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Cognitive Neuroscience (Fach) / Body processing (Lektion)

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• What is special about the neurons in ventral intraparietal area (VIP) and the polysensory zone in premotor cortex (PZ) in the macaque monkey? There are multisensory neurons for peripersonal space. These have tactile receptive fields, but also visual (and sometimes auditory) receptive fields that are linked to the skin site of the tactile reference frame.
• What may be the use of neurons that respond to peripersonal space? Research has shown that stimulating neurons in VIP and PZ activates defensive behavior in monkeys. Also these neurons fired more strongly when objects were moving towards the body than when they were moving away from the body. This indicates that a response is executed (defense, run away) when something enters the peripersonal space to protect the individual. They may also be related to more complex functions of social operation. This is indicated by a study on the CCE that found that participants were able to ignore the concurrent visual stimuli when they had a partner who was close by (within pps) and performed a task related to the visual distractors. 
• What is the crossmodal congruency task? The subject receives tactile stimulation on two sites of the body/hand (e.g., index finger and thumb) and is asked to judge where the stimulation occurres. At the same time visual stimuli are presented either at the site where the tactile stimulus appeares or at the site where the other tactile target is located (the one that is not activated in the trial). Even though participants are asked to ignore the visual stimuli, their reaction times are faster when the visual stimulus is presented at the site of the tactile stimulation. Reaction times are slower when the visual stimulus is presented at the site of the non-activated tactile stimulus. The difference in reaction times and errors between tactile-visual congruent conditions and tactile-visual incongruent conditions is the crossmodal congruency effect.
• What conclusions can be drawn from the crossmodal congruency effect? The CCE indicates that when visual and tactile stimuli are presented close to each other, they are processed together by the multisensory peripersonal space neurons. This conclusion is further validated by the finding that the CCE is much smaller when visual distractor stimuli are presented far from the tactile stimuli, even when the visual stimui are presented at the same position in space (and the tactile stimuli are moved, e.g. by changing the position of the hand).
• Describe the homunculus and new results on neural mapping. Previously (with short stimulation of motor cortex) it was found that the motor cortex represented a “body map” and was organized in a somatotopical manner (homunculus; regions next to each other in cortex are also next to each other on body). However, prolonged (500ms) stimulation of motor and premotor areas evoked coordinated actions. It seems as if these responses are organized in zones that span motor and premotor cortex. These may be mapped by other criteria, such as action maps, target location maps, etc.,  and show that neural organization depends on multiple constraints.
• What are typical differences of real and experimentally induced out-of-body experiences? Disembodiment of self to extracorporeal location vs. no overt disembodiment Extracorporeal visuospatial perspective vs. no change of visuospatial perspective Sight of own body from the illusory self-location vs. very similar to clinical condition of heautoscopy.
• Name four conditions for the occurrence of changes in bodily self-consciousness. Multisensory integration (synchronous stimulation across senses from outside and body-related) Top-down body knowledge (position an shape) Peripersonal space (close to body, not as relevant in out-of-body illusions). Embodiment (synchronous multisensory stimulation, modulates what is perceived peripersonal).
• How can the RHI be measured? Questionnaire (touch is perceived to be in location of the rubber hand; perceived touch is felt to be caused by the seen object touching RH; RH feels like own hand) Proprioceptive drift (the indicated location of the hand is biased towards the location of the RH) Hand actions (movement is affected in a way consistent with the RH being the start point of the movement).
• What is an explanation for the ability of tool use on a neuronal level? Why are tools not treated as “own body”? The receptive field of neurons that respond to the space close around the monkey’s body expanded after tool use (retrieval of food with a rake). For distal-type neurons, receptive fields included the space around the hand (before tool use) and expanded to include the rake (after tool use). For proximal-type neurons they included the space that could be reached by the hand (before tool use) and the extended region that could be reached with the rake (after tool use). Thus, these neurons seem to respond to space that can be manipulated by the individual and enable the use of tools. However, it is unlikely that these tools are incorporated into bodily self-consciousness, as the top-down body knowledge constraint is not met (the tool does not look like the arm/hand). Nevertheless, this might hold true for prostheses.

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