New Research Investigates Genetic Factors Responsible For Speech In Humans

Chuck Bednar for redOrbit.com – Your Universe Online
Two separate, recently published studies are shedding new light on how humans developed the ability to produce and understand speech, and what factors contribute to the development of language during infancy.
In the first study, researchers from MIT and several European universities report that the human version of a gene known as Foxp2 makes it easier to transform new experiences into routine procedures, and that engineering mice to express humanized Foxp2 allowed the rodents to run through a maze far more quickly than normal.
Their research indicates the gene could help people with one of the key components of learning languages – transforming the experience of hearing the word “glass” when viewing a glass of water – into an almost automatic association of that term with other objects that resemble and function like glasses, the researchers said.
“This really is an important brick in the wall saying that the form of the gene that allowed us to speak may have something to do with a special kind of learning, which takes us from having to make conscious associations in order to act to a nearly automatic-pilot way of acting based on the cues around us,” MIT professor Ann Graybiel said in a statement Monday.
Graybiel is a member of MIT’s McGovern Institute for Brain Research and one of the senior authors of a paper published in this week’s edition of the Proceedings of the Natural Academy of Sciences. The other senior author is Wolfgang Enard, a professor of anthropology and human genetics at Ludwig-Maximilians University. Christiane Schreiweis, a former visiting graduate student at MIT, and Ulrich Bornschein of the Max Planck Institute for Evolutionary Anthropology in Germany are the lead authors of the study.
While all animal species are capable of communicating with one another, humans are the only ones with the ability to generate and comprehend language, the researchers said. Foxp2 is one of several genes believed to have played a role in the development of these linguistic talents, and the study authors said that it was originally identified in a group of family members suffering from severe difficulties in both speaking and understanding speech.
Those individuals were found to have been carrying a mutated version of the Foxp2 gene, and in 2009, researchers from the Max Planck Institute engineered mice to express the human form of the Foxp2 gene, which encodes a protein that is different from the mouse version by just two amino acids.
Those scientists discovered that the mice had longer dendrites (which are thin extensions used by neurons to communicate with one another) in the striatum (which is a part of the brain associated with habit formation). Those rodents were also said to be better at forming new synapses or connections between neurons.
In the new study, Graybiel and her colleagues looked at the behavioral effects of replacing Foxp2. They reported that those mice with a humanized form of the gene were better at learning how to complete a maze in which the creatures had to decide whether to turn left or right at a T-shaped junction to earn a food reward.
This type of learning requires the use of both declarative memory (memory for events and places) and procedural memory (memory required for routine tasks), and based on their performance in both T-shaped and cross maze trials, the researchers believe that the humanized version of the Foxp2 gene made it easier for the rodents to convert declarative memories into habitual routines.
“In this study, the researchers found that Foxp2 appears to turn on genes involved in the regulation of synaptic connections between neurons. They also found enhanced dopamine activity in a part of the striatum that is involved in forming procedures,” Anne Trafton of the MIT News Office explained. “Together, these changes help to “tune” the brain differently to adapt it to speech and language acquisition, the researchers believe.”
In related research, scientists from the Medical Research Council (MRC) Integrative Epidemiology Unit at the University of Bristol and an international team of colleagues reported in Tuesday’s edition of Nature Communications that they had found a link between variations near the ROBO2 gene and the number of words spoken by kids who are learning how to talk.
According to the authors of this study, children begin producing words between the ages of 10 and 15 months, and their vocabulary range expands as they grow, going from approximately 50 words at the 15 to 18 months to 200 words at 18 to 30 months to over 14,000 words by the age of six and 50,000 before entering high school.
The researchers discovered the genetic link during the 15 to 18 month range, when toddlers are typically using single words to communicate and before their linguistic skills mature to two-word combinations and more complex grammar. The genetic region is on chromosome 3, which had previously been implicated in dyslexia and speech-related disorders, and involves a protein that directs chemicals in brain cells that could help infants develop language.
“This research helps us to better understand the genetic factors which may be involved in the early language development in healthy children, particularly at a time when children speak with single words only, and strengthens the link between ROBO proteins and a variety of linguistic skills in humans,” said co-lead investigator Dr. Beate St Pourcain of the University of Bristol’s Medical Research Council Integrative Epidemiology Unit.
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