Experimentally induced limb-disownership in mixed reality.

The seemingly stable construct of our bodily self depends on the continued, successful integration of multisensory feedback about our body, rather than its purely physical composition. Accordingly, pathological disruption of such neural processing is linked to striking alterations of the bodily self, ranging from limb misidentification to disownership, and even the desire to amputate a healthy limb. While previous embodiment research has relied on experimental setups using supernumerary limbs in variants of the Rubber Hand Illusion, we here used Mixed Reality to directly manipulate the feeling of ownership for one's own, biological limb. Using a Head-Mounted Display, participants received visual feedback about their own arm, from an embodied first-person perspective. In a series of three studies, in independent cohorts, we altered embodiment by providing visuotactile feedback that could be synchronous (control condition) or asynchronous (400 ms delay, Real Hand Illusion). During the illusion, participants reported a significant decrease in ownership of their own limb, along with a lowered sense of agency. Supporting the right-parietal body network, we found an increased illusion strength for the left upper limb as well as a modulation of the feeling of ownership during anodal transcranial direct current stimulation. Extending previous research, these findings demonstrate that a controlled, visuotactile conflict about one's own limb can be used to directly and systematically modulate ownership - without a proxy. This not only corroborates the malleability of body representation but questions its permanence. These findings warrant further exploration of combined VR and neuromodulation therapies for disorders of the bodily self.

Patterns of cortisol reactivity to laboratory stress.

Cortisol responses to a laboratory stress protocol were investigated in 82 male firefighters. Saliva samples were collected during an adaptation period beginning between 9 and 10 am, and then at the end of each of six 10-min trials (a mental arithmetic task, an inter-task recovery period, a speech task, and three recovery periods). Individual differences in the mean cortisol response to the stress tasks were characterized by variation in the direction of the response, as well as the size of the response. Neither pre-stress cortisol levels nor responses were correlated with cardiovascular and mood responses. Cortisol levels before stress task presentation were negatively correlated with recent stress severity. Larger mean cortisol responses were associated with lower reports of recent stress exposure, lower negative affect scores, and a coping style characterized less experience of anger, more control over anger expression, and a tendency to screen out threatening information in stressful situations. Thus, increased cortisol activity was associated with less recent stress exposure and a more adaptive behavioral style than for those whose cortisol levels fell or were largely unchanged in response to a laboratory stressor.