people with language disorders; Lili Kudo, a UCLA graduate student of neuroscience in Geschwind's laboratory; and Sarah E. London, a UCLA graduate student of neuroscience.