UCLA scientists report parallels between human speech andthe song of a bird, findings that may contain clues to human speech disorders.
The research by a team led by Stephanie White, UCLAassistant professor of physiological science, supports the theory that twogenes shared by humans and songbirds, FoxP1 and FoxP2, may play a critical rolein 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 embryonichuman brains and found a striking correspondence between bird and humanexpression," said White, a member of UCLA's Brain Research Institute. "The similar expression patterns suggestthat songbirds can be studied to investigate neural mechanisms for vocal learningthat may be parallel to those used by the human brain.
"Our findings make it more likely that FoxP2 plays acritical role for learning speech and vocalization in both humans and thesongbird," she said. "Understanding howFoxP1 and FoxP2 function in the songbird may reveal significant insights intohuman vocal learning and speech disorders."
FoxP2 is in the brain of the zebra finch in regions thatcontrol the learning of song, said White, who said that additional unknownmolecules are likely to interact with the gene. The UCLA study is the first to address whether FoxP2 is criticalfor learned vocalizations in other species.
Male zebra finches learn to sing a courtship song that theirfemale counterparts do not learn.
White's team detected increased level of the closely relatedgene, FoxP1, in "Area X" of the male zebra finch's brain, a critical part ofthe bird's song circuitry, and in two other song regions of the brain.
"The finding that FoxP2is expressed in the song circuit is exciting," White said. "We are getting a green light for studyingthe songbird to try to understand these genes."
FoxP2 may interact withFoxP1, and both genes may be critical for human speech, said White, whoseteam used molecular genetic techniques.Increased understanding of thesegenes could potentially lead to new medications for speech disorders, she said.
As a master gene regulates eye development, "FoxP2 may be amaster gene involved in setting up structures required for facial control andvocalization," White said.
White's team has shown that FoxP1 and FoxP2, while expressedearly in life, stay on throughout the life of the songbird. "This implies that these genes may beinvolved in the lifelong process of speech," she said, adding that this idea issupported by evidence from a second team of researchers publishing separatefindings in the same issue of the Journal of Neuroscience, based on studies ofadult canaries, which sing seasonally."(The second team includes scientists from Germany's Max Planck Institutefor Molecular Genetics, Duke University, City University of New York, and theUniversity of Pennsylvania. They showedthat FoxP2's expression in Area X in canaries changes with the seasons, whichis more evidence that FoxP2 is involved in vocal learning.)
A study published in 2001 revealed a single mutation inFoxP2 in each member of a family inEngland with a severe speech disorder; many members of this family, over threegenerations, have the speech disorder, and each of these family members has themutation, while those family members without the speech disorder do not havethis mutation.
If the human and songbird mechanisms underlying vocallearning are parallel, White would expect FoxP1 and FoxP2 would overlap in thesame regions of the human brain. "Thatturned out to be true; these genes are in analogous regions of the human brainand 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 ofneurology in UCLA's David Geffen School of Medicine, who works with people withlanguage disorders; Lili Kudo, a UCLAgraduate student of neuroscience in Geschwind's laboratory; and Sarah E.London, a UCLA graduate student of neuroscience.
Male zebra finchesare sexually mature 100 days after birth, and have learned their courtship songby then, starting about 35 days after birth.
"There are criticalperiods in song learning," noted White, who joined UCLA's faculty in 2000 afterearned her Ph.D. at Stanford in neuroscience, and then conducted postdoctoralresearch at Duke University. "If we can learn what FoxP1 and FoxP2are doing during these periods, then we may be able to highlight keydevelopmental moments in children, to make sure the genes function properly atcritical periods."
While White's team has not established the role FoxP2 playsin the male zebra finch's learning of the courtship song, they have found that itis in the right part of the brain (the striatum) to play a critical role in thelearning of vocalization.
White and her team will continue research on FoxP1 andFoxP2, and the interaction between them, in the zebra finch and otherbirds. She is interested in learningwhich genes are regulated by FoxP2, and which gene is required for vocallearning?
White's research is funded by the National Alliance forAutism Research, the Alfred P. Sloan Foundation, a MIND scholarship, and theMental Retardation Research Center at UCLA.
White is interested in understanding social influences on learning, and on the neural changesthat underlie learning.
"Songbirds areperfect for these questions because they learn their courtship and territorialsongs through social interactions with other songbirds," she said. "We want to understand the neural mechanismsthat underlie vocal learning and see how social and environmental influencesalter the learning, where that is happening in the brain, and what moleculesare changing. I'm very interested inhuman behavior, but humans are too complicated to study rigorously atthe cellular and synaptic level.
"Language isuniquely human, but it has components, such as the ability to create newsounds; the zebra finch does that. Itcreates new sounds like instrumental music, and may do that using the samegenes as humans."
There areapproximately 9,000 species of birds, approximately 4,000 of which aresongbirds. There are more similaritiesbetween the human brain and the songbird's brain than many people may realize,White said. The term"bird-brain" may not be such a put-down after all.