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Aristotle's illusion in Parkinson's disease: evidence for normal interdigit tactile perception.

Fiorio M, Marotta A, Ottaviani S, Pozzer L, Tinazzi M - PLoS ONE (2014)

Bottom Line: Recently, we found a selective reduction of tactile perception (Aristotle's illusion, the illusory doubling sensation of one object when touched with crossed fingers) in the affected hand of patients with focal hand dystonia.This suggests that reduced tactile illusion might be a specific feature of this type of dystonia and could be due to abnormal somatosensory cortical activation.The retained tactile illusion in PD and its reduction in focal hand dystonia suggest that the basal ganglia, which are dysfunctional in both PD and dystonia, may not be causally involved in this function.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurological and Movement Sciences, University of Verona, Verona, Italy.

ABSTRACT
Sensory alterations, a common feature of such movement disorders as Parkinson's disease (PD) and dystonia, could emerge as epiphenomena of basal ganglia dysfunction. Recently, we found a selective reduction of tactile perception (Aristotle's illusion, the illusory doubling sensation of one object when touched with crossed fingers) in the affected hand of patients with focal hand dystonia. This suggests that reduced tactile illusion might be a specific feature of this type of dystonia and could be due to abnormal somatosensory cortical activation. The aim of the current study was to investigate whether Aristotle's illusion is reduced in the affected hand of patients with PD. We tested 15 PD patients, in whom motor symptoms were mainly localised to one side of the body, and 15 healthy controls. Three pairs of fingers were tested in crossed (evoking the illusion) or parallel position (not evoking the illusion). A sphere was placed in the contact point between the two fingers and the blindfolded participants had to say whether they felt one or two stimuli. Stimuli were applied on the affected and less or unaffected side of the PD patients. We found no difference in illusory perception between the PD patients and the controls, nor between the more affected and less/unaffected side, suggesting that Aristotle's illusion is preserved in PD. The retained tactile illusion in PD and its reduction in focal hand dystonia suggest that the basal ganglia, which are dysfunctional in both PD and dystonia, may not be causally involved in this function. Instead, the level of activation between digits in the somatosensory cortex may be more directly involved. Finally, the similar percentage of illusion in the more affected and less or unaffected body sides indicates that the illusory perception is not influenced by the presence or amount of motor symptoms.

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Related in: MedlinePlus

Aristotle’s illusion in patients with Parkinson’s disease (PD) versus healthy controls.The columns represent the mean percentage of illusion perceived in all the tested digit-pairs of both the affected and the less/unaffected hand. The bars represent the standard error. In the crossed position (A) the patients perceived the illusion like the controls. There were no differences between the two groups also in the parallel finger position (B). Hence, contrary to other aspects of somatosensory perception, Aristotle’s illusion is preserved in PD.
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pone-0088686-g002: Aristotle’s illusion in patients with Parkinson’s disease (PD) versus healthy controls.The columns represent the mean percentage of illusion perceived in all the tested digit-pairs of both the affected and the less/unaffected hand. The bars represent the standard error. In the crossed position (A) the patients perceived the illusion like the controls. There were no differences between the two groups also in the parallel finger position (B). Hence, contrary to other aspects of somatosensory perception, Aristotle’s illusion is preserved in PD.

Mentions: As expected, the main analysis showed that the finger position factor was significant (F (1,28)  = 435.2, P<0.001). This was due to an overall higher percentage of the “two stimuli” response in the crossed (mean ± standard error of the mean, 93±2.3%) than in the parallel finger position (16.7±3.3%) (Figure 2A, B). The finger pair factor was also significant (F (2,56)  = 21.3, P<0.001), due to a higher percentage of the “two stimuli” response in the finger pair D2-D4 (65.3±3.9%) compared to D2-D3 (47.2±1.9%, P<0.001) and to D4-D5 (52±2%, P = 0.001). Moreover, the interaction finger position × finger pair was also significant (F (2,56) = 18.3, P<0.001). Post-hoc comparisons showed that in the parallel finger position the percentage of the “two stimuli” response was higher in the finger pair D2-D4 (37.5±6.7%) compared to D2-D3 (3.5±1.4%, P<0.001) and D4-D5 (9.2±3.5%, P<0.001) (Figure 2B)”. The effects of group and body side and all the other interactions between the factors were not significant (P>0.333); therefore, the patients perceived the illusion like the healthy controls, independently of whether the stimulus was applied to the affected or the unaffected side.


Aristotle's illusion in Parkinson's disease: evidence for normal interdigit tactile perception.

Fiorio M, Marotta A, Ottaviani S, Pozzer L, Tinazzi M - PLoS ONE (2014)

Aristotle’s illusion in patients with Parkinson’s disease (PD) versus healthy controls.The columns represent the mean percentage of illusion perceived in all the tested digit-pairs of both the affected and the less/unaffected hand. The bars represent the standard error. In the crossed position (A) the patients perceived the illusion like the controls. There were no differences between the two groups also in the parallel finger position (B). Hence, contrary to other aspects of somatosensory perception, Aristotle’s illusion is preserved in PD.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3921216&req=5

pone-0088686-g002: Aristotle’s illusion in patients with Parkinson’s disease (PD) versus healthy controls.The columns represent the mean percentage of illusion perceived in all the tested digit-pairs of both the affected and the less/unaffected hand. The bars represent the standard error. In the crossed position (A) the patients perceived the illusion like the controls. There were no differences between the two groups also in the parallel finger position (B). Hence, contrary to other aspects of somatosensory perception, Aristotle’s illusion is preserved in PD.
Mentions: As expected, the main analysis showed that the finger position factor was significant (F (1,28)  = 435.2, P<0.001). This was due to an overall higher percentage of the “two stimuli” response in the crossed (mean ± standard error of the mean, 93±2.3%) than in the parallel finger position (16.7±3.3%) (Figure 2A, B). The finger pair factor was also significant (F (2,56)  = 21.3, P<0.001), due to a higher percentage of the “two stimuli” response in the finger pair D2-D4 (65.3±3.9%) compared to D2-D3 (47.2±1.9%, P<0.001) and to D4-D5 (52±2%, P = 0.001). Moreover, the interaction finger position × finger pair was also significant (F (2,56) = 18.3, P<0.001). Post-hoc comparisons showed that in the parallel finger position the percentage of the “two stimuli” response was higher in the finger pair D2-D4 (37.5±6.7%) compared to D2-D3 (3.5±1.4%, P<0.001) and D4-D5 (9.2±3.5%, P<0.001) (Figure 2B)”. The effects of group and body side and all the other interactions between the factors were not significant (P>0.333); therefore, the patients perceived the illusion like the healthy controls, independently of whether the stimulus was applied to the affected or the unaffected side.

Bottom Line: Recently, we found a selective reduction of tactile perception (Aristotle's illusion, the illusory doubling sensation of one object when touched with crossed fingers) in the affected hand of patients with focal hand dystonia.This suggests that reduced tactile illusion might be a specific feature of this type of dystonia and could be due to abnormal somatosensory cortical activation.The retained tactile illusion in PD and its reduction in focal hand dystonia suggest that the basal ganglia, which are dysfunctional in both PD and dystonia, may not be causally involved in this function.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurological and Movement Sciences, University of Verona, Verona, Italy.

ABSTRACT
Sensory alterations, a common feature of such movement disorders as Parkinson's disease (PD) and dystonia, could emerge as epiphenomena of basal ganglia dysfunction. Recently, we found a selective reduction of tactile perception (Aristotle's illusion, the illusory doubling sensation of one object when touched with crossed fingers) in the affected hand of patients with focal hand dystonia. This suggests that reduced tactile illusion might be a specific feature of this type of dystonia and could be due to abnormal somatosensory cortical activation. The aim of the current study was to investigate whether Aristotle's illusion is reduced in the affected hand of patients with PD. We tested 15 PD patients, in whom motor symptoms were mainly localised to one side of the body, and 15 healthy controls. Three pairs of fingers were tested in crossed (evoking the illusion) or parallel position (not evoking the illusion). A sphere was placed in the contact point between the two fingers and the blindfolded participants had to say whether they felt one or two stimuli. Stimuli were applied on the affected and less or unaffected side of the PD patients. We found no difference in illusory perception between the PD patients and the controls, nor between the more affected and less/unaffected side, suggesting that Aristotle's illusion is preserved in PD. The retained tactile illusion in PD and its reduction in focal hand dystonia suggest that the basal ganglia, which are dysfunctional in both PD and dystonia, may not be causally involved in this function. Instead, the level of activation between digits in the somatosensory cortex may be more directly involved. Finally, the similar percentage of illusion in the more affected and less or unaffected body sides indicates that the illusory perception is not influenced by the presence or amount of motor symptoms.

Show MeSH
Related in: MedlinePlus