Conceived and designed the experiments: ZK JS. Performed the experiments: ZK. Analyzed the data: QY. Contributed reagents/materials/analysis tools: QY. Wrote the paper: ZK QY AB PB.
The authors have declared that no competing interests exist.
This study aimed to objectivize the quality of smooth pursuit eye movements in a standard laboratory task before and after an Eye Movement Desensitization and Reprocessing (EMDR) session run on seven healthy volunteers. EMDR was applied on autobiographic worries causing moderate distress. The EMDR session was complete in 5 out of the 7 cases; distress measured by SUDS (Subjective Units of Discomfort Scale) decreased to a near zero value. Smooth pursuit eye movements were recorded by an Eyelink II video system before and after EMDR. For the five complete sessions, pursuit eye movement improved after their EMDR session. Notably, the number of saccade intrusions—catch-up saccades (CUS)—decreased and, reciprocally, there was an increase in the smooth components of the pursuit. Such an increase in the smoothness of the pursuit presumably reflects an improvement in the use of visual attention needed to follow the target accurately. Perhaps EMDR reduces distress thereby activating a cholinergic effect known to improve ocular pursuit.
Eye Movement Desensitization and Reprocessing (EMDR) is a therapy which is intended to treat anxiety, stress and trauma. It was developed by Francine Shapiro
EMDR stimulated various lines of research including laboratory research on the mechanisms involved and on the physiological correlates of EMDR. In what follows we will briefly review some of these studies.
Van den Hout et al.
Lee & Drummond
However, the objectives of the present study are perhaps more congruous with studies centered squarely on the various physiologic correlates of EMDR. Barrowcliff et al.
Barrowcliff et al.
More recently, Elofsson et al.
Several brain imaging studies have also been conducted to assess modifications in cerebral activity following EMDR treatment, some of them are briefly presented below. Levin et al.
To summarize, research on mechanisms and physiological correlates of the EMDR indicates the importance of eye movements in EMDR treatment. The controversy over the mechanisms behind the workings of EMDR, is one of the main issues of ongoing research. Yet, it may well be that the above mentioned hypotheses are equally true given that EMDR treatment is
The motivation of the present study comes also from clinical observation of changes in smoothness of pursuit eye movements during EMDR session. We hypothesize that lack of smoothness of pursuit eye movements reflects stress and emotional perturbation, and that reduction of the above by EMDR will increase such smoothness. In other words, we expect a similar effect as that shown in physiological studies, e.g. effects of nicotine on pursuit in schizophrenia. These studies will be reviewed below after a brief presentation of physiological aspects of pursuit eye movements.
Pursuit eye movement is the ability of the eyes to smoothly follow a small object moving in a stable environment as mentioned. The stimulus for the initiation of smooth pursuit is the velocity of the moving object, i.e. the slippage of the image away from the fovea. Processing of visual motion is primarily generated in the medial temporal lobe (area V5, e.g.
Pursuit may not be perfect even in healthy subjects. Several types of deficits may exist: slow initiation, low gain associated with saccade intrusions, or predictive saccades. Here we will be interested mainly in one type of small saccades appearing during smooth pursuit (SP), i.e. catch-up saccades (CUS). Catch-up saccades occur when the eyes are lagging behind with lower velocity than that of the moving target. Although the mechanisms that control both CUS and SP are still poorly understood, common structures seem to be involved in their control. For example, error signals on motion or position of the moving target in the superior colliculus (SC) could be shared by the saccadic and smooth system
Several studies reported pursuit deficits in psychological disorders such as
Sherr et al.
Patients with autism also show low pursuit gain for its initial period of 100 ms, but these deficits were only seen when targets moved from the center into the right visual field
This review although not exhaustive indicates abnormalities of pursuit eye movements in several disorders. Whether abnormalities of pursuit can be a biological marker of psychological disorders is a controversial issue
The goal of the present study was to objectivize in healthy volunteers the effects of an EMDR session on the physiology of pursuit eye movements studied in a laboratory setup. Pursuit eye movements were measured with video-oculography before and after an EMDR session carried out with persons evoking emotive memories. The frequency of CUS and the gain of smooth components during pursuit were analyzed. The results show decrease of frequency of CUS and increase of gain of smooth components after EMDR but only when the session was complete and distress dropped to zero.
The eye movement investigation adhered to the tenets of the Declaration of Helsinki and was approved by the local human experimentation committee, CPP Il de France II (No: 07035), Hospital Necker in Paris. Consent was obtained from all subjects after the nature of the procedure had been explained.
Seven healthy subjects (female, 32.2±8.5 years, mean ± standard deviation) participated in the study. Three of them were students in the psychology university and the others were psychotherapists; all of them had intellectual interest for the EMDR relative to their professional projects. They were questioned on known physical, psychiatric illness, medications, prior or current followed up by psychotherapist; ophthalmologic problems and pregnancy were also excluded. All subjects were healthy, well functioning with stable everyday life. Moreover, they were invited to choose an autobiographic negative event of moderate distress; this was evaluated afterwards following the EMDR protocol (see below). General information about EMDR was given as required by the EMDR protocol. Information about the pursuit physiologic eye movement test was also given: presentation of the task, of the viseo-oculography apparatus, and of the purpose of the test - understanding the neuro-physiology of pursuit eye movement control in humans. To avoid bias, the specific hypothesis of the study, i.e. possible influence of the EMDR on parameters of pursuit eye movements, was not communicated to the subjects. The EMDR therapy was done by a therapist who had received a training (level 2) accredited by the French EMDR association.
EMDR protocol involves evaluation of distress intensity. In this study, the Subjective Units of Discomfort Scale was used
Age (Year) | Gender | SUDs Before | After | VOC Before | After | |
S1 | 22 | F | 6 | 0 | 3 | |
S2 | 24 | F | 6 | 2.5 | 2 | |
S3 | 30 | F | 8 | 3 | 1 | |
S4 | 42 | F | 4 | 0 | 2 | |
S5 | 38 | F | 6 | 0 | 4 | |
S6 | 38 | F | 7 | 0 | 2 | |
S7 | 38 | F | 8 | 0 | 3 | |
Mean (SD) | 33(7.8) | 6.4 (1.4) | 0.8 (1.4) | 2.4 (1.0) | 7 (0) |
The stimulus consisted of a black dot (0.2°) in the center of a grey background on the PC screen (
(A) Spatial arrangement for smooth pursuit: one white dot on the black computer screen, 57 cm from subject's eyes, moving from center to right or left (15°), randomly. (b) Temporal arrangement: the white dot moves to opposite direction to the pursuit then returns to center (200 ms) to begin pursuit, the stimulus at velocity of 15°/s. (c) Typical recording of normal rightward pursuit is obtained by averaging the position signal of the two eyes (LE+RE)/2; CUS indicates catch-up saccades during the pursuit.
As the goal of the study was to test for lasting physiologic effects after the EMDR on pursuit eye movement no instruction was given to connect with the target event worked during the EMDR session.
The Eyelink II video eye tracker was used; it consisted of infra-red cameras (CMOS sensors). The sampling frequency was 250 Hz.
Eye movement signals were calibrated using a linear function with factors extracted from the calibration task. We measured the gain of pursuit, e.g. ratio of mean velocity of pursuit phase (without saccades) to the stimulus velocity; the number of catch-up saccades (CUS, see
The Wilcoxon signed rank test (software Statistica) was used for group comparisons before and after EMDR measurements.
Individual traces of rightward smooth pursuit eye movements before and after EMDR for each subject. Each trace shows the instantaneous eye position over time during an individual trial. The thick diagonal line shows target displacement from centre the right of the screen. The eye movement starts after a latency period (see thick horizontal segment, s4). The eye position lagging behind target position frequently small catch up saccades are made (upward arrows). Occasionally the eye anticipates, e.g. going beyond target position and then a small saccade returns it back on the target (see downward arrow). The values of SUD and VOC are shown in cells of each figure. After EMDR all subjects show decrease of SUD and increase of VOC (when measured).
Individual traces of leftward smooth pursuit eye movements before and after EMDR for each subject. Each trace shows the instantaneous eye position over time during an individual trial. The thick diagonal line shows target displacement from centre to the left of the screen. The eye movement starts after a latency period (thick horizontal segment, s2). The eye position lagging behind target position frequently small catch up saccades are made (downward arrows). Occasionally the eye anticipates, going beyond target position and returns back (see upward arrow). All other notations as in
Individual mean values with their standard deviation of number of CUS (A), amplitude of CUS (B) and gain of pursuit (C); data are shown before and after EMDR for smooth pursuit to right. Group mean values are presented on the right of each group. Asterisks show statistically significant difference.
Individual mean values with their standard deviation of number of CUS (A), amplitude of CUS (B) and gain of pursuit (C); data are shown before and after EMDR for smooth pursuit to left. All other notations as in
The question arises whether the amount of CUS prior to EMDR session was within the normal range for these subjects. We extracted normal values from the literature, e.g. Friedman et al.
For other types of saccade intrusions, such as anticipatory saccade or square wave jerks (SWJ, see
The study aimed to objectivize the quality of smooth pursuit eye movements in a standard laboratory task before and after EMDR session. The EMDR session was applied on healthy subjects and on autobiographic worries causing moderate distress. The EMDR session was complete in 5 out of the 7 cases, and distress measured by SUD decreased to near zero value. Pursuit eye movements improved after the EMDR session, namely the number of CUS decreased and reciprocally, the gain of the smooth components of the pursuit increased. So the overall effect of EMDR was an improvement of the smoothness of the pursuit, i.e. as the eyes were lagging less behind the target there was less need for CUS. Such improvement presumably reflects better employment of visual attention resources needed to follow the moving target. Indeed prior studies have shown that the rate of CUS can increase in dual tasks in which subjects have to follow the pursuit target while listening to a voice pronouncing a letter series
One could also argue that the improvement is due to practice. To our knowledge, there is no evidence for decrease of rates of CUS just by practice. Analysis of our data over time, e.g. comparison between the first and last pursuit trial in a given session does not show a trend for such reduction. Note also that the time interval between before and after EMDR eye movement recording was about 90 min. A fatigue effect would cause increased rates of CUS but this was not the case. Rather, we suggest that improvements of pursuit could be related to modifications of cerebral activity due to decrease of distress after the EMDR session. This is in line with other studies; for instance with the study of Tregellas et al.
Perhaps EMDR reducing distress activates a cholinergic effect improving pursuit eye movements as does nicotine in schizophrenia
In conclusion it should be emphasized that the effects of pursuit improvement reported here are present after the EMDR session, and while the subject is in a laboratory setup. This suggests lasting beneficial effects. Eye movement semiology is known to be a great tool for exploring brain function and plasticity
The authors thank the association of EMDR France, David Servan-Schreiber's team, particularly Martine Iracane and Patrick Zillharalt supervising the investigator's EMDR training.