Poster Session B, Sunday, March 24, 8:00 – 10:00 am, Pacific Concourse
Age differences in hippocampal glutamate modulation during object-location encoding: evidence from proton functional magnetic resonance spectroscopy (¹H-fMRS).
Chaitali Anand1, Dalal Khatib1, Cheryl Dahle2, Jeffrey Stanley1, Naftali Raz2; 1Department of Psychiatry and Behavioral Neuroscience, Wayne State University, Detroit MI, USA, 2Institute of Gerontology, Wayne State University, Detroit MI, USA
Hippocampal glutamate mediates learning and memory and glutamatergic dysfunction may signal age-related cognitive decline. We hypothesized that differences in glutamate modulation during memory encoding underlie age-differences in associative learning and memory. Spectroscopy data were acquired from unilateral hippocampi (randomized across subjects) of thirteen young (age 24±2.3; M=6; F=7) and six old (65±3.5; M=2; F=4) healthy adults during an associative learning and memory task, which involved encoding and cued retrieval of 12 object-location pairs. Twelve encoding-retrieval cycles were interspersed with epochs of counting backwards to foil rehearsal. Associative learning data were modeled using Gompertz function. Outcome variables included learning proficiency over time (slope, asymptote, inflection-point) and glutamate levels acquired during a neutral condition, and across the encoding and retrieval epochs. Old participants attained a lower asymptote [t(17)=1.93, p=.011], and tended to show a later inflection-point of learning [t(17) = 1.85, p=.08], compared to the young. Patterns of glutamate changes over encoding differed between groups: age-group × epoch: F(5,74)=3.96, p=.003. In young adults, a linear increase followed by a linear decrease was observed. Older participants evidenced a steady linear decrease after the initial three trials. In the older but not young adults, higher neutral-condition glutamate was associated with earlier inflection point of the learning curve. Results show altered hippocampal glutamate modulation during memory encoding concomitant with the poorer learning proficiency in old compared to the young. The results suggest a functional role of glutamate in age-related memory decline, without the confounding effects of hemodynamics that limit the validity of fMRI inference.
Topic Area: LONG-TERM MEMORY: Development & aging