fMRI identifies language-specific areas of brain
According to Evelina Fedorenko, a research scientist in MIT’s Department of Brain and Cognitive Sciences and lead author of the study, the research addresses one of the biggest questions in neuroscience: What are the key components of the human brain?
“One way in which we know to ask this kind of question is by looking at functional specialization,” said Fedorenko in an interview with Health Imaging News. “So seeing whether a particular brain region, for example, is specialized for one type of mental computation or whether, instead, it’s doing a whole bunch of things.”
Functional specificity had previously been discovered in other domains. Some regions are dedicated to motor functions, while others respond to faces, for example. Linguistic ability, though, had never been definitively shown to have a dedicated region of the brain.
Prior to the MIT study, research using functional MRI (fMRI) was inconclusive. Areas of the brain activated by language also seemed to be activated by music and arithmetic or used for general memory.
Still, language seemed to be a prime candidate for functional specificity. Specific linguistic capabilities can be affected by brain trauma or stroke, and language skills are universal to all human cultures, leading researchers like Fedorenko to continue to push the issue.
The primary difference in the MIT study compared to previous research was in methodology. Other studies may have asked the question, but they were asking it the wrong way, according to Fedorenko.
fMRI studies of language had generally been conducted as a group analysis, with the results averaged together to map the various brain regions. Dozens of subjects would be analyzed and activations in the brain would show up in the common brain space.
The problem with this method is that separate regions tend to blend together in the average data and appear to be activated by multiple tasks. In reality, it is two nearby regions responding to different stimuli, but researchers might assume it’s the same region, explained Fedorenko.
“Especially in the frontal lobe this is a problematic inference to make because frontal lobes consist of a whole bunch of distinct patches with different cellular properties,” said Fedorenko. “So finding some activation in one study and then relating it to activation in another study is just not ideal because you may be actually talking about nearby but distinct regions.”
Fedorenko and colleagues instead analyzed each subject individually, comparing activation patterns from task-to-task in the same brain only.
The study’s 48 participants, all English-speakers between the ages of 18 and 40, were first given language localizer tasks such as reading sentences and pronounceable nonwords. They were then given nonlinguistic tasks, including solving math problems and listening to music, commonly thought to engage the same regions as linguistic processes.
While nearby regions of the brain were activated by the different tasks, very little evidence of overlap was detected, suggesting there are regions of the brain specialized for linguistic processing.
Fedorenko acknowledged that proving functional specificity is challenging, and it’s possible a future study might discover overlap between language and some other process that hasn’t been tested.
“At least if we take a bunch of claims from the literature about language sharing mental processes with some non-language function like music or general memory and we test these claims and we show these regions don’t actually support these non-language functions, then we’re quite a bit further ahead of where we were,” said Fedorenko.
This research could eventually lead to therapies for people who have lost language functions, though more testing is needed to confirm functional specificity and, if it is confirmed, map out which language-specific regions handle various linguistic tasks, said Fedorenko.