White matter disconnection is related to age-related phonological deficits

Abstract

Older adults have more language production difficulties than younger adults but display largely comparable language comprehension abilities. The Transmission Deficit Hypothesis suggests that production difficulties stem from an age-related increase in phonological signal transmission failures, while the semantic system, being more redundant than the phonological system, allows comprehension to be relatively preserved despite signal failures. Though the neural instantiation of the Transmission Deficit Hypothesis remains an open question, white matter represents one important factor to investigate. Metrics indicative of white matter connectivity across the brain, namely, Radial Diffusivity (RD) and Fractional Anisotropy (FA) have also been linked to age-related cognitive differences including naming difficulties. Using a Picture-Word Interference (PWI) task with 18 younger and 19 older healthy adults, we found that, across ages, better picture naming in the presence of phonological distractors was associated with lower RD across dorsal (r = −.35, p = .03), ventral (r = −.34, p = .04), and fronto-striatal (r = −.33, p = .04) tracts, and higher FA along dorsal tracts (r = .43, p = .008). The pattern of lower RD and higher FA, which is thought to reflect better white matter structure, points to the dorsal stream tracts as critical for performance on the PWI task. Moreover, the effects of RD and FA on performance were attenuated by the effect of age, reflecting the shared variance between age and white matter as it relates to language production ability.

Correlations between Dual-Pathway White Matter Alterations and Language Impairment in Patients with Aphasia: A Systematic Review and Meta-analysis

“…Our analysis revealed that mean age moderated the FA-naming correlation of the left superior longitudinal fasciculus and sex influenced the correlation with comprehension. Similar results were reported by recent studies showing that age attenuated the FA-naming association of dorsal tracts (Troutman & Diaz, 2019) and that there were sex differences in FA-comprehension correlations (Jung et al, 2019). However, these statistical findings should be interpreted with caution, considering the underlying neural mechanism remains uncertain.…”

Differences in Diffusion Tensor Imaging White Matter Integrity Related to Verbal Fluency Between Young and Old Adults

“…In addition, the significant increase in RD on the ACR signifies an age-related demyelination effect of that tract, based on previous animal and human studies investigating RD and its relationship to neural networks ( Song et al, 2002 , 2003 , 2005 ; Nair et al, 2005 ; Budde et al, 2007 ), as well as evidence supporting typical aging is accompanied by myelin damage and loss ( Peters, 2002 ). Our study did not find any association between ACR and VF, but Troutman and Diaz (2020) observed that higher RD across dorsal, ventral, and fronto-striatal tracts was associated with poorer performance on a naming with distractors task, suggesting that demyelination can result in poorer language performance.…”

“… Houston et al (2019) reported the performance on a word-retrieval task was associated with increased FA within the inferior fronto-occipital fasciculus (IFOF), in addition to the SLF, and observed increased FA within the corpus callosum that was associated with lower VF scores. Troutman and Diaz (2020) observed among all adult age groups that better performance on a naming with distractors task was associated with lower RD across dorsal, ventral, and fronto-striatal tracts as well as higher FA along dorsal tracts but was unable to find an association when covarying for age groups. Teubner-Rhodes et al (2016) looked at age-related performance in acquisition and retrieval of lexical and semantic information and found age-related declines in arcuate fasciculus (AF) microstructure were related to cognitive processing speed, but not to vocabulary retrieval.…”

“…The lack of associations could have been a result of our small sample size and repeating this study with a larger population could elucidate more findings. While LDH is sensitive to diffusion properties among neighboring voxels and offers complementary information to FA, MD, and RD, for this study, it is possible that the metric is not as sensitive to the brain aging process ( Sullivan et al, 2001 ; Pfefferbaum et al, 2005 ; Sullivan and Pfefferbaum, 2006 ; Westlye et al, 2010 ; Lamar et al, 2014 ; Madhavan et al, 2014 ; Houston et al, 2019 ; Troutman and Diaz, 2020 ).…”

Cerebral White Matter Mediation of Age-Related Differences in Picture Naming Across Adulthood

“…These tracts include the superior longitudinal fasciculus-III (Houston et al, 2019;SLF, White Matter Mediation in Picture Naming, page 5 Madhavan et al, 2014;Stamatakis et al, 2011;Troutman & Diaz, 2019), the inferior longitudinal fasciculus (ILF, Kantarci et al, 2011;Stamatakis et al, 2011;Troutman & Diaz, 2019), and the frontal aslant tract (FAT, Catani et al, 2013;Rizio & Diaz, 2016;Troutman & Diaz, 2019). It is important to note that there are several models of these tracts (for reviews, see Dick et al, 2014;Dick & Tremblay, 2012;Friederici, 2009Friederici, , 2012Varriano et al, 2020).…”