Sunday, March 20, 2016

A Detached Sense of Self Associated with Altered Neural Responses to Mirror Touch



Our bodily sense of self contributes to our personal feelings of awareness as a conscious being. How we see our bodies and move through space and feel touched by loved ones are integral parts of our identity. What happens when this sense of self breaks down? One form of dissolution is Depersonalization Disorder (DPD).1 Individuals with DPD feel estranged or disconnected from themselves, as if their bodies belong to someone else, and “they” are merely a detached observer. Or the self feels absent entirely. Other symptoms of depersonalization include emotional blunting, out-of-body experiences, and autoscopy.


Autoscopy for dummies - Antonin De Bemels (cc licence)


Transient symptoms of depersonalization can occur due to stress, anxiety, sleep deprivation, or drugs such as ketamine (a dissociative anesthetic) and hallucinogens (e.g., LSD, psilocybin). These experiences are much more common than the official diagnosis of DPD, which occurs in only 1-2% of the population.

Research by Olaf Blanke and colleagues (reviewed in Blanke et al., 2015) has tied bodily self-consciousness to the integration of multi-sensory signals in fronto-parietal and temporo-parietal regions of the brain.




The fragmentation or loss of an embodied self raises philosophically profound questions. Although the idea of “mind uploading” is preposterous in my view (whether via whole brain emulation or cryonics), proponents must seriously ask whether the uploaded consciousness will in any way resemble the living person from whom it arose.2 “Minds are not disembodied logical reasoning devices” (according to Andy Clark).  And...
Increasing evidence suggests that the basic foundations of the self lie in the brain systems that represent the body (Lenggenhager et al., 2012).

Lenggenhager et al. asked whether the loss of sensorimotor function alters body ownership and the sense of self. Persons with spinal cord injuries scored higher on Cambridge Depersonalization Scale (CDS) items such as “I have to touch myself to make sure that I have a body or a real existence.” This suggests that disconnecting the brain from somatosensory input can change phenomenological aspects of self-consciousness.




The Stranger in the Mirror

Patients with depersonalization not only feel a change in perception concerning the outside world, but they also have clear-cut changes concerning their own body.  ...  The patient sees his face in the mirror changed, rigid and distorted. His own voice seems strange and unfamiliar to him.  ...  It is in this respect especially remarkable that the estrangement concerning the outside world is often an estrangement in the optic sphere (Schilder, 1935, p. 139).

Depersonalization can involve perceptual distortions of bodily experience in different sensory modalities (e.g., vision, hearing, touch, and pain). Recent research has examined interactions between visual and somatosensory representations of self in the tactile mirroring paradigm (also called visual remapping of touch). Here, the participant views images of a person being touched (or not) while they themselves are touched. Tactile perception is enhanced by simultaneously receiving and observing the same stimulation, especially when the image is of oneself.


Are the symptoms of depersonalization associated with reduced or absent responses in the tactile mirroring paradigm? If so, at what stage of processing (early or late) does this occur? A new study recorded EEG to look at somatosensory evoked potential (SEP) responses to tactile stimuli during mirroring (Adler et al., 2016). The participants scored high (n=14) or low (n=13) on the CDS.

One SEP of interest was the P45, which occurs shortly (25-50 msec) after tactile stimulation. Although the spatial resolution of EEG does not allow firm conclusions about the neural generators, we know from invasive studies in epilepsy patients and animals that P45 originates in the primary somatosensory cortex (S1).

When the participants viewed the other-face, P45 did not differ on touch vs. no-touch trials. But the later N80 component was enhanced for touch vs. no-touch, and the enhancement was similar for low and high depersonalization (DP) participants.



Modified from Figs. 3 and 4 (Adler et al. 2016). SEPs in response to tactile stimuli for low DP (top) and high DP (bottom) while observing touch (thick line) or no-touch (thin line) on another person's face. SEPs are shown for components P45 and N80 at a cluster of central-parietal electrodes located over somatosensory cortex.


Results were different when subjects viewed images of themselves. P45 was enhanced in the low DP group when viewing themselves being touched (vs. no-touch trials). However, those with high DP scores did not show this P45 enhancement.



Modified from Figs. 3 and 4 (Adler et al. 2016). SEPs in response to tactile stimuli while observing touch (thick line) or no-touch (thin line) on the participant's own face. Red arrow indicates no self-mirror enhancement of P45.


These results suggest a very early disturbance in sensory integration of the self in depersonalization:
Measurable effects of mirroring for tactile events on the observer's own face may be absent over P45 because deficits in implicit self-related processing prevent the resulting visual enhancement of tactile processing from taking place in the context of self-related information. An alternative, or additional, explanation for the absence of P45 mirroring effects may be that seeing their own body causes depersonalised individuals to actively inhibit the processing of bodily stimulation via this pathway. This may cause feelings of disembodiment, and is akin to the suggestion that fronto-limbic inhibitory mechanisms acting on emotional processes cause the emotional numbing experienced in depersonalisation (Sierra and David, 2011).
[Although I'm not so sure how much “active inhibition” can occur within 25 msec...]




A later component (P200) did not show the expected effect in the high DP group, either. While these results are intriguing, we must keep in mind that this was a small study that requires replication.3


Our Bodies, Our Selves

Predictive coding models hypothesize that the anterior insular cortex (AIC) provides top-down input to somatosensory, autonomic, and visceral regions and plays a critical role in integrating exteroceptive and interoceptive signals (Seth et al., 2012; Allen et al., 2016). DPD is associated with “pathologically imprecise interoceptive predictive signals,” leading to a disruption of conscious presence (the subjective sense of reality of the world and of the self within the world). Here's the predictive coding model of conscious presence (Seth et al., 2012):
It has been suggested that DPD is associated with a suppressive mechanism grounded in fronto-limbic brain regions, notably the AIC, which “manifests subjectively as emotional numbing, and disables the process by which perception and cognition become emotionally colored, giving rise to a subjective feeling of unreality” (Sierra and David, 2011)...

In our model, DPD symptoms correspond to abnormal interoceptive predictive coding dynamics. ... the imprecise interoceptive prediction signals associated with DPD may result in hypoactivation of AIC since there is an excessive but undifferentiated suppression of error signals.

In contrast, Adler et al. (2016) adopt a very different (Freudian) view:
We speculate that the abnormalities related to depersonalisation may be based on a lack of mirroring interactions in early childhood. Several recent papers culminated in the idea that mirroring experiences in early life - the process of moving and being moved by others, both physically and affectively - give rise to our sense of bodily self... This bodily self forms the core of other forms of self-consciousness, from body ownership to the sense of agency and the ability to mentalise (e.g. Fonagy et al., 2007; Gallese & Sinigaglia, 2010; Markova and Legerstee, 2006; Stern, 1995). ...  Depersonalisation could be a potential consequence of such developmental experiences.

I don't buy it... none of the participants in their study had a clinical diagnosis, and we know nothing of their early childhood. In the end, any model of chronic DPD still has to account for the transient phenomena of disconnection and unreality experienced by so many of us.


Further Reading

Feeling Mighty Unreal: Derealization in Kleine-Levin Syndrome

Fright Week: The Stranger in the Mirror


Footnotes

1 In DSM-5, the syndrome is known as Depersonalization/Derealization Disorder. I wrote about the symptoms of derealization a subjective alteration in one's perception or experience of the outside world in another blog post.

2 For a discussion of the relevant issues, see The False Science of Cryonics and Silicon soul: The vain dream of electronic immortality.

3 Given the requirements for specialized equipment and a specialized population, I don't imagine this study is on the Many Labs or Replication Project lists.


References

Adler, J., Schabinger, N., Michal, M., Beutel, M., & Gillmeister, H. (2016). Is that me in the mirror? Depersonalisation modulates tactile mirroring mechanisms. Neuropsychologia DOI: 10.1016/j.neuropsychologia.2016.03.009

Allen M, Fardo F, Dietz MJ, Hillebrandt H, Friston KJ, Rees G, Roepstorff A. (2016). Anterior insula coordinates hierarchical processing of tactile mismatch responses. Neuroimage 127:34-43.

Blanke O, Slater M, Serino A. (2015). Behavioral, Neural, and Computational Principlesof Bodily Self-Consciousness. Neuron 88(1):145-66.

Lenggenhager, B., Pazzaglia, M., Scivoletto, G., Molinari, M., & Aglioti, S. (2012). The Sense of the Body in Individuals with Spinal Cord Injury. PLoS ONE, 7 (11) DOI: 10.1371/journal.pone.0050757

Schilder, P. (1935). The Image and Appearance of the Human Body. London: Kagan, Paul, Trench, Trubner & Co.

Seth AK, Suzuki K, Critchley HD. (2012). An interoceptive predictive coding model of conscious presence. Front Psychol. 2:395.




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