Imaging interconnections: MRI-DTI in aphasia

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  • Published: Mar 1, 2016
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Imaging interconnections: MRI-DTI in aphasia

Hub map

Diffusion Tensor Imaging (MRI-DTI) has been used to map the after effects on the brain's interconnections following stroke, in those patients suffering from speech problems, aphasia.

Diffusion Tensor Imaging (MRI-DTI) has been used to map the after effects on the brain's interconnections following stroke, in those patients suffering from speech problems, aphasia.

It is one of the classic symptoms of cerebral stroke, damage to the brain regions that control speech and reading comprehension destroyed by a blockage of blood flow, leave patients unable to speak or understand spoken or written language. These difficulties with language, known as aphasia are among the most debilitating effects. However, a new study published in the journal Restorative Neurology and Neuroscience based on MRI-DTI suggests that damage to the underlying connections among different areas of the brain may well be to blame for the severity of aphasia in particular patients.

The architecture of the brain, and more specifically the connections between regions is sometimes referred to as the "connectome". The connectome is made up of nodes representing different regions and their edges, the connections between the nodes. As with any network, some of the nodes are hubs, critical and fundamental to the overall organization and distribution of information throughout the system. Colloquially, researchers think of those network hubs as having an abundance of interconnections as being the "rich club network". Moreover, there is a growing body of evidence that suggests that damage to this rich club network can cause aphasia on a par with direct damage to the brain regions usually associated with speech and comprehension.

Aphasia assessment

The team investigated 44 patients who had experienced a left hemisphere ischaemic stroke at least six months prior to the study. Aphasia testing was carried out using the Western Aphasia Battery, which determines the degree of aphasia being experience by the patients. The patients were also assessed for speech fluency, auditory comprehension, speech repetition and naming. Ultimately, each participant was given an Aphasia Quotient (WAB-AQ) as a measure of severity. MRI-DTI was then used to map the interconnections between brain regions and to identify the rich club network in each individual patient and to see how WAB-AQ correlated with that map.

The team found that the post-stroke patients had different distributions of rich club nodes and this could lead to very different WAB-AQ for the patients. For instance, two patients with similar volumes of stroke damage had very different numbers of rich club nodes remaining nearby, one of those patients had a WAB-AQ of 23.6, the other 64.6. A score of 0 to 25 is considered very severe, 26-50 severe, 51-75 moderate and 76 and above is a mild degree of aphasia.

Spared regions

"Subjects whose spared cortical language regions are integrated into the remaining network as rich club nodes are less likely to have more severe forms of aphasia," explain lead investigators Ezequiel Gleichgerrcht and Leonardo Bonilha of the Department of Neurology, at the Medical University of South Carolina, USA.

Clinical care for stroke sufferers usually focuses on the brain's grey matter, but novel technology and techniques such as MRI-DTI are now opening up avenues of study and diagnostics in the increasingly important white matter connections present throughout the brain. "These findings further highlight the potential relevance and utility of mapping the neural connectome of individual subjects," the team says. "Identifying patterns of white matter integrity has the potential to add valuable information to the well-established volume-based analysis of clinical, neuropsychological, and language outcomes from both theoretical and clinical perspectives."

"Next steps for this research will be to evaluate whether preservation of hubs leads to better treatment related recovery from aphasia," Bonilha told SpectroscopyNOW.

Related Links

Restorative Neurol Neurosci, 2015, 34, 19-28: "Preservation of structural brain network hubs is associated with less severe post-stroke aphasia"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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