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Mapping Behavior to Lesion Location in Neurolinguistics: History and The Illusive Methodology
Poster Session E, Sunday, September 14, 11:00 am - 12:30 pm, Field House
This poster is part of the Sandbox Series.
Danielle Fahey3, Shea Highfill1, Jeremy Yeaton2; 1University of Montana, 2University of California, Irvine, 3University of Alabama
Lesion-to-symptom mapping (LSM) correlates brain damage location in patients with cognitive function, providing crucial evidence for understanding the neurobiology of language. Today, voxel-based lesion-symptom mapping (VLSM) using manual lesion segmentation is widely used, with automatic segmentation gaining popularity. However, there is a lack of training resources for the segmentation process. Herein, we survey the history of LSM techniques, highlighting the need for broader documentation and training materials in our field. The development of aphasiology began with research analyzing brain lesions to identify language-related cortical regions. Early researchers like Paul Broca, Carl Wernicke, and Ludwig Lichtheim used case data and autopsy correlations to link brain damage with language functions. However, their work omitted systematic methodological descriptions, limiting reproducibility. Jules Dejerine and Joseph Jules Montier made more detailed lesion observations, but much of their work remains poorly documented by modern standards. Overall, early aphasia research focused on clinical symptoms rather than precise anatomical localization, a trend that continued into early neuroimaging. Brain imaging started with the advent of X-rays in 1896, allowing researchers to examine damage in living patients. X-rays pass through tissues, with dense structures like bone appearing white and softer tissues darker. However, X-ray images are grainy, 2D, and limited in localization, with higher radiation risks. Nearly a century later, imaging technologies like PET, CT, MEG, and MRI revolutionized clinical neurology. PET scans, developed from radioactive imaging techniques and first used by scientists at CERN, detect radiation from a tracer injected into the body to highlight metabolic activity. CT scans, invented by music industry engineer Godfrey Hounsfield, use a rotating X-ray beam to capture cross-sectional images, which can be combined into 3D images. MEG detects brain activity via tiny magnetic fields using sensitive Superconducting Quantum Interference Devices (SQUIDs). MRI uses a magnetic field to align hydrogen protons in the body, then uses radio waves to temporarily knock them out of alignment. As the protons relax, they emit signals that are detected and processed into detailed images. Functional MRI (fMRI), introduced in the 1990s, measures blood-oxygen-level-dependent (BOLD) signals to map brain activity with improved spatial resolution. VLSM involves outlining brain lesions on patients’ MRI scans, then correlating lesion locations with cognitive deficits. Each techniques offer superior soft tissue contrast compared to earlier methods, but with distinct advantages and limitations. PET scans provide insights into metabolic activity but involve radiation and have lower spatial resolution. CT scans are fast and effective for bone imaging but expose patients to radiation and offer poor soft tissue contrast. MEG provides excellent temporal resolution but is expensive and has limited spatial resolution. MRI delivers high spatial resolution and excellent soft tissue contrast without radiation but is slow, sensitive to movement, and unsuitable for individuals with metal implants. With advancements in neuroimaging, lesion-based study methods have become more complex. However, modern lesion mapping techniques still have limited documentation and training protocols, highlighting the need for dedicated literature on best practices. By reflecting on the historical challenges in technological improvements, we can improve current methodological practices and accessibility.
Topic Areas: History of the Neurobiology of Language, Methods