Mismatch negativity reveals plasticity in cortical dynamics after 1-hour of auditory training exercises

Background: Impaired sensory processing contributes to deficits in cognitive and psychosocial functioning in individuals with schizophrenia (SZ). Mismatch Negativity (MMN), an event-related potential (ERP) index of sensory discrimination associated with cognitive and psychosocial functioning, is a candidate biomarker of auditory discrimination and thus possibly of changes following auditory-based Targeted Cognitive Training (TCT). Here we evaluated the acute effect of TCT on cortical processes supporting auditory discrimination. Methods: MMN was assessed in 28 SZ outpatients before and after a single 1-hour (hr) session of "Sound Sweeps," a pitch discrimination task that is a component of the TCT suite of exercises. Independent component (IC) analysis was applied to decompose 64-channel scalp-recorded electroencephalogram (EEG) activity into spatiotemporally stationary sources and their activities. ICs from all patients were pooled to find commonalities in their cortical locations. IC cluster-mean ERPs were evaluated to determine the clusters contributing to the (140-200 ms) MMN difference between responses to deviant and standard tone stimuli respectively. Results: Two frontal IC clusters centered in orbitofrontal cortex (OFC) and anterior cingulate cortex (ACC) accounted for > 77% of MMN variance across all scalp channels. After 1-hr auditory training, significant suppression of ACC cluster contributions was detected, whereas the OFC cluster contribution was unchanged. Conclusions: Prior to TCT, the MMN response was dominated by EEG effective sources in or near OFC and ACC. However, after 1-hr of auditory-based TCT, a significant attenuation of ACC was observed, whereas OFC contribution to MMN persisted. The present findings support further trials designed to test whether training-related MMN plasticity in the ACC after 1-hr may predict individual patient response to a full course of TCT.