Glutamatergic correlates of gamma-band oscillatory activity during cognition: A concurrent ER-MRS and EEG study

Highlights

• Evoked gamma-band activity changes in response to both object and abstract stimuli.

• Glutamate levels in the LOC differ in response to distinct visual stimuli.

• Glutamate levels correlate with concurrently measured gamma-band oscillatory power.

• ER-MRS can quantify neurochemical concentration changes related to the EEG signal.

Abstract

Frequency specific synchronisation of neuronal firing within the gamma-band (30–70 Hz) appears to be a fundamental correlate of both basic sensory and higher cognitive processing. In-vitro studies suggest that the neurochemical basis of gamma-band oscillatory activity is based on interactions between excitatory (i.e. glutamate) and inhibitory (i.e. GABA) neurotransmitter concentrations. However, the nature of the relationship between excitatory neurotransmitter concentration and changes in gamma band activity in humans remains undetermined. Here, we examine the links between dynamic glutamate concentration and the formation of functional gamma-band oscillatory networks. Using concurrently acquired event-related magnetic resonance spectroscopy and electroencephalography, during a repetition-priming paradigm, we demonstrate an interaction between stimulus type (object vs. abstract pictures) and repetition in evoked gamma-band oscillatory activity, and find that glutamate levels within the lateral occipital cortex, differ in response to these distinct stimulus categories. Importantly, we show that dynamic glutamate levels are related to the amplitude of stimulus evoked gamma-band (but not to beta, alpha or theta or ERP) activity. These results highlight the specific connection between excitatory neurotransmitter concentration and amplitude of oscillatory response, providing a novel insight into the relationship between the neurochemical and neurophysiological processes underlying cognition.