Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The pathways of interoceptive awareness Khalsa, SS,* Rudrauf, D,* Feinstein, JS, and Tranel, D. Supplementary Information * These authors contributed equally to this work. Participants The participants were 11 healthy males and patient 1951 (aka ‘Roger’), a rare neurological patient drawn from our patient registry (see Supplementary Table 1 for complete demographics). Roger acquired focal bilateral brain damage following a severe episode of herpes simplex encephalitis in 1980. Briefly, his brain injury involves extensive bilateral damage to the insular, anterior cingulate and orbitofrontal cortices, basal forebrain, hippocampus, amygdala and temporal poles (Fig. 1; for detailed descriptions of Roger’s profile see1,2). All healthy comparison participants were screened for the presence of any neurological, psychiatric, cardiac or respiratory disease. None of the participants were smokers, and all participants demonstrated a normal 12 lead electrocardiogram (EKG), as assessed by a board certified cardiologist or neurologist.. Tasks Using a previously developed protocol3, participants rated the experience of heartbeat sensations following bolus intravenous infusions of isoproterenol (a beta adrenergic agonist similar to adrenaline) and saline. This protocol was adopted after preliminary testing with Roger on another heartbeat detection task4,5 (modeled after6) revealed chance heartbeat detection performance within the normal range (Roger’s average detection rate = 53%; 14 age–matched male healthy comparison’s average detection rate = 61%, SD 12%). After each bolus, participants turned a dial to track their ongoing, moment–to–moment experience of the overall intensity of heartbeat sensations. The dial could range from 0 (“normal, i.e., no change in intensity”) to 10 (“most ever”). The dial was always set to zero at the beginning of each infusion, and participants were specifically instructed to keep the dial at zero if they did not notice any increase in the intensity of heartbeat sensations above baseline levels. Drug administration was randomized and double blinded with the assistance of a skilled nurse. Participants were informed ahead of time that they would be receiving both isoproterenol and saline infusions at some point during the challenge, and were told what the isoproterenol sensations might feel like (e.g., “you may notice your heart beating harder and faster, and/or may feel an increase in your breathing sensations”). Each infusion period lasted approximately 2 minutes. At the onset of each infusion period participants were verbally notified (e.g., “infusion starting”). All infusions were delivered a minimum of 3.5 minutes apart. Since Roger has an anterograde memory impairment, his task instructions were repeated prior to each bolus. During extensive testing sessions in our laboratory, Roger has demonstrated an intact ability to follow experimental instructions over prolonged periods of time (on the order of several minutes and longer). The moment–to–moment nature of the dial rating protocol employed in the current study was designed to alleviate potential memory confounds associated with retrospective ratings7,8. Moreover, verbal reports during all infusion periods indicate that Roger understood the task instructions and was following them appropriately. All participants received two challenges of isoproterenol and saline infusions. During the first challenge, participants rated their experience of heartbeat sensations immediately following bolus infusions of isoproterenol and normal saline. During the second challenge, participants again rated their experience of heartbeat sensations following application of a topical lidocaine anesthetic to the body surface where the heartbeat sensation was felt maximally during the previous challenge (Fig. 3c), and participants once again rated their experience of heartbeat sensations. Infusion protocol The first challenge consisted of 14 infusions: 7 isoproterenol (0.1, 0.25, 0.5, 0.75, 1.0, 2.0 and 4.0 micrograms (mcg)) and 7 saline. These doses were used to establish the chronotropic dose 25 (CD25), which is the dose necessary to increase the participant’s heart rate by 25 beats per minute above baseline, a commonly reported measure of beta adrenergic receptor sensitivity9–13. The CD25 was calculated by extrapolation from the slope of a linear regression at each individual’s isoproterenol induced heart rate response9,12–14. The second challenge consisted of four infusions: 2 isoproterenol (2.0 and 4.0 mcg) and 2 saline. We only selected the two highest doses for the second challenge, as we have previously found that all participants receiving the 2.0 mcg dose experience report changes in heartbeat sensations3. Each infusion (isoproterenol and saline) consisted of two 3 milliliter (ml) bolus infusions delivered sequentially through an intravenous catheter. During isoproterenol infusions, a 3 ml bolus containing the specified dose was delivered, immediately followed by a 3 ml bolus of saline to flush the line. During saline infusions, a 3 ml bolus of saline was delivered, immediately followed by an additional 3 ml bolus of saline. Both bolus volumes were administered in entirety within a 15 second period by a nurse. This method of delivery minimized the participant’s ability to use external cues to distinguish between the different infusion types, and ensured rapid and standardized systemic introduction of isoproterenol. Anesthetic protocol Sixty grams of 4% lidocaine topical anesthetic cream (L.M.X.4TM, Ferndale Laboratories, Inc.) were applied to the body region where each participant reported maximally feeling their heartbeat sensations during the first infusion challenge (Fig. 3c). Anesthetic administration was single blinded. To ameliorate possible placebo effects, all participants were informed that the topical cream would either (a) increase skin sensitivity to heartbeat sensations, (b) decrease skin sensitivity to heartbeat sensations, or (c) would not change skin sensitivity to heartbeat sensations at all. In order to achieve an anesthetic effect the topical cream was left in place for a minimum of 30 minutes prior to the start of the second infusion challenge. To maintain adequate anesthesia, the anesthetic was left in place throughout the second infusion challenge. Anesthetic body surface area coverage was equivalent across all participants (Roger: 1.3%, healthy comparison participants: mean 1.7%, SD 0.7%)15. After the conclusion of the second infusion set, quantitative pinprick testing was conducted to determine whether an anesthetic effect had been obtained. Throughout the testing each participant was instructed to keep their eyes closed. A series of 18 stimulations were then applied to the participant’s body, 50% in the anesthetized area and 50% within a 10 cm radius of adjacent (non–anesthetized) skin. Participants were asked to spontaneously report whether they had experienced a sharp or dull sensation. A report of “dull” in the anesthetized area was considered correct, whereas a report of “sharp” in the same area was incorrect. The opposite criteria were applied to the adjacent non–anesthetized skin. Any participant achieving > 13 out of 18 trials correct or > 72% correct (p < .05 per binomial test) was considered to have demonstrated a satisfactory anesthetic effect. The quantitative sensory testing results showed that all participants demonstrated a satisfactory anesthetic effect according to this criterion (Roger: 83% correct, healthy comparison participants: mean 83% correct, SD 11%). Procedure The study involved one visit, which always started between 7 and 8am in the General Clinical Research Center at the University of Iowa. After completing the consent process a nurse measured each participant’s height and weight. The nurse then placed a 22 gauge intravenous catheter into the participant’s non dominant dorsal hand vein, and administered a 12 lead EKG. A physician evaluated the EKG, and the experiment proceeded only if the EKG was considered normal (all participants displayed normal EKGs). The participant was led to a quiet room, seated in a comfortable chair, and was attached to leads for measuring heart rate (lead II EKG). At this point the participant’s non dominant hand was placed outstretched on a pillow at chest level. A curtain was positioned with the participant on one side and the nurse and the experimenter on the other side, to prevent the participant from viewing the preparation and administration of each infusion. The nurse then measured the participant’s blood pressure and began the infusion protocol. Participants were instructed not to recline in the chair during each infusion period, in order to prevent them from using the back of the chair as an external source to help them detect heartbeat sensations. The entire procedure lasted approximately 5 hours. Psychophysiological measures Physiological data including heart rate were recorded continuously during all infusions with an MP100 acquisition unit (Biopac Systems, Inc). Dial ratings were collected with a custom built dial that consisted of a rotating potentiometer with a continuous range of 0.000 to 5.000 Volts. The average heart rate response during each infusion was calculated across a 120–second interval immediately following the onset of each infusion. The average heart rate response was obtained by subtracting the average heart rate during the 30–second post–infusion window (i.e., before isoproterenol–induced heart rate changes had occurred) from the average heart rate during the subsequent 90– second window (i.e., when the isoproterenol induced heart rate changes were most likely to occur). These time windows were carefully chosen to coincide with the typical delays observed in the onset of isoproterenol–induced heart rate changes (mainly due to the slow rate of venous drainage to the heart)9,11-14. All artifacts affecting the instantaneous heart rate waveform (e.g., movement related, or due to premature ventricular contractions) were manually identified and removed. Cross correlations for each participant were calculated in Matlab (Mathworks, Inc.) from mean centered dial ratings and instantaneous heart rate changes occurring over the 120–second interval following the onset of each infusion. Dial ratings and instantaneous heart rate changes for each dose were mean centered by subtracting the 120–second mean for each infusion interval from each time point within that interval. Supplementary Results See Supplementary Fig. 1a,b for full results of heart rate response and interoceptive awareness testing of all seven doses (0.1, 0.25, 0.5, 0.75, 1.0, 2.0 and 4.0 mcg) during the first challenge (i.e., without lidocaine anesthetic). All participants correctly detected increases in heartbeat sensations at the two highest doses (2.0 and 4.0 mcg), as indicated by a positive dial rating during the infusion period (Supplementary Fig. 1c). Roger correctly detected increases in heartbeat sensations at the four highest doses (0.75, 1.0, 2.0 and 4.0 mcg), as further indicated by his verbal responses (Supplementary Table 2). Cross correlation analysis of the time course of subjective and objective interoceptive changes revealed comparable zero order and maximum cross correlations between Roger and the comparison participants (Supplementary Fig. 1d). On average, Roger tended to generate ratings that were somewhat delayed with respect to the heart rate changes, with dose–dependent ratings that were similar in amplitude to the comparison participants. See Supplementary Fig. 2a,b for full results of heart rate response and interoceptive awareness testing of the two highest doses (2.0 and 4.0 mcg), following topical anesthetic application. Under this condition, Roger no longer detected any increase in heartbeat sensations, as indicated by the absence of dial ratings (Supplementary Fig. 2b,d,e), and as further indicated by his verbal responses (Supplementary Table 3). On the contrary, healthy comparison participants’ ratings were unaffected by anesthetic application, although it remains possible that there could have been subtle reductions in interoceptive awareness that were not picked up by our measurement. For example, anesthetic seemed to abolish sensation in one healthy comparison subject at the 2.0 mcg dose (91% of healthy participants reported a change in sensation), but this was not the case for the 4.0 mcg dose (100% of participants reported a change in sensation) (Supplementary Fig. 2d). Supplementary Table 1. Participant demographic data. Means +/– SD. Chronotropic dose 25 (CD25) is the isoproterenol dose necessary to increase the participant’s heart rate by 25 beats per minute above baseline. Age (yrs) Sex Body Mass Index CD25 (mcg) Roger 55 Male 29.4 8.1 Healthy comparison 54 +/– 9.6 11 Males 25.8 +/– 5.1 7.8 +/– 3.0 Supplementary Table 2. Verbal reports obtained during the non–anesthetized condition, 4.0 mcg dose. This particular healthy comparison participant used a numerical scale when verbalizing his sensation that went from 0 (“normal, i.e., no change in intensity”) to 10 (“most ever”). HR change refers to increase above baseline heart rate at the start of the infusion. Roger Comparison participant HR (bpm) 90 HR change 13 Verbal rating “Still pretty low” HR (bpm) 80 HR change 8 Verbal rating “3 maybe” 103 26 “It’s increasing some” 86 14 “4…a sense of fullness…from going up a couple flights of stairs” 91 14 78 6 “2…maybe 1” 87 10 “Not beating real hard or fast” “Now it’s closer to normal” 72 0 0 Supplementary Table 3. Verbal reports obtained during the anesthetized condition, 4.0 mcg dose. This particular healthy comparison participant used a numerical scale when verbalizing his sensation that went from 0 (“normal, i.e., no change in intensity”) to 10 (“most ever”). HR change refers to increase above baseline heart rate at the start of the infusion. Roger Comparison participant HR (bpm) HR change Verbal rating HR (bpm) HR change Verbal rating 94 10 “I haven’t noticed hardly any…any increase in heartbeat 85 2 “1” 107 23 “Not great heartbeat” 97 14 “2. Within my chest, It’s slightly faster, the beat has more power to it, akin to a quick walk or maybe a full flight of stairs” 109 25 “Pretty quiet, calm” 95 12 [Where in your body are you feeling it?] “In the chest under the gel area.” [Are you feeling it in your skin?] “No. Not in the skin, all within the chest cavity. It’s like a pulsing within” 105 21 [Would you describe it as normal?] “Yes” 80 –3 “0” 99 15 “I think it’s pretty normal” Supplementary Figure 1. Objective and subjective interoceptive changes during isoproterenol infusions. (a) Mean heart rate response to isoproterenol and saline. (b) Mean time course of heart rate response and subjective dial rating. Bolus infusions occurred at time zero. (c) Percent of participants correctly detecting increases in heartbeat intensity. A participant was considered to have correctly detected an increased heartbeat intensity if they turned the dial above zero at any point during the latter 90 seconds of the infusion period, when isoproterenol induced heart rate changes are most likely to occur. (d) Mean zero lag and maximum cross correlations between heart rate response and subjective interoceptive rating as a function of absolute lag time. Error bars = SE. Supplementary Figure 2. Objective and subjective interoceptive changes during isoproterenol infusions following topical anesthetic application. (a) Mean heart rate response to isoproterenol and saline. (b) Mean time course of heart rate response and subjective dial rating. (c) Overlaps showing area of topical anesthetic application, corresponding to the region of maximal heartbeat sensation. (d) Percent of participants correctly detecting increases in heartbeat intensity. (e) Mean zero lag and maximum cross correlations between heart rate response and subjective interoceptive rating as a function of absolute lag time. All comparison data depict mean values, except (c). Error bars = SE. References 1. 2. 3. 4. 5. 6. 7. 8. Tranel, D., Damasio, H., Damasio, A.R. in Handbook of Neuropsychology (eds. Boller, F., Grafman, J.) 85–110 (Elsevier science, Amsterdam, 2000). Feinstein, J. S. et al. Bilateral limbic system destruction in man. J Clinical Exper Neuropsych (in press). Khalsa, S. S., Rudrauf, D., Sandesara, C., Olshansky, B. & Tranel, D. Bolus isoproterenol infusions provide a reliable method for assessing interoceptive awareness. Int J Psychophys 72, 34–45 (2009) Khalsa, S., Rudrauf, D. & Tranel, D. Interoceptive awareness declines with age. Psychophysiology (in press). Khalsa, S. S. et al. Interoceptive awareness in experienced meditators. Psychophysiology 45, 671–77 (2008). Critchley, H. D., Wiens, S., Rotshtein, P., Ohman, A. & Dolan, R. J. Neural systems supporting interoceptive awareness. Nat Neurosci 7, 189–95 (2004). Craske, M. G., Tsao, J.C. Self-monitoring with panic and anxiety disorders. Psychol Assessment 11, 466–479. (1999). Hutcherson, C. A. et al. Attention and emotion: does rating emotion alter neural responses to amusing and sad films? Neuroimage 27, 656–68 (2005). 9. 10. 11. 12. 13. 14. 15. Cleaveland, C. R., Rangno, R. E. & Shand, D. G. A standardized isoproterenol sensitivity test. The effects of sinus arrhythmia, atropine, and propranolol. Arch Intern Med 130, 47–52 (1972). Martinsson, A., Lindvall, K., Melcher, A. & Hjemdahl, P. Beta-adrenergic receptor responsiveness to isoprenaline in humans: concentration-effect, as compared with dose-effect evaluation and influence of autonomic reflexes. Br J Clin Pharmacol 28, 83–94 (1989). Contrada, R. J., Dimsdale, J., Levy, L. & Weiss, T. Effects of isoproterenol on Twave amplitude and heart rate: a dose-response study. Psychophysiology 28, 458– 62 (1991). Mills, P. J., Dimsdale, J. E., Ancoli-Israel, S., Clausen, J. & Loredo, J. S. The effects of hypoxia and sleep apnea on isoproterenol sensitivity. Sleep 21, 731–5 (1998). Yu, B. H., Kang, E. H., Ziegler, M. G., Mills, P. J. & Dimsdale, J. E. Mood states, sympathetic activity, and in vivo beta-adrenergic receptor function in a normal population. Depress Anxiety 25 559–64 (2007). Arnold, J. M. & McDevitt, D. G. Standardised isoprenaline sensitivity tests--a comparison of existent methods. Br J Clin Pharmacol 15, 167–72 (1983). Mosteller, R. D. Simplified calculation of body surface area. N Engl J Med 317, 1098 (1987).