Video link @ SUCEDE YouTube Channel
In our latest working session, the SUCEDE research group presented an update on the integrity of inhibitory circuits in patients with psychosis. By combining Transcranial Magnetic Stimulation (TMS) and Electroencephalography (EEG), we are successfully “mapping” the neurochemical balance of the prefrontal cortex with unprecedented precision.
The Challenge: Measuring GABA Non-Invasively
Cortical inhibition, primarily mediated by the GABAergic system, is fundamental for cognitive processing. In pathologies such as schizophrenia and bipolar disorder, it is hypothesized that this system is altered. To measure it, we use two paired-pulse paradigms:
- SICI (Short-interval Intracortical Inhibition): Primarily reflects GABA-A receptor activity.
- LICI (Long-interval Intracortical Inhibition): Linked to GABA-B receptor activity.
Key Findings:
The data presented by Gema Mijancos suggest interesting differences between diagnoses and their relationship to patient functionality:
- LICI Alterations and Cognition: Significant alterations in long-interval intracortical inhibition (LICI) were observed in both early and late windows of the evoked potential. A critical finding is that LICI levels correlate with the subjects’ cognitive performance.
- Differences by Diagnosis: While alterations in schizophrenia appear to extend to later components (such as the P140), results in bipolar disorder show greater variability, possibly influenced by concomitant medication (anticonvulsants and lithium).
- Beyond Diagnosis – Towards Biotypes: The linear regression models presented indicate that clinical diagnosis alone does not predict cognitive performance. However, cortical inhibition markers (especially LICI) do possess significant predictive power. This reinforces the need to classify patients by neurophysiological biotypes rather than traditional diagnostic labels.
Next Steps: Refining the Region of Interest (ROI)
One of the most debated points within the group was the optimization of the Region of Interest (ROI) in the dorsolateral prefrontal cortex. Topographies show that inhibition is not a localized phenomenon but extends across bilateral frontal areas. Redefining these maps will allow us to capture the differences between healthy controls and patients with greater sensitivity.
Conclusion:
This study underscores that neurophysiology through TMS-EEG not only helps us understand the pathophysiology of psychosis but also emerges as an objective tool for predicting cognitive decline, opening the door to more personalized interventions.