The Perception of Pain

Pain Fear Permanent Memory Process in the Brain
Medical researchers at the University of Toronto have identified where emotional fear memory and pain begin. The study, funded by the Canadian Institutes of Health Research, the National Institutes of Health, the EJLB-CIHR Michael Smith Chair in Neurosciences and Mental Health, Canada and published in Neuron, used mice to reveal how receptors activated in the pre-frontal cortex, the area of the brain involved with higher intellectual functions, play a pivotal role in the establishment of fear.

The deep significance of this discovery is that, previously, research had indicated to the activation process beginning in the hippocampus (located in forebrain) as the origin point of fear memory. However, the research team has found that fear memory does not happen right after a painful trauma – it takes some time for the memory to become part of our consciousness. Researchers report that the sequence of events goes like this: The painful experience activates NMDA receptors  (molecules on cells receiving messages and then producing certain physiological effects in the cell), which are normally inactive but are stimulated when the brain registers a shock. Over time, the NMDA receptors leave their imprint on brain cells. After administering shocks to mice, the researchers traced a specific protein (called NR2B), which previously had been thought to be linked with fear memory in the hippocampus and the amygdala.

Professor Min Zhuo, the EJLB-CIHR Michael Smith Chair in Neurosciences and Mental Health, commented, "By identifying NR2B in the pre-frontal cortex of the brain, we propose that fear memory originates from a network of receptors, rather than one simple area. While we know it exists in the hippocampus, amygdala and the pre-frontal cortex, we don't know exactly how it alters them." The next phase to discover, Zhuo speculated, is that by comprehending the biomolecular mechanisms behind fear, doctors will be able to discover therapeutic ways to relieve emotional pain in patients by reducing the capability of traumatic events to be permanently imprinted in the brain.

Red Heads Suffer More Pain

Research presented at a meeting of the American Society of Anesthesiologists reveals that researchers have now discovered (through clinical studies) that individuals with red hair are indeed more sensitive to pain and thus require more anaesthetic during operations than other patients.

The medical research was done at the Outcomes Research Institute of the University of Louisville, Kentucky. A group of 10 red-haired women and 10 dark-haired women were administered a standard inhaled anaesthetic. Following each dose of the anaesthetic, the subjects were given an electric shock and the process was duplicated until the women felt no pain sensation. In addition, the patients’ reflexes were also measured to evaluate the efficiency of the painkiller.

The doctors found that 20% more anaesthetic was required by the red-haired group than the dark-haired group. The underlying cause for this seems to be that, in red-haired individuals, the cells that create skin and hair pigment have a dysfunctional melanocortin 1 receptor, triggering the secretion of a greater quantity of the hormone that stimulates these cells. An associated result of this process is that the hormone also activates a brain receptor associated with pain sensitivity.

The lead anaesthesiologist commented that exploring the function of the melanocortin system in the central nervous system holds promise to further our knowledge as to which brain systems produce unconsciousness and which adjust pain perception.

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Sources: Activation of Erk in the Anterior Cingulate Cortex During the Induction and Expression of Chronic Pain Molecular Pain 2008 Jul 23;4:28 Central Plasticity in Pathological Pain Novartis Foundation Symposium 2004;261:132-45; discussion 145-54 Origins of Fear University of Toronto 15-Sep-2005 (www.eurekalert.org/pub_releases) Women with Red Hair Report a Slightly Increased Rate of Bruising but Have Normal Coagulation Tests Anesthesia-Analgesia 2006;102:313-318 Anesthetic Requirement is Increased in Redheads Anesthesiology 2004 Aug;101(2):279-83