The skin conductance response, also known as the electrodermal response (and in older terminology as "galvanic skin response"), is the phenomenon that the. Electrodermal activity (EDA) is the property of the human body that causes continuous variation in the electrical characteristics of the skin. Historically, EDA has also been known as skin conductance, galvanic skin. Skin conductance (SC) is normally measured with 8mm diameter silver/silver chloride electrodes positioned on the medial phalanx of the index and middle.
During this phase the colored circles will be presented again, and some of them will be followed by the electric stimulus. Again, you should sit quietly and look at each colored circle as it is presented. During this phase you will see more colored circles.
However, you will no longer receive any electric stimulation. Please continue to sit quietly and look at each colored circle as it is presented. It is important that you watch the screen at all times.
Do you have any questions? After the subject indicated readiness to proceed, the technician activated the computer, which took over administration of the experiment. After a 5-min resting period, the three phases of the experiment were initiated. During each phase, the CS duration was 8 s, and the intertrial intervals ITIs ranged from 15—25 s, with the duration of each ITI determined at random by the computer. Skin conductance response scores were analyzed in two ways: Scoring criteria for FIR and SIR were guided by our reading of the older literature, our presumptions about scoring decisions made by previous investigators that were not explicitly elaborated in the published reports, and practical considerations from inspection of the present data.
Below, we have tried to provide a concise, but clear, description of the method arrived at for scoring the FIR and SIR. However, we suffer no delusion that this is the final answer and that some readers will not argue with one or more of our interpretations and assumptions. A copy of the Mathematica-based scoring algorithm and program we developed is available on request; use of this program requires access to Mathematica 6 Wolfram Research Inc.
This scoring algorithm identifies response onset for the FIR and SIR by finding the point of maximum curvature of the SCL data within a pre-specified onset window and then stepping forward or backward until the slope changes from negative to positive or positive to negative.
This point of slope change defines the response onset. A response peak is found by locating the highest SC value after the identified onset and within the window specified for the peak. In order for a response to be scored, neither its onset nor peak can be located at the first or last data point in their respective window.
If this occurs, the window is shrunk and the algorithm looks for a new onset or peak. An exception to this is when the data are flat in the vicinity of an onset that occurs at the first data point, in which case the requirement is that the data remain flat for 0. The search for an onset or peak continues until the lowest onset SCL value and highest peak SCL value are identified in their respective windows, or a window reaches zero width.
A zero-width window indicates that an onset or peak cannot be found and no response for the interval is calculated.
If the value of the last data point within the SIR window exceeded the identified peak, that value was substituted for the SIR peak value. For the present study, the mathematical expression used to characterize curvature of the SC data was closely approximated by the second derivative, because the first derivative was found to be much less than one.
As determined from the extant literature, windows for potentially locating a response onset and peak were specified as follows for the FIR and SIR. For the FIR, we required that the inflection point of a response onset occur within 1—4 s, and that the response peak occur within 2—6 s, following CS onset. For the SIR, we required that the inflection point of response onset occur within 4—8 s, and that the response peak occur within 5—9. Skin conductance data were not collected during the actual UCS presentation i.
Consequently, the SIR peak could be slightly underestimated if it occurred within the 0. The SIR window, even though it extends to 9. When the FIRs and SIRs were averaged over trials, zero entries were used for trials that produced no identifiable response. A square-root transformation was applied to all response scores. Each line denotes the average SC levels over time for each of the 10 trials. In addition, 18 participants did not exhibit a SIR on any acquisition trial and four participants did not exhibit a FIR on any acquisition trial, but did exhibit a SIR on at least one of these trials.
For the FIR, mean onset latency ranged from 1. For the SIR, mean onset latency ranged from 6. Analyses of variance ANOVA for repeated measures were conducted separately for the three phases of the procedure: See Table 3 and Figure 2 for a summary of these results. All significance levels reported for analyses that included the Trials variable reflect the Greenhouse-Geisser correction; however, the original degrees of freedom are presented when reporting the statistical tests.
All significance levels reported for analyses that included the Trials effect reflect the Greenhouse-Geisser correction for violation of the sphericity assumption.
However, in order to minimize possible confusion arising from different degrees of freedom being reported for similar analyses, we report the degrees of freedom associated with the unadjusted tests.
Skin conductance response magnitude showed an overall decrease over trials. The repeated-measures ANOVA for the EIR produced a significant Trials main effect, which appeared to have a repeated pattern of increases and decreases over the course of the trials.
Another set of analyses focused on testing individual differences between those who responded more strongly at the beginning of the CS-UCS interval FIR and those who responded more strongly towards the end SIR. Based on these data, participants were divided into two groups: Comparisons of these groups indicated that they did not differ on measures of psychological distress Derogatis, , depression Beck et al.
Based on our comprehensive review of the differential aversive conditioning literature and the cumulative findings from these studies, differential conditioned responses appear to be observable in both the FIR and SIR. In addition to this review, we addressed the utility of separately scoring the FIR and SIR through a secondary analysis of SC data obtained from a differential aversive conditioning procedure administered in the context of a large study of police and firefighter trainees.
The primary outcome of the secondary analyses is clearly evident in Figure 1 , where it can be seen that the SC responses to the 8-s duration conditioned stimuli are primarily characterized by a single, prominent peak that occurs around 3—4 s following CS onset. It is worth noting that the latency of this peak remained remarkably stable across trials. As can be seen in the figure, there is almost no displacement of this peak from early to late trials.
However, a longer CS-UCS interval than that used in the present study, or more conditioning trials, may be necessary to reveal a progressive shift in the response peak, if one exists. Although Figure 1 suggests a single SC response peak, statistical analyses indicate that effect of differential conditioning can be detected in the SIR, as well as the FIR. It is possible that the absence of a more distinctive SIR peak in the figures is due, at least in part, to greater variability in the SIR peak latency, i.
This is further reflected in the effect sizes for differential conditioning, which were comparable for the three measures. These results support the use of either the FIR or EIR to detect differential aversive conditioning effects and suggest that there is no substantive difference between the scores generated by the method used to calculate the EIR and that used to calculate the FIR. Both scoring methods seem capable of adequately representing conditioned SC responses generated by a differential aversive conditioning procedure that uses a long CS-UCS interval.
However, from an individual-differences perspective, individuals who show relatively larger FIRs, compared to those who show relatively larger SIRs, do not appear to differ on measures commonly thought to influence differential conditioning e. The lack of meaningful psychological differences between individuals who preferentially exhibit a FIR or SIR suggests that separate measurement of these two responses may be unnecessary.
This eliminates the risk of underestimating a larger CR when the onset or peak of the response occurs near a previously established boundary between the FIR and SIR or when the latency of the peak response shifts over trials. Second, from a practical standpoint, the method used to calculate the EIR reflects a much simpler way of scoring data. This method, as applied in the present study, simply calculates a pre-stimulus-onset SC level by averaging data over a brief duration we used 2 s , identifies the highest SC level i.
Because SC responses have relatively long onset latencies, it would also be reasonable to use the SC level immediately following stimulus onset e.
Scoring is easily accomplished within one of the currently available spreadsheets e. Most importantly, this method does not require undertaking the complex process of mathematically modeling SC data curves, identifying points of inflection that define a response onset and creating, or learning to use, software that can accomplish this process.
Although there appear to be advantages to using the EIR rather than the FIR and SIR, it is important to note some potential limitations to the generalizability of our findings.
First, because there were only five acquisition trial pairs, we are unable to assess whether similar results would be observed for longer acquisition phases that included a greater number of trials. Similarly, because the CR extinguished very quickly for most participants, likely due to the extinction instructions, we were unable to assess the utility of the EIR vs. Finally, because this dataset is derived from one study, it is possible that specific aspects of the procedures may have contributed to the results.
In sum, based on the existing electrodermal conditioning literature and secondary data analysis, it appears that separating SC responses into FIR and SIR components in differential aversive conditioning studies may not be warranted.
Instead, use of the EIR to capture the SC response is recommended, at least in studies that administer relatively few acquisition trials. This research was supported by U. We would also like to express our appreciation to the police and firefighters for their willingness to participate. National Center for Biotechnology Information , U.
Author manuscript; available in PMC May Pineles , a, b Matthew R. Orr , c and Scott P. Author information Copyright and License information Disclaimer. Address reprint requests to: The publisher's final edited version of this article is available at Psychophysiology. See other articles in PMC that cite the published article. Abstract Researchers examining skin conductance SC as a measure of aversive conditioning commonly separate the SC response into two components when the CS-UCS interval is sufficiently long.
Conditioning, Electrodermal response skin electric response , Scoring methods. Ext Interval 1 Interaction? Ext Interval 2 Main effect? Ext Interval 2 Interaction? Open in a separate window. Method Participants Police and firefighter trainees were recruited from the: Procedure The experimental session took place in a humidity- and temperature-controlled room located in quiet areas of the respective training academies.
Once the UCS level was established, the subject was given the following instructions: Response Scoring Skin conductance response scores were analyzed in two ways: Acknowledgments This research was supported by U.
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During the task, the monkeys fixated for ms on a square fixation icon subtending 0. Successful image viewing 3 s was rewarded with 1 mL liquid reward. If the monkey failed to maintain gaze on the image, the image was removed, and a 2-s period was added to the 3-s intertrial interval. The stimuli depicted social monkeys, humans, other animals and nonsocial objects, fractals, landscapes factors. Monkey faces were chosen from a large library which categorized the images along the dimensions of monkey identity, direction of gaze averted or direct , and facial expression appeasing, neutral, or threatening Gothard et al.
A stimulus set consisted of 10—24 images, presented in pseudorandom succession within 10—30 repeated trial blocks. Each monkey was seated in a dimly lit room and allowed to drift in and out of sleep. The duration of this time period was not fixed, but a typical session would last 30 min. Two states within the rest condition were also identified: The onset of SCRs was detected using a custom-designed Matlab script to identify positive deflections in the first derivative of smoothed electrodermal activity ms moving average.
SCRs were user verified in accordance with the canonical waveform described by Edelberg SCRs occurring 1—3 s after image onset were attributed to the image on the basis that the minimum latency of an SCR that could be elicited by an unexpected loud tone was 1.
During the image viewing task, the probability of an SCR occurring at each of 30 time bins of ms each, spanning the time course of trial events, was calculated for both monkeys. Spearman's rank correlation was used to determine if either the probability of images eliciting SCRs within a block or the magnitude of evoked SCRs indicated habituation of either measure. Within the rest period, perievent time histograms of SCR occurrences were constructed using 1-s time bins spanning a s window centered at the opening and closing of the eyes.
The raw spike trains were converted to continuous firing rates using the spike count observed in a 1-s moving window translated across the spike train with a 1-ms step size. SCR-triggered averages were computed for each unit within a s time window centered at the onset of SCRs.
Each SCR-triggered average was normalized to its own baseline activity by subtracting the mean of the entire trace from the value of each time point along the trace. Additionally, for each individual SCR-triggered firing rate average, the largest deviation from baseline that occurred in the 2 s period prior to SCR onset expressed as a z-score was computed.
The mean and median change in firing rate was calculated at each time point across the population of mean-corrected SCR-triggered averages. The resulting population trace was then expressed in units of SDs away from its own mean z -score. This was computed to determine if the net change from baseline firing activity observed across the population was significantly different near the onset of SCRs than at any other time. The procedure was also carried out after mean-corrected SCR-triggered averages had been converted to absolute values, as this would allow evaluation based only on the absolute magnitude of deviation from baseline.
Finally, the raw spike train of each unit was used to create a peri-SCR time histogram with ms bins spanning a s window. The locations of the significant bins were then recorded for each unit and combined into summary histograms Fig. Neural activity centered on SCR onset in different experimental conditions.
SCR-triggered firing rate averages were calculated for each unit and normalized to their baseline firing rates.
At each time point, the population mean black trace and median gray trace were calculated. This convention is carried over into C. The horizontal dotted lines indicate a z -score value of 3. The traces in C were calculated as in B except that each normalized SCR-triggered average was first converted to changes in the absolute value of the firing rate.
When only response magnitude is considered A and C , clear SCR-related activity is evident in both experimental conditions. The effects are cancelled out when direction is considered as well B. Monkey T viewed 14 image sets 3, image presentations , and monkey H viewed 9 image sets 1, image presentations.
Figure 2 A shows the probability of SCR occurrence in both monkeys as a function of trial progress. Because the minimum latency for an SCR is 1 s, the SCRs produced by monkey T can be attributed to the images or anticipation of reward, whereas in monkey H , the SCRs were triggered by anticipation of stimulus images or reward delivery from the previous trial.
Probability of SCR occurrence across all sessions as a function of trial progress during the image viewing task. Histograms of SCR occurrence in monkeys H and T top and bottom , respectively centered on the closing and opening of the eyes.
The average time spent in each rest session with eyes open and closed were The change in SCR frequency between the two states was time locked to the opening and closing of the eyes Fig. During the period of rest, single units were recorded from the amygdala 48 from monkey H , 56 from monkey T and during image viewing, a different set of single units were recorded and 47 units from monkeys H and T , respectively.
The number of single units recorded from each nucleus and their respective average firing rates are presented in Supplementary Table S2. More units exhibited significant modulations in neural activity during the 2 s preceding SCR onset than any other time over the course of a s time window Fig. Each ms time bin in Fig. At the population level, no clear net increase or decrease of firing rate was observed surrounding the onset of SCRs Fig.
This might reflect the cancellation of responses that occurred in positive and negative directions with regard to baseline activity e. When only the magnitude of deviation from baseline activity is considered, a significant increase in the population's mean and median deviation from baseline emerges during the 2 s before SCR onset Fig.
The response distribution across the population of single units was bimodal and approximately symmetric Fig. Recordings from the basolateral lateral, basal, and accessory basal nuclei and centromedial central and medial nucleus, as well as the anterior amygdaloid area nuclei had similar response distributions within both conditions image viewing: Distribution of SCR-related firing rate modulations across the population of single units for both experimental conditions.
Single units are evenly split between those that show positive and negative changes in firing rate. The magnitudes of these responses are comparable, suggesting 2 distinct populations of units. During the rest period, the probability of SCR occurrence was modulated by the opening and closing of the eyes Fig.
When SCRs that occurred within 10 s of the eyes opening or closing were removed from the analysis, SCR-related activity was still clearly present Fig. SCR-related neural activity is not dominated by the opening and closing of the eyes. Although this technique had the effect of decreasing the number of highly modulated units compare A with Fig.
The results presented here indicate that neural activity in the amygdala marks the occurrence of an SCR regardless of its immediate trigger. In the context of a passive image viewing task, SCRs can occur spontaneously or be triggered by task-related factors.
Given the variety of causative factors, the occurrence of an SCR cannot be used as an independent and reliable measure of stimulus image content, at least under these experimental conditions. Even so, the amplitudes of image-evoked SCRs do seem to be useful in determining which categories of images are on average more arousing.
Within the rest condition, a fraction of the observed SCRs were related to the opening of the eyes, yet SCR-related activity was independent of this trigger, and the remaining SCRs could not be attributed to any tractable event. SCR-related changes in firing rate had a bimodal distribution regardless of the nucleus from which each unit was recorded.
A similar bimodal distribution of response types was reported by Pascoe and Kapp in the central nucleus of the rabbit amygdala in conjunction with conditioned heart rate deceleration. The presence of neurons that either increase or decrease their firing rates in relation to the same autonomic output suggest that multiple pathways transmit signals from the amygdala to the autonomic centers of the brain stem.
The SCR-related activity observed in various nuclei of the amygdala may have different functional consequences. The centromedial nuclei are reciprocally connected to the autonomic centers of the brain stem and hypothalamus Price and Amaral and could directly influence the generation of SCRs.
The basolateral nuclei are not connected to autonomic effectors; rather, they send excitatory feedback connections to multiple cortical areas that process incoming sensory information Amaral and Price The SCR-related activity observed in this nuclear group might reflect the recruitment of attentional resources, which may itself elicit autonomic arousal Critchley Although we did not find differential patterns of activity between the basolateral and centromedial groups, it is possible that such a difference would emerge in relation to associative or instrumental learning.
These effects are most likely reflected in increased BOLD signals in the amygdala e. Importantly, our data show that SCR-related activity within the amygdala need not be elicited exclusively by strong emotion, fear conditioning, or sudden changes in the external environment.
Previous studies indicate that the monkey amygdala is differentially activated by images both at the single-unit and population level Gothard et al. In humans, functional imaging studies also show the amygdala to respond differentially to certain image types, often along emotional lines Liberzon et al. Emotion, however, may not be the only factor involved. Images of monkeys with averted gaze elicited larger SCRs than the same monkeys with gaze directed at the viewer, regardless of facial expression.
A similar case has been made to explain the increased BOLD signals in the amygdala of monkeys viewing indirect versus direct gaze faces Hoffman et al. Regardless of the specific triggers of autonomic arousal, the overall SCR-related activity in the amygdala was found to be similar across different behavioral states. Our findings, therefore support the view that in addition to stimulus-specific responses, the amygdala may play a broader role in the modulation of sympathetic tone.
Finally, the amygdala is only one of many structures involved with emotion, attention, and autonomic regulation. The medial and orbital prefrontal cortices, the anterior insula, the anterior cingulate cortex, and periaquaductal gray have overlapping roles in the evaluation of emotional stimuli and in the initiation of autonomic responses, including SCRs Critchley Further studies will be required to understand fully what unique role the amygdala plays in the generation and modulation of SCRs under various conditions.
Our data indicate that the amygdala participates in the generation of sympathetic arousal in response to multiple triggers and even in the absence of explicit stimuli. Zimmerman was responsible for anesthesia, postoperative care, and behavioral training of monkeys involved in this project. Zimmerman for help with data collection. Gibboni III helped with data analysis. We are grateful to Dr. Bruce McNaughton, who edited the final versions of the manuscript.
The costs of publication of this article were defrayed in part by the payment of page charges. Section solely to indicate this fact. National Center for Biotechnology Information , U. Published online Jan Laine , Kevin M. Spitler , Clayton P. Mosher , and Katalin M.
Jul 17, Skin conductance is not under conscious control. Instead, it is modulated autonomously by sympathetic activity which drives aspects of human. Skin conductance (SC) has a simple curve form always with an initial rapid increase and a slower recovery. SP curves are more complicated. Many papers, such. The skin conductance response (SCR) is an indirect measure of sympathetic autonomic activity that is associated with both emotion and attention. In humans.