Executive functioning affects verbal learning process in multiple sclerosis patients: Behavioural and imaging results

Verbal learning and memory deficits are among the most frequent in people with multiple sclerosis (pwMS) and have been shown to be affected by deficits in other cognitive domains, such as information processing speed and executive functioning (EF). In the present study, we aimed to further investigate the differential impact that EF may exert on verbal learning and memory on both behavioural and neural levels. Seventy pwMS were assessed with a comprehensive battery of neuropsychological tests, including tests of verbal memory (Selective Reminding Test; SRT) and EF (Stroop test; Phonemic and Alternate Verbal Fluency; Modified Five-Point Test). Structural 3Tesla magnetic resonance imaging (MRI) scans were available for 68 patients; cortical thickness of several frontal, pre-frontal, and hippocampal regions was calculated. Multivariable linear regression analysis showed that patients' performance on Alternate Fluency Test predicted both their immediate (SRT-LTS: R2 =.38; p '.001; SRT-CLTR: R2 =.42; p '.001) and delayed (SRT-D: R2 =.39; p '.001) verbal memory performance. In addition, we found a significant relationship between the cortical thickness of the hippocampus and several bilateral frontal areas (i.e., anterior cingulate gyrus, superior and inferior frontal gyrus, medial frontal cortex, and frontal pole) with verbal memory tests scores (SRT-LTS: R2 =.45; p '.001; SRT-CLTR: R2 =.52; p '.001; SRT-D: R2 =.49; p '.001). These behavioural and MRI results suggest that EF significantly impacts verbal memory performance in pwMS. The understanding of the complex interaction between these distinct cognitive domains can help foster the development of memory rehabilitation paradigms that take into account also the role of executive functioning.