Research Description:

EFFECTS OF MTBI ON PAIN PERCEPTION IN HUMANS

The purpose of this project is to determine whether differential MTBI-related effects on the subsystems of pain modulation can be demonstrated. Our study design is based (1) upon the idea that pain sensitivity can be inferred from the pain intensity reported by the subject in response to brief individual stimuli, and (2) upon the assumption that prolonged stimuli produce a different pain intensity than brief stimuli of the same physical magnitude because they allow time for feedback modulation. Thus, the difference in reported pain intensity of a brief vs. a long stimulus may serve as a measure for the activity of feedback modulation. To begin the study, healthy human subjects were tested to collect and analyze the control data.

Our first specific aim is to probe pain sensitivity with a test protocol that uses brief stimuli. Our second specific aim is to challenge feedback modulation systems with prolonged experimental stimuli in order to demonstrate whether mild brain injury can alter the rate with which pain sensitivity changes in the presence of prolonged nociceptive inputs. Our third specific aim is to gain insight into whether or not brain injury affects C-fiber mediated nociceptive inputs and inputs traveling through the faster conducting A-fibers in a different manner.

The two areas under study will undergo a series of tests with the duration of the focal thermal contact ranging from one second to twelve seconds with a thirty second interval between stimuli. The 23x23mm flat metal thermode will always start at a low temperature of 43 deg C for the first stimulus and then incrementally increase from stimulus to stimulus until a pain intensity level of 45% is reached. At that point, the temperature will begin to decrease stepwise until pain is no longer felt. These data will give rise to a stimulus-response function from which pain sensitivity can be inferred.