Pain Sensitivity and Structural Properties of the Medial Forebrain Bundle

Elizabeth Rizzoni, BA
Department of Neurology
Division of Basic Neuroscience Research
Poster Overview

Background: Our bodies send information about our surroundings up to our brains. Then the brain complexly interprets those signals through its own systems of nerves. One such signal that our brain interprets is pain. However, not everyone has the same experience of pain, even when subjected to the same painful stimulus. Utilizing a safe pain experience for in-lab use, MRI brain scans, and participants’ self-reported pain, we studied whether a particular series of connections within the brain (the Medial Forebrain Bundle – MFB) is responsible for people’s variable pain sensitivity.

Methods: 38 healthy male participants underwent MRI brain scans, an established heat-pain paradigm, and rated their pain on a scale from 0 (no pain) to 100 (unbearable pain). MRI data was processed using established methods to focus on characteristics of the MFB’s structure. Relationships between these MFB characteristic measures and participants’ self-reported pain scores were assessed by statistical tests.

Results: Two of three of the MFB characteristics studied correlated significantly with participants’ pain scores.

Conclusions: Correlations between MFB measures and pain scores indicate a relationship between MFB tissue integrity and individuals’ experience of pain. This means that variations in MFB structure may be responsible for people’s variable sensitivities to pain.

Scientific Abstract

Background: The neuromatrix of pain is composed of ascending and descending brain tract systems. While the ascending system relays signals from the body to the brain, the descending system interprets them and may be responsible for humans’ variable sensitivity to pain. A major tract of the descending system is the medial forebrain bundle (MFB). The relationship between pain sensitivity and MFB white matter microstructure was assessed using MRI, pain paradigms, and subjects’ self-rated pain.

Methods: 38 healthy male participants (age: 27.05 ± 5.7yrs; BMI: 18.5-30kg/m2) underwent MRI brain scans (3T-Siemens-Magnetom-Prisma), completed an established heat-pain paradigm, and rated their pain from 0 (no pain) to 100 (unbearable pain). Data was processed, and MFB specific dMRI measurements were extracted (https://github.com/pnlbwh/pnlpipe). Spearman correlations between pain sensitivity ratings and MFB measures (Fractional Anisotropy of Tissue (FAt), Radial Diffusivity of Tissue (RDt), Axial Diffusivity of Tissue (ADt)) were run (R 3.4.1).

Results: Pain ratings correlated positively with RDt (p=0.030), negatively with FAt (p=0.015), and non-significantly with ADt (p=0.886).

Conclusions: Significant correlations between pain sensitivity ratings with RDt and FAt indicate an association of MFB tissue integrity with lower pain sensitivity ratings. This suggests that the MFB may factor in the variability of individuals’ pain sensitivity.

Clinical Implications
This study illustrates the Medial Forebrain Bundle’s (MFB) relationship with individuals’ sensitivity to pain. With increased understanding of our brains’ endogenous modulation of pain signals, clinicians may better anticipate patients’ pain and their risk for pain chronification in future.
Research Areas
Authors
Elizabeth Rizzoni, Maria Geisler, Nikos Makris, Ofer Pasternak, Yogesh Rathi, Sylvain Bouix, Martha E. Shenton, Marco Herbsleb, Karl-Jürgen Bär, Thomas Weiss, Zora Kikinis
Principal Investigator
Dr. Martha E. Shenton

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