Modeling ketamine effects on synaptic plasticity during the mismatch negativity.

Area of Science:

• Neuroscience
• Psychopharmacology
• Computational Psychiatry

Background:

• Mismatch negativity (MMN) is an electrophysiological response sensitive to auditory changes.
• Ketamine, an NMDA-receptor antagonist, is known to affect MMN amplitudes.
• Existing MMN theories involve neuronal adaptation and predictive coding mechanisms.

Purpose of the Study:

• To investigate the specific mechanisms by which ketamine reduces MMN amplitudes.
• To differentiate the roles of neuronal adaptation and synaptic plasticity in ketamine's effects on MMN.
• To link model-based estimates of ketamine's neurophysiological effects to cognitive outcomes.

Main Methods:

• Applied dynamic causal modeling (DCM) and Bayesian model selection to EEG data.
• Utilized data from a cross-over, double-blind, placebo-controlled ketamine study.
• Employed a predictive coding framework to unify MMN theories.

Main Results:

• Replicated findings that both adaptation and short-term plasticity are essential for MMN generation.
• Identified significant ketamine effects on synaptic plasticity, but not adaptation.
• Observed a selective ketamine effect on the forward connection from the left auditory cortex to the superior temporal gyrus.
• Found that model-based estimates of ketamine's effects on synaptic plasticity correlated with cognitive and control impairments.

Conclusions:

• Ketamine's reduction of MMN is primarily mediated by effects on synaptic plasticity, not adaptation.
• The study proposes a specific neurophysiological mechanism for ketamine's impact on MMN.
• This modeling approach demonstrates the potential for inferring synaptic function and drug modulation from EEG data.