ABSTRACT
We explored relationships between decline in cognitive processing speed (CPS) and change in frontal lobe MRI/MRS-based indices of cerebral integrity in 38 healthy adults (age 57-90 years). CPS was assessed using a battery of four timed neuropsychological tests: Grooved Pegboard, Coding, Symbol Digit Modalities Test and Category Fluency (Fruits and Furniture). The neuropsychological tests were factor analyzed to extract two components of CPS: psychomotor (PM) and psychophysical (PP). MRI-based indices of cerebral integrity included three cortical measurements per hemisphere (GM thickness, intergyral and sulcal spans) and two subcortical indices (fractional anisotropy (FA), measured using track-based spatial statistics (TBSS), and the volume of hyperintense WM (HWM)). MRS indices included levels of choline-containing compounds (GPC+PC), phosphocreatine plus creatine (PCr+Cr), and N-acetylaspartate (NAA), measured bilaterally in the frontal WM bundles. A substantial fraction of the variance in the PM-CPS (58%) was attributed to atrophic changes in frontal WM, observed as increases in sulcal span, declines in FA values and reductions in concentrations of NAA and choline-containing compounds. A smaller proportion (20%) of variance in the PP-CPS could be explained by bilateral increases in frontal sulcal span and increases in HWM volumes.
Subject(s)
Cognition/physiology , Frontal Lobe/anatomy & histology , Frontal Lobe/physiology , Aged , Aged, 80 and over , Anisotropy , Aspartic Acid/analogs & derivatives , Aspartic Acid/metabolism , Choline/metabolism , Creatine/metabolism , Female , Humans , Magnetic Resonance Imaging , Magnetic Resonance Spectroscopy , Male , Middle Aged , Nerve Fibers, Myelinated/physiology , Neuropsychological Tests , Organ Size , Phosphocreatine/metabolism , Time FactorsABSTRACT
The chemical composition of a poly(benzoxazine) thermoset polymer (a copolymer of bisphenol-A benzoxazine and tert.-butylphenol benzoxazine) has been studied by pyrolysis-gas chromatography (Py-GC). Major pyrolysates have been identified and the possible degradation pathways have been investigated. A specific pyrolysate was identified for quantitative analysis after carefully proving the linear relationship between the pyrolysate signal intensity and monomer concentration over a wide range of compositions. A method to determine the concentration of the monomer that potentially acts as a cross-linking unit has been developed. In this study, Py-GC was shown to be an excellent analytical technique for the qualitative and quantitative analysis of thermoset polymers.
