Neuroimaging: New Research and Online Resources Neuroscientists at the Massachusetts Institute of Technology have identified a new method to analyze brain imaging data that may clarify how the brain produces and understands language. Previous research with patients who developed specific language deficits (such as the inability to comprehend passive sentences) following brain injury suggested that ... Research in Brief
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Research in Brief  |   July 01, 2010
Neuroimaging: New Research and Online Resources
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Special Populations / Older Adults & Aging / Telepractice & Computer-Based Approaches / Research in Brief
Research in Brief   |   July 01, 2010
Neuroimaging: New Research and Online Resources
The ASHA Leader, July 2010, Vol. 15, 20-21. doi:10.1044/leader.RIB.15082010.20
The ASHA Leader, July 2010, Vol. 15, 20-21. doi:10.1044/leader.RIB.15082010.20
Analysis Reveals Brain’s Language Areas
Neuroscientists at the Massachusetts Institute of Technology have identified a new method to analyze brain imaging data that may clarify how the brain produces and understands language. Previous research with patients who developed specific language deficits (such as the inability to comprehend passive sentences) following brain injury suggested that different aspects of language reside in different parts of the brain, but attempts to find these functionally specific regions with current neuroimaging technologies have been inconsistent and controversial. One reason for this inconsistency may be the studies’ reliance on group analyses, in which brain imaging data were averaged across multiple subjects—a computation that could introduce statistical noise and bias into the analyses.
Because brains differ in their folding patterns and in how functional areas map onto these folds, activations obtained in functional MRI studies often do not precisely line up across brains. Some regions of the brain thought to be involved in language are close to regions that support other cognitive processes like music, arithmetic, or working memory. Spatially averaging brain data across subjects may result in an activation “blob” that appears to support both language and arithmetic, for example, even when these two processes are supported by non-overlapping nearby bits of cortex in every subject.
To avoid this problem, the researchers first defined “regions of interest” in each individual subject and then investigated those regions by examining the subjects’ responses to various new tasks. They developed a “localizer” task in which subjects read either sentences or sequences of pronounceable nonwords. By subtracting the nonword-activated regions from the sentence-activated regions, the researchers found a number of language regions that were reliably identified in individual brains. Their new method revealed higher selectivity for sentences compared to nonwords than a traditional group analysis applied to the same data. This new, more sensitive method allows investigation of functional specificity between language and other cognitive functions, as well as between different aspects of language. The research appears in the Journal of Neurophysiology (April 21, 2010).
Neuroimaging May Help Identify Alzheimer’s Treatments
A new neuroimaging instrument is effective in detecting deposits of amyloid-beta protein plaques in the brain—a condition central to the development of Alzehimer’s disease (AD) previously detectable only on autopsy. The tool, PIB-PET, was tested in more than 100 studies. The study also shows that older individuals with amyloid deposits were much more likely to show cognitive decline over time than their “amyloid-negative” counterparts. The deposits appear to reach a plateau early in the course of the disease, however, when patients experience mild or no symptoms. This finding may explain why patients with AD have not responded to experimental drugs that target amyloid—by the time patients have developed AD symptoms, clinical decline and brain changes are occurring independently of further amyloid accumulation. It also suggests that amyloid-based treatments are most likely to work earlier in the disease process.
PIB-PET involves injecting a tracer material (PIB) into the brain via the bloodstream and imaging the brain with positron emission tomography (PET). PIB binds to amyloid-beta protein plaques and sends a signal that is then detected by the PET scanner and translated into an image reflecting the quantity and distribution of amyloid in the brain. In the studies surveyed, scientists complemented the PIB-PET investigations by using additional neuroimaging techniques such as magnetic resonance, which allowed them to measure the size of different brain structures, network connections, or brain metabolism.
Researchers predict that the technology might be used for screening those genetically at risk for Alzheimer’s, as well as those who are minimally symptomatic. Anti-amyloid treatments would then be prescribed to prevent the onset of the disease.
The results of the study are reported in Behavioural Neurology (Vol. 21, Issues 1–2).
Localization of Sublexical Speech Perception Components
Researchers at the University of Pennsylvania conducted meta-analyses of the neuroimaging literature on sublexical speech perception to refine models of speech perception, which generally agree on which major cortical regions are involved, but lack precision about the localization and lateralization of processing units.
Significant activation likelihoods in the left and right superior temporal cortex and the left posterior middle frontal gyrus were identified in 23 functional MRI experiments. Sub-analyses that examined phonetic and phonological processes revealed only left mid-posterior superior temporal sulcus activation likelihood. Analysis demonstrated that experiments requiring explicit attention to phonology were associated with temporal lobe left lateralization (increased magnitude, extent, and consistence of activity).
An analysis of eight fMRI studies on categorical phoneme perception revealed significant activation likelihood in the left supramarginal gyrus and angular gyrus. These results are consistent with a speech processing network in which the bilateral superior temporal cortices perform acoustic analysis of speech and non-speech auditory stimuli, the left mid-posterior superior temporal sulcus performs phonetic and phonological analysis, and the left inferior parietal lobule detects differences between phoneme categories.
The results modify current speech perception models in three ways: specifying the most likely locations of dorsal stream processing units; clarifying that phonetic and phonological superior temporal sulcus processing is left lateralized and localized to the mid-posterior portion; and suggesting that both the supramarginal gyrus and angular gyrus may be involved in phoneme discrimination. The study appears in the July issue of Brain and Language.
Resources at www.asha.org
The ASHA Leader
American Journal of Speech-Language Pathology
Journal of Speech, Language, and Hearing Research
Special Interest Division 2
Special Interest Division 2, Neurophysiology and Neurogenic Speech and Language Disorders and its Perspectives publication
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July 2010
Volume 15, Issue 8