Laser-evoked potential P2 single-trial amplitudes covary with the fMRI BOLD response in the medial pain system and interconnected subcortical structures

Pain is a complex experience with sensory, emotional and cognitive aspects. The cortical representation of pain - the pain matrix - consists of a network of regions including the primary (S1) and secondary (S2) sensory cortex, insula, and anterior cingulate cortex (ACC). These structures interact with brain regions such as the prefrontal cortex and the amygdalae. Simultaneous EEG/fMRI (electroencephalography/functional magnetic resonance imaging) has recently been introduced as a method to study the spatiotemporal characteristics of cognitive processes with high spatial and high temporal resolution at the same time. The present study was conducted to clarify if single trial EEG-informed BOLD modeling supports the definition of functional compartments within the pain matrix and interconnected regions. Twenty healthy subjects received painful laser stimulation while EEG and the fMRI blood oxygen level dependent (BOLD) signal were recorded simultaneously. While the laser-evoked N2 potential provided no additional information for BOLD modeling, the regressor obtained from the single trial laser-evoked P2 potential explained additional variance in a network of cortical and subcortical structures that largely overlapped with the pain matrix. This modeling strategy yielded pronounced activation in the ACC, right amygdala and thalamus. Our results suggest that laser-evoked potential (LEP) informed fMRI can be used to visualize BOLD activation in the pain matrix with an emphasis on functional compartments (as defined by the temporal dynamics of the LEP) such as the medial pain system. Furthermore, our findings suggest a concerted effort of the ACC and the amygdala in the cognitive-emotional evaluation of pain.