Multimodal Assessment of Neurological Function

The event-related potential and MRS methods have been described previously,^{33 ,36 (link),52 (link)} and details are given in the eMethods in the Supplement. Briefly, the event-related potential was recorded using a 64-channel system^{2 (link)} (SynAmps; Compumedics Neuroscan) at a 1-kHz sampling rate with bandpass at 0.1 to 200 Hz. The paradigm was a passive duration-deviant odd-ball task.^{52 (link)} Standard and deviant trials were averaged separately, followed by subtraction of the 2 mean waveforms. Mismatch negativity was scored by peak detection within a poststimulus window of 100 to 225 milliseconds by an automatic algorithm, followed by visual inspection to verify correct placement of each marker for peak detection. Magnetic resonance scanning was conducted on a 3-T imaging system (Tim Trio; Siemens) equipped with a 32-channel head coil. Spectra were acquired with a short-echo sequence for detection of glutamatergic measures^{36 (link)} and a spectral editing sequence for detection of GABA with minimal macromolecule contamination.³³ Metabolites were quantified with available tool kits (LCModel; LCModel Inc^{53 (link)} and freely available GANNET^{54 (link)}) and corrected for the proportion of voxel gray, white, and cerebrospinal fluid tissue proportions^{55 (link)} and then reported in institutional units (Table 2). Figure 1 shows voxel location, representative spectra, and MMN waveforms.