Preliminary Characterization of Language Network Connectivity in a Logopenic Alzheimer’s Population Using Task-based fMRI
Lucas Oland1, Anne Trainer1, Bronte Ficek-Tani1, Joyce Li1, Samantha Tun1, Suyeon Ju1, Cheryl Lacadie2, Todd Constable3, Nadine Martin4, Carolyn Fredericks1
1Neurology, 2Radiology and Biomedical Engineering, 3Radiology, Biomedical Engineering, and Neurosurgery, Yale School of Medicine, 4Communication Sciences and Disorders, Temple University, College of Public Health
Objective:
To investigate task-based functional connectivity differences of a posterior temporal language network in logopenic variant primary progressive aphasia (lvPPA) during a working language memory task.
Background:
lvPPA is characterized by predominant deficits in language function with underlying Alzheimer’s pathology. Patients typically have the greatest atrophy at the left temporoparietal junction and corresponding decreases in resting connectivity within a posterior temporal language network seeded from this region. We hypothesized that early-stage lvPPA patients would show lower connectivity within the posterior temporal language network, but would recruit regions outside of the network, in performing the task.
Design/Methods:
6 patients with early-stage lvPPA (average CDR 0.5) and 9 matched controls underwent functional magnetic resonance imaging while performing the Phonological Short-Term Memory Probe task from the TALSA battery. Patients hear 3 words, a pause, then must determine if a 4th unique word rhymes with any of the original set by pushing a button. A 4-mm radius sphere at the temporoparietal junction, derived from the peak atrophy point in a previously published lvPPA population, was used as the seed for preliminary seed-to-voxel functional connectivity analysis (height by extent threshold of p <0.05, p <0.05).
Results:
Task performance was worse in the lvPPA cohort (lvPPA accuracy averaged 58%; HC averaged 92%). In functional connectivity analysis, lvPPA patients showed decreased connectivity from the seed to the left inferior frontal gyrus (IFG), left inferior temporal gyrus (ITG), medial thalamus, and posterolateral cerebellum. The lvPPA group also showed increased connectivity to motor and somatosensory cortices.
Conclusions:
As hypothesized, lvPPA participants showed lower connectivity to regions within the posterior temporal language network (including L IFG and ITG) compared with HC. Their higher connectivity to motor and somatosensory cortex may suggest compensatory recruitment. This pilot study forms the groundwork for future studies investigating task-based functional connectivity in lvPPA.