Abstract
Working memory declines are common in healthy aging and have been linked to
alterations in both glutamatergic signaling and striatal dopaminergic function. Although prior
multimodal neuroimaging work has demonstrated positive associations between striatal
glutamate and dopamine synthesis capacity in young adults, it remains unclear whether this
neurochemical coupling is preserved in older adults and how it relates to working memory
performance. The present study examined relationships between glutamate (Glx) measured with
magnetic resonance spectroscopy (MRS), dopamine synthesis capacity measured with
[¹⁸F]fluoro-L-m-tyrosine (FMT) positron emission tomography (PET), and working memory
measured as Backward Digit Span performance in 29 healthy older adults (M age = 70.5 years).
We identified a significant positive association between Glx in the left dorsal putamen and
dopamine synthesis capacity in the dorsal caudate. A trend in the same direction was observed
in the dorsal putamen, though it did not reach significance. Neither Glx nor dopamine synthesis
capacity were significantly associated with Backward Digit Span performance, though dopamine
showed a positive trend. Exploratory analyses demonstrated that other MRS-derived measures
(myo-inositol and ascorbate) were positively associated with dopamine synthesis capacity in the
ventral striatum, suggesting regionally specific patterns of neurochemical coupling. These
findings provide preliminary evidence that glutamate-dopamine associations in the striatum are
preserved in healthy aging. Future work with larger samples is needed to clarify the functional
significance of these associations for working memory and motor performance.