N-acetylaspartate and creatine levels measured by H-1 MRS relate to recognition memory

Objectives: To investigate the relationship between recognition memory and metabolite levels in medial structures of the temporal lobes in the living human brain. Methods: Proton MRS (H-1 MRS) and the intracarotid amobarbital test were performed in 16 epileptic patients found suitable for temporal l obectomy. All patients had mesial temporal sclerosis. Metabolite ratios bet ween N-acetylaspartate (NAA), creatine and phosphocreatine (Cr + PCr), and choline-containing compounds (Cho) [NAA/(Cr + PCr), NAA/Cho, and NAA/(Cr PCr + Cho)] were calculated for H-1 MRS voxels that included the amygdala, anterior half of the hippocampus, and underlying subiculum. Metabolite rati os were correlated with unilateral memory scores estimated by the intracaro tid amobarbital test for words, objects, faces, and total score. Results: T he total memory score, memory for objects and faces, and NAA/(Cr + PCr) wer e significantly lower for the hemisphere ipsilateral to the resection. The asymmetry indexes for NAA/(Cr + PCr) correlated with asymmetry indexes for words (rho = 0.82, p = 0.0001) and total memory (rho = 0.72, p = 0.002). An alysis of memory scores and metabolite ratios from all 32 hemispheres revea led a correlation between NAA/(Cr + PCr) and memory for words (rho = 0.45, p = 0.009). A correlation between memory for words and NAA/(Cr + PCr) exist ed in the contralateral (rho = 0.58, p = 0.019) and in the right (rho = 0.5 1, p = 0.045) hemispheres, and a trend was found in the left hemispheres (r ho = 0.48, p = 0.06). Conclusion: There is a correlation between memory for words and the NAA/(Cr + PCr) ratio from medial temporal structures in pati ents with mesial temporal sclerosis. The findings suggest that medial tempo ral structures and adjacent neocortex play a significant role in recognitio n memory in humans, particularly for words.