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Glutamate and laser evoked potentials : the role of the cingulate cortex Choles, Cassandra


Laser evoked potentials (LEPs) provide an avenue to discern individual differences in nociception, to further understand pain perception. We aimed to investigate resting neurobiological differences that may contribute to the small and large responses to noxious laser stimulation in 50 participants (26 females). To do this, participants underwent a two-part protocol. First, LEPs and verbal pain ratings were collected at four different laser intensities, and the resultant signal amplitudes (N1, N2, and P2) were clustered, forming two respective groups for each LEP outcome of small vs. large signal amplitudes, as well as high vs. low pain ratings. Next, participants underwent a magnetic resonance spectroscopy (MRS) scan to measure excitatory glutamatergic activity within the cingulate cortex at rest in four regions: the anterior (ACC), anterior-mid (aMCC), posterior-mid (pMCC), and posterior (PCC) cingulate cortices. Glutamatergic activity (glutamate, glutamine, and combined (Glx)) was compared between each respective cluster across the four cingulate regions, with sex included as a covariate for glutamine specifically. We found three key findings: 1) Resting glutamatergic activity was significantly higher in anterior vs. posterior regions. 2) Participants with higher verbal pain ratings had significantly higher glutamate concentrations in the ACC. 3) Participants with larger P2 amplitudes had significantly higher glutamate concentrations in the PCC. These findings contribute to our knowledge and understanding of glutamatergic activity in the cingulate cortex at rest. Specifically, that pain ratings and P2 amplitudes (reflecting attention) are not equivocal, although they are both influenced by differences in regional cingulate activity, suggesting the involvement of the ‘hubs’ of the salience and default mode networks through the ACC and PCC, respectively. Further research expanding on our sample size, brain regions, metabolites investigated, and LEPs conditions will assist in further understanding the intrinsic neurobiological differences to provide further insight into different responses to nociception and pain.

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