Impaired Visual Information Processing in Alcohol-Dependent Subjects: A Proton Magnetic Resonance Spectroscopy Study of the Primary Visual Cortex

Abstract

OBJECTIVE: Chronic alcoholism is associated with impaired cognitive abilities, with a more severe deficit in visual than in verbal functions. The visual processing deficits have classically been associated with impaired function of the visual cortex, located in the occipital lobe. The present study sought to increase current understanding of the impaired visual processing abilities in alcohol-dependent subjects and their correlation with metabolic aberrations in the occipital lobe using in vivo proton magnetic resonance spectroscopy (¹H MRS). METHOD: To that end, ¹H MRS was carried out in the primary visual cortex on 35 alcohol-dependent subjects and 35 healthy controls. Neuropsychological tests for visual processing skills were performed on all the subjects, and the deficits were reported as raw dysfunction rating scores. RESULTS: The alcohol-dependent subjects showed a significant increase in choline/creatine (Cho/Cr) and myo-Inositol/creatine (mI/Cr) ratios, whereas N-acetyl-aspartate/creatine (NAA/Cr) and glutamate-glutamine/creatine (Glu-Gln)/Cr ratios were significantly decreased. Reductions in NAA levels might be attributed to neuronal loss, whereas reductions in Glu-Gln levels might reflect perturbation of the Glu-Gln system in alcohol-dependent individuals, which could represent a neuroprotective adaptation. Elevations in mI levels may reflect astrocyte proliferation as well as an osmotic response to cell shrinkage, whereas a significant increase in Cho levels indicates altered cell membrane metabolism. Also, a significant inverse correlation between NAA/Cr and raw dysfunction scores (rDyS) on the Nahor-Benson (NB) test and Glu-Gln/Cr with rDyS of the NB and the Bender-Gestalt (BG) test was observed, whereas a positive correlation between rDyS of the BG and the NB test and Cho/Cr was observed. CONCLUSIONS: The results suggest that metabolic alterations in the primary visual cortex may contribute to the neuropsychological impairment in visual information processing observed in alcohol-dependent subjects.