(Sec. 3) What is the Gate Control Theory of pain? (a) What does it mean for the gate to be open or closed?  (b) What factors close and open the gate?  (c) Pick one piece of evidence that is problematic for the traditional physiological view of pain and explain how the Gate Control Theory can account for that evidence. (d) Finally, mention one implication that the Gate Control Theory has for pain control.
 

Gate Control Theory is the leading theory of pain perception.  (Well, actually, neuromatrix theory is a more modern update to GCT, but it is the precursor to this modern theory.)  According to GCT, there is a gate located in the spinal cord.  The gate received input from different sources that serve to open or shut the gate.  When the gate is shut, pain perception is blocked (even if a noxious stimulus is present).  When the gate is open, pain perception is facilitated (sometimes even if no noxious stimulus is present).  [4 pts for explaining open/closed] One source of input to the gate comes from small nerve fibers (the A-delta and C fibers) that conduct pain sensation.  Input from small fibers opens the gate.  A second source of in put to the gate comes from large nerve fibers (A-beta fibers) which carry information about touch.  Input from large fibers serves to close the gate and block pain.  A third source of input to the gate is top-down messages from the brain in the form of emotions, expectations, attention, etc.  Top-down messages of the right sort also serve to close the gate and block pain. [6 pts for explaining the three inputs]

The traditional physiological view of pain has trouble with any evidence that indicates the magnitude of the perceived pain is out of proportion to the extent of the tissue damage.  The most extreme example of this is phantom limb pain where the person experienced pain in a limb that no longer exists because it has been amputated (thus, not tissue damage—in fact no tissue—at the site where pain is experienced).  Other pieces of evidence that you could discuss here include referred pain (pain experienced in a different location from the tissue damage), neuralgia (extreme pain from mild stimulation), causalgia (pain at the site of any old injury, now healed), cultural effect on pain perception such as couvade (male pain during childbirth) or religious rituals that involve physical trauma but are experienced with ecstasy, or any case in which the pain experience does not correspond to the extent of tissue damage (e.g., Beecher’s example of hospitalized soldiers with severe war injuries reporting less pain than civilians with minor injuries).  GCT explains all of this evidence by means of top-down messages from the brain.  Expectations or cognitive appraisal of the situation as positive or meaningful can cause a physically noxious stimulus to be perceived as not (very) painful (e.g., soldier example, hook-hanging ritual).  Conversely, expectations or cognitive appraisal of the situation as negative or fearful can cause a mild stimulus to be perceived as very painful (e.g., causalgia, neuralgia, couvades, and maybe phantom limb pain).  Phantom limb pain is especially suggestive of a central role for the brain in pain perception since it appears that the brain experiences pain in the absence of stimulation of the perceived body part.  One explanation is that the brain as reorganized so that mild stimulation from another part of the body is perceived as painful stimulation from the now-amputated limb. [3 pts for presenting one piece of evidence and 3 pts for explaining how GCT accounts for it.]

The implications of GCT for pain control include any technique for closing the gate.  One category of examples would be to use counter-irritation (e.g., TENS, acupuncture) to stimulate large fibers and close the gate.  A second category of examples would be to exploit top-down messages from the brain to close the gate.  These could include attentional techniques to draw attention away from the distressing aspects of the pain toward the sensory aspects or a non-pain aspect, interpreting the pain experience to be meaningful or positive (e.g., with religion or culture), or using reinforcement to discourage pain behavior and encourage alternate behavior. [4 pts for presenting one implication for pain control.]
 

Note:  This “ideal answer” is much longer than a student answer is expected to be because I tried to list all possible examples of evidence and implications that a student might mention, whereas the student need only present one of each.
 
 

(Sec 2) The ADVANCE study examined the effect that advance directives had on surrogates' predictions about patients' preferences. (a) Explain what an instructional advance directive is. (b) Briefly describe the design of the ADVANCE study. (c) What did the study reveal about the effect of advance directives on family members’ decisions on behalf of the patient?  (c) Discuss at least one possible reason for this finding.

An instructional advance directive is a written statement of a patient’s preferences for medical care intended to guide medical care for the patient in the event that she can no longer make decision on her own behalf.  The purpose of an AD is preserve patient autonomy.  This goal requires that surrogate decision makers (family members and clinicians) need to be able to use the AD to predict accurately what the patient would want in a specific clinical situation.  The purpose of the ADVANCE study (Advance Directives, Values Assessment, aNd Communication Enhancement) was to assess whether ADs improve the accuracy with which family members predict patient preferences. [3 pts for defining instructional directive.]

The participants in this study were older adults and their appointed family member surrogates.  There were four experimental conditions and 1 control condition. The four experimental conditions were the result of a 2x2 design in which there were two types of ADs that the patient would write, and the patient would either discuss or not discuss their AD responses with the surrogate. In the control condition the patient did not write an AD.  In all conditions, after the patient wrote the AD (or not, in the control condition), s/he would complete a questionnaire consisting of 9 medical scenarios. In each scenario the patient indicated whether s/he would want each of 4 medical treatments, if medically indicated.  Then the surrogate read the patient’s AD (or not, in the control condition) and then completed the same questionnaire with 9 medical scenarios.  Surrogates tried to guess the patient’s responses to the scenarios.  The dependent measure was the percent agreement between the surrogate’s predictions and the patient’s actual preferences.  [Note: it is not necessary to describe the part of the study that involved physicians predicting the patients’ preferences.] [6 pts for describing the study design.]

The main result of the ADVANCE study is that ADs did not improve surrogate accuracy in predicting patient preferences.  That is, none of the four experimental groups performed better than the control group, and there were no significant differences among the four experimental groups.  The only effect that ADs had on family member surrogate decisions was to increase the surrogates’ satisfaction with their decisions.  [Although it is not necessary to include this, you might also mention that one type of AD did improve prediction accuracy among doctors who knew nothing about the patient other than what was in the AD.  For primary care docs who knew the patient, ADs had no effect.]  [6 pts for describing the study results.]

There are a number of possible reasons for this lack of effect that you might mention.  One is that family member surrogates knew the patients so well (40 years on average) that the ADs added nothing to what they already knew about the patient’s preferences.  This account can’t explain why accuracy was only about 75%, however.  Another reason is the surrogates are faced with a difficult transfer task where they have to take information in one form (in the AD) and apply it to a new situation (the questionnaire scenarios).  Other psychological research indicates that transfer tasks often yield poor performance.  Still another reason is that the surrogates were using a projection strategy where they used their own preferences as a guide to predicting the patient preferences.  Evidence for projection is that surrogate predictions were more highly correlated with their own preferences than with the patient’s preferences.  Projection is a reasonable strategy for cases where the surrogate is unsure of the patient’s preferences, but it does not respond to the information in the AD and could therefore explain the null findings.  A final reason you might list is that the ADs perhaps did not contain any useful information.  That is, it may be the case that there was little information in the ADs that would help anyone predict the patient’s scenario responses. [5 pts. for listing one plausible reason for the null findings.]