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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

Additional control conditions in PD patients and healthy controls.The columns represent the mean percentage of correct response averaged across all the digit pairs for the affected and the less/unaffected hand. Control1 refers to the control condition with crossed fingers and one sphere on one fingertip, Control2 refers to the control condition with parallel fingers and two spheres simultaneously placed on the two fingertips. The bars represent the standard error. The two groups showed high and comparable number of correct responses in each additional control condition.
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pone-0088686-g003: Additional control conditions in PD patients and healthy controls.The columns represent the mean percentage of correct response averaged across all the digit pairs for the affected and the less/unaffected hand. Control1 refers to the control condition with crossed fingers and one sphere on one fingertip, Control2 refers to the control condition with parallel fingers and two spheres simultaneously placed on the two fingertips. The bars represent the standard error. The two groups showed high and comparable number of correct responses in each additional control condition.

Mentions: Finally, the analysis of the additional control conditions on both hands did not reveal significant effect of group (affected hand: F (1,28)  = 0.18; P = 0.679; less/unaffected hand: F (1,28)  = 2.15, P = 0.153), or control condition (affected hand: F (1,28)  = 0.14, P = 0.711; less/unaffected hand: F (1,28)  = 2.15, P = 0.153). Furthermore, the interaction group*control condition was not significant (affected hand: F (1,28)  = 1.26, P = 0.271; less/unaffected hand: F (1,28)  = 2.15, P = 0.153). Notably, the fact that the percentage of correct response was overall high in both the Control1-crossed condition (99.4%±0.02) and Control2-parallel condition (99.6%±0.2%), confirms that the finger position per se does not affect tactile perception (Figure 3).


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)

Additional control conditions in PD patients and healthy controls.The columns represent the mean percentage of correct response averaged across all the digit pairs for the affected and the less/unaffected hand. Control1 refers to the control condition with crossed fingers and one sphere on one fingertip, Control2 refers to the control condition with parallel fingers and two spheres simultaneously placed on the two fingertips. The bars represent the standard error. The two groups showed high and comparable number of correct responses in each additional control condition.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0088686-g003: Additional control conditions in PD patients and healthy controls.The columns represent the mean percentage of correct response averaged across all the digit pairs for the affected and the less/unaffected hand. Control1 refers to the control condition with crossed fingers and one sphere on one fingertip, Control2 refers to the control condition with parallel fingers and two spheres simultaneously placed on the two fingertips. The bars represent the standard error. The two groups showed high and comparable number of correct responses in each additional control condition.
Mentions: Finally, the analysis of the additional control conditions on both hands did not reveal significant effect of group (affected hand: F (1,28)  = 0.18; P = 0.679; less/unaffected hand: F (1,28)  = 2.15, P = 0.153), or control condition (affected hand: F (1,28)  = 0.14, P = 0.711; less/unaffected hand: F (1,28)  = 2.15, P = 0.153). Furthermore, the interaction group*control condition was not significant (affected hand: F (1,28)  = 1.26, P = 0.271; less/unaffected hand: F (1,28)  = 2.15, P = 0.153). Notably, the fact that the percentage of correct response was overall high in both the Control1-crossed condition (99.4%±0.02) and Control2-parallel condition (99.6%±0.2%), confirms that the finger position per se does not affect tactile perception (Figure 3).

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