Fractionating the unitary notion of dissociation: disembodied but not embodied dissociative experiences are associated with exocentric perspective-taking

[Ketamine Augmented Psychotherapy (KAP) in mood disorder: User guide]

Ketamine, a non-competitive NMDA receptor antagonist, is used as a fast-acting antidepressant therapy in depressive disorders. This treatment provokes dissociative effects associating derealization and depersonalization, and a synaptogenic signaling cascade promoting brain plasticity. Despite several preliminary studies suggesting the usefulness of its combination with psychotherapy, administration of ketamine isn't generally combined with per- and post-infusion psychotherapy protocols in its clinical antidepressant use. However, the phenomenology of psychodysleptic experiences and the synaptogenic effect could potentiate cognitive and behavioral therapies (CBT). In this article, we purpose a practical protocol to Ketamine Augmented Psychotherapy (KAP) synthesizing contemporary data from the literature and our clinical experience. We detail proposals for clinical practice, and propose four important steps for the use of a psychodysleptic molecule for antidepressant purposes: preparation, administration, integration, and prolongation. Finally, we discuss the limits and prospects of this combination in the management of mood disorders.

The depersonalized brain: New evidence supporting a distinction between depersonalization and derealization from discrete patterns of autonomic suppression observed in a non-clinical sample

Depersonalization and Derealization are characterised by feelings of detachment from one's bodily self/surroundings and a general emotional numbness. We explored predisposition to trait-based experiences of depersonalization/derealization-type experiences and autonomic arousal toward simulated body-threats, which were delivered to the participant's own body (i.e. Self) and when observed being delivered to another individual (i.e. Other). Ninety participants took part in an "Implied Body-Threat Illusion" task (Dewe, Watson, & Braithwaite, 2016) and autonomic arousal was recorded via standardised skin conductance responses and finger temperature. Autonomic suppression in response to threats delivered to the Self correlated with increases in trait-based depersonalization-type experiences. In contrast, autonomic suppression for threats delivered to Others correlated with trait-based derealization-like experiences. Body-temperature and anticipatory arousal did not correlate reliably with predisposition to depersonalization- or derealization-type experiences. The theoretical implications of these findings are discussed in terms of a fronto-limbic autonomic suppression mechanism.

Transcranial direct current stimulation of the right temporoparietal junction impairs third-person perspective taking

Given the current debates about the precise functional role of the right temporoparietal junction (rTPJ) in egocentric and exocentric perspective taking, in the present study we manipulated activity in the rTPJ to investigate the effects on a spatial perspective-taking task. Participants engaged in a mental body transformation task, requiring them to mentally rotate their own body to the position of an avatar, while undergoing anodal, cathodal, or sham transcranial direct current stimulation (tDCS) of the rTPJ. As a control task, participants judged the laterality of a stimulus feature with respect to a fixation cross on the screen. For the first half of the experiment (only during online tDCS), a task-selective effect of tDCS was observed, reflected in slower reaction times following anodal than following cathodal and sham tDCS for the mental body transformation task, but not for the control task. The effects of tDCS were most pronounced for stimuli implying a more difficult mental body transformation. No effects of tDCS were observed during the second half of the experiment. The effects of tDCS were most pronounced for participants scoring low on aberrant perceptual beliefs and spiritual transcendence, suggesting a relation between third-person perspective taking and bodily and perceptual experiences. The finding that anodal stimulation of the rTPJ impairs third-person perspective taking indicates a key role of this region in exocentric spatial processing.

Deliberate and spontaneous sensations of disembodiment: capacity or flaw?

INTRODUCTION

Hallucinations that involve shifts in the subjectively experienced location of the self, have been termed "out-of-body experiences" (OBEs). Early psychiatric accounts cast OBEs as a specific instance of depersonalisation and derealisation disorder (DPD-DR). However, during feelings of alienation and lack of body realism in DPD-DR the self is experienced within the physical body. Deliberate forms of "disembodiment" enable humans to imagine another's visuo-spatial perspective taking (VPT), thus, if a strong relationship between deliberate and spontaneous forms of disembodiment could be revealed, then uncontrolled OBEs could be "the other side of the coin" of a uniquely human capacity.

METHODS

We present a narrative review of behavioural and neuroimaging work emphasising methodological and theoretical aspects of OBE and VPT research and a potential relationship.

RESULTS

Results regarding a direct behavioural relationship between VPT and OBE are mixed and we discuss reasons by pointing out the importance of using realistic tasks and recruiting genuine OBEers instead of general DPD-DR patients. Furthermore, we review neuroimaging evidence showing overlapping neural substrates between VPT and OBE, providing a strong argument for a relationship between the two processes.

CONCLUSIONS

We conclude that OBE should be regarded as a necessary implication of VPT ability in humans, or even as a necessary and potentially sufficient condition for the evolution of VPT.

Embodied mental rotation: a special link between egocentric transformation and the bodily self

This experiment investigated the influence of motor expertise on object-based versus egocentric transformations in a chronometric mental rotation task using images of either the own or another person’s body as stimulus material. According to the embodied cognition viewpoint, we hypothesized motor-experts to outperform non-motor experts specifically in the egocentric condition because of higher kinesthetic representation and motor simulations compared to object-based transformations. In line with this, we expected that images of the own body are solved faster than another person’s body stimuli. Results showed a benefit of motor expertise and representations of another person’s body, but only for the object-based transformation task. That is, this other-advantage diminishes in egocentric transformations. Since motor experts did not show any specific expertise in rotational movements, we concluded that using human bodies as stimulus material elicits embodied spatial transformations, which facilitates performance exclusively for egocentric transformations. Regarding stimulus material, the other-advantage ascribed to increased self-awareness-consciousness distracting attention-demanding resources, disappeared in the egocentric condition. This result may be due to the stronger link between the bodily self and motor representations compared to that emerging in object-based transformations.

A cross-culture, cross-gender comparison of perspective taking mechanisms

Being able to judge another person's visuo-spatial perspective is an essential social skill, hence we investigated the generalizability of the involved mechanisms across cultures and genders. Developmental, cross-species, and our own previous research suggest that two different forms of perspective taking can be distinguished, which are subserved by two distinct mechanisms. The simpler form relies on inferring another's line-of-sight, whereas the more complex form depends on embodied transformation into the other's orientation in form of a simulated body rotation. Our current results suggest that, in principle, the same basic mechanisms are employed by males and females in both, East-Asian (EA; Chinese) and Western culture. However, we also confirmed the hypothesis that Westerners show an egocentric bias, whereas EAs reveal an other-oriented bias. Furthermore, Westerners were slower overall than EAs and showed stronger gender differences in speed and depth of embodied processing. Our findings substantiate differences and communalities in social cognition mechanisms across genders and two cultures and suggest that cultural evolution or transmission should take gender as a modulating variable into account.

Shared action spaces: a basis function framework for social re-calibration of sensorimotor representations supporting joint action

The article explores the possibilities of formalizing and explaining the mechanisms that support spatial and social perspective alignment sustained over the duration of a social interaction. The basic proposed principle is that in social contexts the mechanisms for sensorimotor transformations and multisensory integration (learn to) incorporate information relative to the other actor(s), similar to the “re-calibration” of visual receptive fields in response to repeated tool use. This process aligns or merges the co-actors’ spatial representations and creates a “Shared Action Space” (SAS) supporting key computations of social interactions and joint actions; for example, the remapping between the coordinate systems and frames of reference of the co-actors, including perspective taking, the sensorimotor transformations required for lifting jointly an object, and the predictions of the sensory effects of such joint action. The social re-calibration is proposed to be based on common basis function maps (BFMs) and could constitute an optimal solution to sensorimotor transformation and multisensory integration in joint action or more in general social interaction contexts. However, certain situations such as discrepant postural and viewpoint alignment and associated differences in perspectives between the co-actors could constrain the process quite differently. We discuss how alignment is achieved in the first place, and how it is maintained over time, providing a taxonomy of various forms and mechanisms of space alignment and overlap based, for instance, on automaticity vs. control of the transformations between the two agents. Finally, we discuss the link between low-level mechanisms for the sharing of space and high-level mechanisms for the sharing of cognitive representations.