Specificity and coherence of body representations

Bodily illusions differently affect body representations underlying perception and action. We investigated whether this task dependence reflects two distinct dimensions of embodiment: the sense of agency and the sense of the body as a coherent whole. In experiment 1 the sense of agency was manipulated by comparing active versus passive movements during the induction phase in a video rubber hand illusion (vRHI) setup. After induction, proprioceptive biases were measured both by perceptual judgments of hand position, as well as by measuring end-point accuracy of subjects' active pointing movements to an external object with the affected hand. The results showed, first, that the vRHI is largely perceptual: passive perceptual localisation judgments were altered, but end-point accuracy of active pointing responses with the affected hand to an external object was unaffected. Second, within the perceptual judgments, there was a novel congruence effect, such that perceptual biases were larger following passive induction of vRHI than following active induction. There was a trend for the converse effect for pointing responses, with larger pointing bias following active induction. In experiment 2, we used the traditional RHI to investigate the coherence of body representation by synchronous stimulation of either matching or mismatching fingers on the rubber hand and the participant's own hand. Stimulation of matching fingers induced a local proprioceptive bias for only the stimulated finger, but did not affect the perceived shape of the hand as a whole. In contrast, stimulation of spatially mismatching fingers eliminated the RHI entirely. The present results show that (i) the sense of agency during illusion induction has specific effects, depending on whether we represent our body for perception or to guide action, and (ii) representations of specific body parts can be altered without affecting perception of the spatial configuration of the body as a whole

Пам’яті Ірини Миколаївни Алексєєвої

На 77-му ропі життя, 9 лютого 2011 р. відійшла від нас знана і шанована людина, доктор біологічних наук, завідувач відділу імунології і цитотоксичних сироваток Інституту фізіології ім. О.О. Богомольця НАН України, Ірина Миколаївна Алексєєва

Bodies in the Brain : More than the weighted sum of their parts

The main question of this thesis was: Can we dissociate multiple body representations in the healthy brain? Patient studies have already shown a dichotomy between the perceptual representation used for localizing a body part (body image) versus the motor representation used for moving a body part (body schema). Here it is shown for the first time that there is also a similar dichotomy in healthy individuals, as revealed by task dependency of bodily illusions. This dissociation between motor and perception tasks relied heavily on the high susceptibility of the body image, versus robustness of the body schema. To investigate whether the impermeability of the motoric body representation was dependent on the type of induction of the bodily illusion, feeling of agency was manipulated. Even active movement during induction could however not affect the body schema. Although motor actions themselves thus seemed robust to illusion, its possible mediating effect on subsequent perceptual body localization judgments was investigated. Results showed a reduction in the strength of the bodily illusion (in this case the rubber hand illusion) that was dependent on the number of movements made with the illuded hand. In other words, the more (new) proprioceptive information was provided about the illuded limb, the smaller the perceived relocation of the illuded hand (as measured by perceptual judgments). However, even though the strength of the illusion on the body image was reduced by preceding motor responses, it did not erase the effect of the illusion completely. Consequently, the main question Can we dissociate multiple body representations in the healthy brain? can be answered affirmatively. However, the main line of reasoning behind the used paradigm - significantly different responses are subserved by dissociable body representations - becomes problematic when significant different responses within the same type of task can be identified. In that case, this line of reasoning runs the risk of dissociating numerous body representations. Therefore a more dynamic angle is suggested, focusing on the question of how these different body representations are created, therefore looking more closely into the weighting of sensory information. Although this approach has its own pitfalls and does not answer the questions of how many body representations there are, it might lead to relevant new insight when combined with other fields of research and paradigms. As an example, a loss of proprioceptive influence on a visual afterimage is for the first time demonstrated, revealing a critical mediating role of feeling of ownership. This shows that studying the integration of proprioceptive and visual information, while keeping in mind the (dynamic) representation of the body and bodily sensations like feeling of ownership, might cast new light on the weighting of multisensory information and consequently on the way the representation of the body is built

A case of illusory own-body perceptions after transcranial magnetic stimulation of the cerebellum

Item does not contain fulltextIllusory own-body perceptions are 'body in space' misinterpretations of the brain and belong to the class of out-of-body experiences wherein the angular gyrus seems importantly implicated. In the present study additional cerebellum involvement in illusory own-body perceptions was investigated in a healthy young female right-handed volunteer. Transcranial magnetic stimulation (TMS) was applied over the cerebellum. Placebo cerebellum TMS and occipital TMS served as control conditions. Illusory own-body perceptions accompanied by electric brain activity over the somatosensory cortex were only observed after cerebellum TMS. The data provide the first evidence that the cerebellum might be involved in a neuronal network underlying illusory own-body perceptions

Perception of emotional facial expressions at different intensities in early-symptomatic Huntington's Disease

Item does not contain fulltextBACKGROUND: While there is abundant evidence that patients with Huntington's disease (HD) have an impairment in the recognition of the emotional facial expression of disgust, previous studies have only examined emotion perception using full-blown facial expressions. OBJECTIVE: The current study examines the perception of facial emotional expressions in HD at different levels of intensity to investigate whether more subtle deficits can be detected, possible also in other emotions. METHOD: We compared early symptomatic HD patients with healthy matched controls on emotion perception, presenting short video clips of a neutral face changing into one of the six basic emotions (happiness, anger, fear, surprise, disgust and sadness) with increasing intensity. Overall face perception ability as well as depressive symptoms were taken into account. RESULTS: A specific impairment in recognizing the emotions disgust and anger was found, which was present even at low emotion intensities. CONCLUSION: These results extend previous findings and support the use of more sensitive emotion perception paradigms, which enable the detection of subtle neurobehavioral deficits even in the pre- and early symptomatic stages of the disease.4 p