Abstract
Background
Complex Regional Pain Syndrome (CRPS) is a chronic and disabling condition in which pain, swelling and other symptoms arise in one or more limb(s). CRPS patients report slowed movements and a sense of detachment from their affected body-part(s). Patients are also slower to process tactile stimuli on whichever hand is positioned on the affected side of space. These symptoms have been likened to the syndrome of Hemispatial Neglect (“neglect”), which results from brain injury and is marked by decreased attention to the contralesional side of the body and space. Understanding the full nature of the spatial attention bias in CRPS patients and the extent to which it resembles neglect following brain injury could provide additional insights into the cortical underpinnings of CRPS and inform new treatments.
The current study examined the distribution of visual attention in patients with CRPS of the upper or lower limb for the first time.
Aims
We aimed to test visual attention in patients with CRPS. We hypothesised that they would attend less to targets appearing on the affected as compared to the unaffected side of space. Furthermore, we hypothesised that patients would show less precision in their judgements of spatial targets as compared to controls.
Methods
Twelve upper and 12 lower limb CRPS patients and 24 controls completed visual temporal order judgement (TOJ) tasks. Two lights were projected onto a table 9cm to the left and right of a fixation point and at offsets of 120, 60, 30, 15, 5, 5, 15, 30, 60 and 120 ms [negative numbers = light appeared on the affected (patients) / non-dominant (controls) side]. Participants stated which light appeared first. They completed the task three times: 1) with their hands out of sight (“no hands”), 2) with the left and right lights projecting onto the left and right hand, respectively (“hands uncrossed”), and 3) with the left and right lights projecting onto the right and left hand, respectively (“hands crossed”). Points of subjective simultaneity (PSSs) and just noticeable differences (JNDs) were obtained from psychometric functions fitted to individual data, and were analysed using bootstrapped linear mixed models regression (1000 samples).
Results
Group (patients or controls) was a predictor of PSS (β=22, 95%CI=[-44,-4]) and JND (β=24, 95%CI=[5, 41]). For patients, the light on the affected side of space had to appear, on average, 15ms earlier than the light on the unaffected side for the two to be perceived as simultaneous (95%CI=[-27,-2]). Controls exhibited no lateralized bias (PSS=-6, 95% CI=[-16, 6]). Overall, the JNDs of patients (M=96, 95%CI=[76, 117]) were 22ms larger than those of the controls (M=74, 95%CI=[54, 95]).
The patients’ biases were statistically similar in the no hands (PSS=-27, 95%CI=[-45, -8]) and the hands uncrossed conditions (PSS=-15, 95%CI=[ 30,6]), but significantly smaller in the hands crossed condition (PSS=-1, 95%CI=[-17, 15]). The difference between JNDs for controls and patients was comparable between the three hand arrangement conditions.
Limb (upper or lower) and side (left or right) did not contribute to the prediction of patient’s PSS or JND scores, but other clinical measures did.
Conclusion
The results provide the first empirical evidence for visual neglect in CRPS. This bias is not limited to visual information about the body because the PSS bias was largest for lights appearing on the table and did not differ between patients with upper and lower limb CRPS. The absence of a bias in the hands crossed condition may reflect an interaction of different spatial reference frames (i.e., attention to the body versus egocentric space) as has been demonstrated in stroke patients.
Larger JNDs in patients indicate decreased certainty when judging the order of visual targets, consistent with impaired body representation.
Complex Regional Pain Syndrome (CRPS) is a chronic and disabling condition in which pain, swelling and other symptoms arise in one or more limb(s). CRPS patients report slowed movements and a sense of detachment from their affected body-part(s). Patients are also slower to process tactile stimuli on whichever hand is positioned on the affected side of space. These symptoms have been likened to the syndrome of Hemispatial Neglect (“neglect”), which results from brain injury and is marked by decreased attention to the contralesional side of the body and space. Understanding the full nature of the spatial attention bias in CRPS patients and the extent to which it resembles neglect following brain injury could provide additional insights into the cortical underpinnings of CRPS and inform new treatments.
The current study examined the distribution of visual attention in patients with CRPS of the upper or lower limb for the first time.
Aims
We aimed to test visual attention in patients with CRPS. We hypothesised that they would attend less to targets appearing on the affected as compared to the unaffected side of space. Furthermore, we hypothesised that patients would show less precision in their judgements of spatial targets as compared to controls.
Methods
Twelve upper and 12 lower limb CRPS patients and 24 controls completed visual temporal order judgement (TOJ) tasks. Two lights were projected onto a table 9cm to the left and right of a fixation point and at offsets of 120, 60, 30, 15, 5, 5, 15, 30, 60 and 120 ms [negative numbers = light appeared on the affected (patients) / non-dominant (controls) side]. Participants stated which light appeared first. They completed the task three times: 1) with their hands out of sight (“no hands”), 2) with the left and right lights projecting onto the left and right hand, respectively (“hands uncrossed”), and 3) with the left and right lights projecting onto the right and left hand, respectively (“hands crossed”). Points of subjective simultaneity (PSSs) and just noticeable differences (JNDs) were obtained from psychometric functions fitted to individual data, and were analysed using bootstrapped linear mixed models regression (1000 samples).
Results
Group (patients or controls) was a predictor of PSS (β=22, 95%CI=[-44,-4]) and JND (β=24, 95%CI=[5, 41]). For patients, the light on the affected side of space had to appear, on average, 15ms earlier than the light on the unaffected side for the two to be perceived as simultaneous (95%CI=[-27,-2]). Controls exhibited no lateralized bias (PSS=-6, 95% CI=[-16, 6]). Overall, the JNDs of patients (M=96, 95%CI=[76, 117]) were 22ms larger than those of the controls (M=74, 95%CI=[54, 95]).
The patients’ biases were statistically similar in the no hands (PSS=-27, 95%CI=[-45, -8]) and the hands uncrossed conditions (PSS=-15, 95%CI=[ 30,6]), but significantly smaller in the hands crossed condition (PSS=-1, 95%CI=[-17, 15]). The difference between JNDs for controls and patients was comparable between the three hand arrangement conditions.
Limb (upper or lower) and side (left or right) did not contribute to the prediction of patient’s PSS or JND scores, but other clinical measures did.
Conclusion
The results provide the first empirical evidence for visual neglect in CRPS. This bias is not limited to visual information about the body because the PSS bias was largest for lights appearing on the table and did not differ between patients with upper and lower limb CRPS. The absence of a bias in the hands crossed condition may reflect an interaction of different spatial reference frames (i.e., attention to the body versus egocentric space) as has been demonstrated in stroke patients.
Larger JNDs in patients indicate decreased certainty when judging the order of visual targets, consistent with impaired body representation.
| Original language | English |
|---|---|
| Pages | 11-12 |
| DOIs | |
| Publication status | Published - 10 May 2016 |
| Event | British Pain Society Annual Society Meeting - Harrogate International Centre, Harrogate Duration: 10 May 2016 → 12 May 2016 |
Conference
| Conference | British Pain Society Annual Society Meeting |
|---|---|
| City | Harrogate |
| Period | 10/05/16 → 12/05/16 |