Introduction: Pattern separation (PS) is a neurocognitive process that is essential
for distinguishing highly similar objects from one another. The dentate gyrus has
been previously considered the primary anatomical and neurofunctional focus of
this central memory process. PS has traditionally been studied in the context of
visual discrimination of highly similar everyday objects. To date, the
neurofunctional substrates of auditory PS have not been investigated, and only
a handful of studies have examined the behavioural age effects on auditory PS.
Methods: The present study adapted the prominent mnemonic similarity task
from Stark et al. (2019) to assess and directly compare both visual and auditory PS
using fMRI. A sample of 46 subjects, 23 per group, aged between 19 and 79 years
of age, completed alternating trials of visual and auditory pattern separation using
non-semantic visual shapes and two-syllabic pseudowords.
Results: Contrary to our expectations, no hippocampal activation was found during
auditory PS. Instead, left-lateralized cortical regions were identified, including the
superior temporal gyrus, the inferior frontal gyrus, and the pre-supplementary motor
area. Furthermore, the older subjects demonstrated age-related deficits in lure
discrimination and recognition memory performance; however, these deficits were
not consistently observed at the neurofunctional level.
Discussion: In sum, the present findings point to a double dissociation between
visual and auditory PS. Furthermore, the results on ageing, both behavioural and
functional, could reflect age-related changes in neurovascular coupling and
declines in visual and auditory perception, as well as methodological challenges
in examining PS across different sensory modalities and age.