Neurophysiological Targets for Cognitive Training in Schizophrenia

Visual P300 was measured in a 3-stimulus target detection task with target stimuli (10%; large circle) presented in pseudo random order amidst a series of novel (10%; fractal), and standard (80%; small circle) images on a 24" LCD monitor at 100cm viewing distance. Subjects are instructed to press a reaction time button with the preferred hand to Targets only, giving equal importance to speed and accuracy. Primary analysis are based on Target "P300b" identified as the most positive amplitude deflection within the window of 250-550ms post stimulus at posterior midline electrode Pz. The P300b component is thought to reflect cognitive processes involved in memory updating and decision making. P300 reported as difference scores from baseline with negative values indicating increased P300.

Auditory MMN is a fronto-central, mid-latency, potential generated by the auditory cortex in response to deviation in a repetitive stimulus sequence. MMN was assessed using a 3-deviant paradigm in which a series of standard tones (633 Hz, 50ms duration,90%) is interrupted by deviants (10%) that differ either by (1) pitch (1000Hz, 50ms), (2) duration (633 Hz, 100ms), or (3) both (1000Hz, 100ms). MMN was tested concurrently with Visual P300 using a combined task in which subjects were instructed to ignore the auditory stimuli and focus on the visual stimuli. MMN is scored by subtracting each deviant ERP waveform from the standard waveform and measuring the most negative deflection in a window of 50 to 265ms post-stimulus from the resulting difference wave. Primary analysis is based on the combined deviant condition scored at the frontal midline (Fz) electrode site. MMN reported as difference scores from baseline with positive values indicating increased MMN.

The Cognitive Composite score is derived from the MATRICS Consensus Cognitive Battery (MCCB). The MCCB consists of 10 tests and provides standard scores for each according to seven cognitive domains: (1) speed of processing, (2) attention/vigilance, (3) working memory (verbal and visual), (4) verbal learning, (5) visual learning, (6) reasoning and problem solving, and (7) social cognition. The primary dependent measures derived from the MCCB for purpose of this study is the cognitive composite score, computed as the average of standard (t-scores) scores from each domain excluding social cognition. MCCB Composite reported as difference scores from baseline with negative values indicating higher test performance.

The visual learning domain of the MCCB is assessed using the Brief Visuospatial Memory Test-Revised (BVMT-R). In three Learning Trials, the respondent views a stimulus display for 10 seconds and is then asked to draw as many of the figures as possible in their correct location on a page in the response booklet. Scores represent overall accuracy across the three trials, with higher scores indicating better learning. Analysis is based on age- and gender-corrected t-scores. BVMT-R reported as difference scores from baseline with negative values indicating higher test performance.

The verbal learning domain of the MCCB is assessed using the Hopkins Verbal Learning Test-Revised (HVLT-R). In three Learning Trials, the respondent listens to a 12-item word list read by an examiner and is then asked to recall as many of the words as possible from memory. Scores represent overall accuracy across the three trials, with higher scores indicating better learning. Analysis is based on age- and gender-corrected t-scores. HVLT-R reported as difference scores from baseline with negative values indicating higher test performance.

Visual working memory is assessed in the MCCB using the Spatial Span task of the Wechsler Memory Scales-III. Using a board on which 10 cubes are irregularly spaced, the examiner taps patterns of increasing length. The respondent is asked to follow by tapping the pattern in the same or reverse sequence. Scores represent total accuracy combined over forward and reverse span conditions. Analysis is based on age- and gender-corrected t-scores. Spatial Span reported as difference scores from baseline with negative values indicating higher test performance.

Auditory working memory is assessed in the MCCB using the Letter-Number Sequencing (LNS) task. LNS is an orally administered test in which and examiner reads strings of numbers and letters, of increasing length over trials, and the respondent mentally reorders the string and reports back to the examiner verbally. Scores represent total number of accurate trials. Analysis is based on age- and gender-corrected t-scores. LNS reported as difference scores from baseline with negative values indicating higher test performance.