The Cutaneous Rabbit Illusion Affects Human Primary Sensory Cortex Somatotopically

UCL Institute of Cognitive Neuroscience, Department of Psychology, University College London, London, United Kingdom.
PLoS Biology (Impact Factor: 9.34). 04/2006; 4(3):e69. DOI: 10.1371/journal.pbio.0040069
Source: PubMed


We used functional magnetic resonance imaging (fMRI) to study neural correlates of a robust somatosensory illusion that can dissociate tactile perception from physical stimulation. Repeated rapid stimulation at the wrist, then near the elbow, can create the illusion of touches at intervening locations along the arm, as if a rabbit hopped along it. We examined brain activity in humans using fMRI, with improved spatial resolution, during this version of the classic cutaneous rabbit illusion. As compared with control stimulation at the same skin sites (but in a different order that did not induce the illusion), illusory sequences activated contralateral primary somatosensory cortex, at a somatotopic location corresponding to the filled-in illusory perception on the forearm. Moreover, the amplitude of this somatosensory activation was comparable to that for veridical stimulation including the intervening position on the arm. The illusion additionally activated areas of premotor and prefrontal cortex. These results provide direct evidence that illusory somatosensory percepts can affect primary somatosensory cortex in a manner that corresponds somatotopically to the illusory percept.

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Available from: Felix Blankenburg
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    • "This hypothesis is consistent with observations reported in a recent neurophysiological study investigating the neural correlates of Aristotle’s illusion in healthy subjects [44]. As revealed in that study and as found in previous investigations on other types of tactile illusions [45], [46], activity in the primary somatosensory cortex reflects the illusory doubling perception rather than the physical characteristics of the tactile stimuli. "
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    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.
    Full-text · Article · Feb 2014 · PLoS ONE
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    • "This dissociation of tactile perception from physical stimulation is sometimes known as the cutaneous rabbit illusion, in which one experiences a sensation as if a tiny rabbit is hopping along the arm from wrist to elbow. We exploited the established somatotopy of the primary sensory cortex in humans and used fMRI to examine signals in the sensory cortex corresponding to the location of the wrist, elbow, or intervening forearm while people were stimulated in a fashion that induced the illusion.11 We compared signals when the illusion was elicited with those produced by control stimulation at the same sites on the wrist and elbow, but now in a different order that did not induce the cutaneous rabbit illusion. "
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    ABSTRACT: Jon Driver's scientific work was characterized by an innovative combination of new methods for studying mental processes in the human brain in an integrative manner. In our collaborative work, he applied this approach to the study of attention and awareness, and their relationship to neural activity in the human brain. Here I review Jon's scientific work that relates to the neural basis of human consciousness, relating our collaborative work to a broader scientific context. I seek to show how his insights led to a deeper understanding of the causal connections between distant brain structures that are now believed to characterize the neural underpinnings of human consciousness.
    Full-text · Article · Aug 2013 · Annals of the New York Academy of Sciences
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    • "However, an alternative interpretation is that the findings were the result of the placebo effect; it is possible that a sensory expectation resulting from a priori knowledge of the reflex area influenced the cognitive processing of the perceived reflexological stimulation. Blankenburg [15] reported that a somatosensory illusion called the “cutaneous rabbit” [16] evoked cortical activity in SI that somatotopically corresponded to the illusory percepts. Furthermore, this illusion has been shown to occur outside the body using a stick held across the left and right index fingers [17], indicating top-down cognitive processing such as might be observed in a body–object interaction when processing a tactile sensation. "
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    ABSTRACT: Background Reflexology is an alternative medical practice that produces beneficial effects by applying pressure to specific reflex areas. Our previous study suggested that reflexological stimulation induced cortical activation in somatosensory cortex corresponding to the stimulated reflex area; however, we could not rule out the possibility of a placebo effect resulting from instructions given during the experimental task. We used functional magnetic resonance imaging (fMRI) to investigate how reflexological stimulation of the reflex area is processed in the primary somatosensory cortex when correct and pseudo-information about the reflex area is provided. Furthermore, the laterality of activation to the reflexological stimulation was investigated. Methods Thirty-two healthy Japanese volunteers participated. The experiment followed a double-blind design. Half of the subjects received correct information, that the base of the second toe was the eye reflex area, and pseudo-information, that the base of the third toe was the shoulder reflex area. The other half of the subjects received the opposite information. fMRI time series data were acquired during reflexological stimulation to both feet. The experimenter stimulated each reflex area in accordance with an auditory cue. The fMRI data were analyzed using a conventional two-stage approach. The hemodynamic responses produced by the stimulation of each reflex area were assessed using a general linear model on an intra-subject basis, and a two-way repeated-measures analysis of variance was performed on an intersubject basis to determine the effect of reflex area laterality and information accuracy. Results Our results indicated that stimulation of the eye reflex area in either foot induced activity in the left middle postcentral gyrus, the area to which tactile sensation to the face projects, as well as in the postcentral gyrus contralateral foot representation area. This activity was not affected by pseudo information. The results also indicate that the relationship between the reflex area and the projection to the primary somatosensory cortex has a lateral pattern that differs from that of the actual somatotopical representation of the body. Conclusion These findings suggest that a robust relationship exists between neural processing of somatosensory percepts for reflexological stimulation and the tactile sensation of a specific reflex area.
    Full-text · Article · May 2013 · BMC Complementary and Alternative Medicine
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