Verbal learning in logopenic variant Primary Progressive Aphasia: An EEG investigation

The logopenic variant of PPA (lvPPA) is characterized by impaired single-word retrieval and impaired repetition, which suggests a phonological working memory impairment. Phonological working memory is an essential mechanism for verbal learning; thus, one would expect that the verbal learning skills of this population would be thoroughly investigated. Nonetheless, the relevant research is scarce. As a preliminary investigation aiming to deepen our understanding of verbal learning in lvPPA, we studied how resting-state electroencephalographic (EEG) activity relates to the verbal learning abilities in this group. Specifically, short low-density (i.e., 8 channels, bilaterally) EEG recordings were collected from nine lvPPA individuals at resting-state. Activity at the five frequency bands (delta, theta, alpha, beta, gamma) was extracted and correlated with Sum of Trials performance on the Rey Auditory Verbal Learning Test (RAVLT). Our results showed a statistically significant association between delta band activity and verbal learning across the brain, particularly in the left parietal region. Specifically, higher delta power (on average across channels, as well as at each of the eight channels separately) was associated with lower RAVLT scores. EEG activity at the other frequency bands did not show a statistically significant association with verbal learning. These findings provide the first insights into the association of resting-state electrophysiological activity with verbal learning in lvPPA. The findings of this preliminary investigation can be used as guiding evidence in future neuromodulation studies to target activity at specific frequency bands for electrical stimulation both in lvPPA, as well as in other populations with similar learning impairments.