Verbal memory deficits are present in multiple sclerosis (MS), but neither inflammatory T2 lesion volume nor cerebral atrophy (generalized or localized hippocampal atrophy) fully explain disease-related verbal memory changes. Importantly, the hippocampus does not function in a vacuum; memory encoding and retrieval requires interactions between the hippocampus and cortical areas where information is processed and represented. Indeed, we have previously shown that lexical access speed (a language function assessed by rapid automatized naming) independently predicted delayed recall of verbal information (word list) for persons with MS, even when controlling for total learning. Informed by this work and recent ultra high field (7.0 Tesla) MRI research reporting high cortical lesion count in regions associated with phonological processing (e.g., plenum temporale, superior temporal gyrus), we assessed whether phonological processing independently explains verbal memory deficits in persons with MS.

Analyses were performed on a clinical sample of persons withMS aged 18 to 59 years (n=60: 49 relapsing, 11 progressive). Word-list memory was assessed by the Hopkins Verbal Learning Test, Revised (HVLT-R), which yielded scores for Total Learning (TL) and Delayed Recall (DR). Phonological processing was assessed with WIAT-4 Phonemic Proficiency. WIAT-4 Sentence Repetition was utilized as a non-phonological language control task, and WIAT-4 Word Reading was administered to control for premorbid verbal ability. CANTAB Paired Associate Learning served as a nonverbal memory comparison. Performance on tasks was standardized using published age-adjusted norms. Primary analyses used partial correlations to assess relationships between Phonemic Proficiency and (a) HVLT-R TL and DR controlling for WIAT-4 Word Reading, and (b) HVLT-R DR controlling for WIAT-4 Word Reading and HVLT-R TL. To assess specificity to phonological processing, the same partial correlations assessed relationships between Sentence Repetition and HVLT-R variables, and between Phonemic Proficiency and nonverbal memory (CANTAB PAL).

When controlling for premorbid verbal ability, Phonemic Proficiency performance accounted for 7.8% of the variance in HVLT-R TL (rpartial=0.28, p=0.031) and 16% of the variance in HVLT-R DR (rpartial=0.40, p=0.002). Moreover, when additionally controlling for HVLT-R TL, Phonemic Proficiency still accounted for 10% of the variance in HVLT-R DR (r partial— 0.32, p=0.016). Showing specificity to phonological processing ability, performance on Sentence Repetition was not significantly related to HVLT-R DR when controlling for premorbid verbal ability (WIAT-4 Word Reading) and HVLT-R TL (rpartial=0.09, p=0.510). Showing specificity to verbal memory, neither Phonemic Proficiency nor Sentence Repetition performance were reliably related to CANTAB PAL for any variance in performance in nonverbal memory (Ps>0.9).

Results suggest that language ability, specifically phonological processing, contributes to delayed recall of word lists independent of premorbid verbal ability and initial total learning scores in persons with MS. These findings demonstrate contributions of language ability to verbal memory and highlight the need for further research into language ability changes in persons with MS. This may have implications for verbal memory rehabilitation in MS.