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|LETTER TO EDITOR
|Year : 2021 | Volume
| Issue : 6 | Page : 1853-1854
Do Thresholds for Nociceptive Flexion Reflex and Subjective Pain Coincide?
Srishti Nanda, Suvercha Arya, Renu Bhatia
Pain research and TMS Laboratory, Department of Physiology, All India Institute of Medical Sciences (AIIMS), New Delhi, India
|Date of Submission||08-May-2019|
|Date of Decision||14-Nov-2019|
|Date of Acceptance||14-Nov-2019|
|Date of Web Publication||23-Dec-2021|
Dr. Renu Bhatia
Department of Physiology, Lab Incharge: Pain research and TMS Laboratory, 6007, 6th Floor, Convergence Block, Ansari Nagar, All India Institute of Medical Sciences (AIIMS), New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Nanda S, Arya S, Bhatia R. Do Thresholds for Nociceptive Flexion Reflex and Subjective Pain Coincide?. Neurol India 2021;69:1853-4
Nociceptive flexion reflex (NFR) is an important neurophysiological measure adopted by clinics to assess pain and quantify the effect of an intervention. Classical literature shows that subjective pain experience (SP threshold) coincide with the NFR thresholds in healthy participants, while a disparity exists between the two in chronic pain conditions. Over the years, the observed association of the NFR threshold with SP has affirmed its status as an “objective marker of pain.”
While performing some other planned experiments on pain perception, it was unexpectedly noticed that the NFR threshold did not correspond to the pain experienced by the healthy volunteers, calling for a formal investigation. NFR and SP thresholds were found to be significantly different (mean difference = 19 volts, effect size of difference = 0.6812, P < 0.01; number of participants = 31, number of females = 15, average age = 31.45 ± 8.23 years). NFR and SP thresholds coincided in only three of our subjects. All recordings were done according to the procedure previously described.
The results suggest that the relationship between the NFR threshold and SP may not be as linear as previously reported. A possible explanation of the results maybe because of the basic neurophysiological difference between NFR and SP. Our current belief is that SP is the result of higher-order processing taking place at the different levels of the central nervous system (CNS; cortical and subcortical), while NFR relies more on the nociceptive activation followed by a spinally mediated reflex response. From an anatomical standpoint, nociceptors sense and relay the noxiousness or saliency of the stimulus received, but they are not designed to faithfully transmit the entire repertoire of the pain experience. Therefore, even when the electrical stimulus is high enough to activate the nociceptors, it may or may not be processed or interpreted as a subjective painful sensation. In line with our proposition, a recent set of the reports also portrays NFR as being reflective of wider physiological defence response. Keeping this in mind, two pertinent questions arise. First, could investigation of factors that influence NFR also affect pain perception? Second, could NFR be used to report “resolution from painful state” after an intervention?.
That having been said, a note of caution is due here as robust literature still exists to support the usefulness of NFR in testing the integrity of the circuitry, current state of spinal-excitability, and changes occurring at the supraspinal levels of pain processing. To conclude, our observation raises intriguing questions regarding NFR and could serve as a primer to revisit its physiological interpretation and current applications.
Authors would like to acknowledge contributions of Suman Tanwar and Bhawna Mattoo for data interpretation and Sanjeev Kumar and Suman Pandey for technical support.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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