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Impaired LTP-like visual cortical plasticity in schizophrenia: An EEG time-frequency analysis
Impaired neuroplasticity is implicated in the pathophysiology of schizophrenia (SZ). Long-term potentiation (LTP), a form of synaptic plasticity, has been demonstrated in humans by showing that repeated visual stimulation results in enhanced EEG-based visual evoked potentials (VEPs). We previously showed that high frequency stimulation (HFS) produced sustained VEP potentiation in healthy controls (HC), but not in SZ. We extend this work by examining EEG oscillatory activity following HFS. VEPs were elicited by a checkerboard stimulus (∼.83Hz, 2-min blocks) before and after exposure to visual HFS (∼8.8Hz, 2 min) in 19 SZ and 21 HC. A permutation testing approach was applied to time-frequency data to examine LTP-like effects. A mixed model of mean inter-trial coherence (ITC) of phase in the identified cluster (0-496ms, dominated by theta activity at occipital electrodes) showed a Group x Time interaction; mean ITC was enhanced in HC compared to SZ at early post-stimulation blocks relative to baseline. A mixed model of mean total power in its cluster (0-450ms, theta activity only) revealed a Group x Time interaction; total power was enhanced in HC but not SZ across post-stimulation blocks. Visual HFS enhanced theta power and phase consistency in HC only, demonstrating LTP-like plasticity alterations in SZ.