Body perception and brain plasticity in blind and sighted individuals

Lack of vision is associated with large-scale brain plasticity. Vision, touch, proprioception, interoception, and other sensory modalities are thought to play a vital role in developing and maintaining bodily awareness. How do blind people perceive their bodies, and what kind of compensatory neuroplasticity processes are involved? This thesis comprises a series of experiments focused on a profoundly understudied topic – the perception of one’s body following blindness. Study I shows that blind individuals are significantly better at perceiving their heartbeats than sighted individuals. The results indicate that blind individuals experience signals from inner organs differently than sighted individuals, which has implications for further research on emotional processing and bodily awareness. Study II provides a broader insight into tactile perception following blindness by studying discriminative and affective touch plasticity in blind and sighted groups. A key novel finding is changed pleasantness sensation due to affective touch, that is, slow, gentle, caress-like stroking of the skin, especially on the palm, in blind participants compared to sighted participants. The results have implications for understanding social and physical interactions in blind individuals. Study III re-examines a classic paradigm to study multisensory bodily awareness, the somatic rubber hand illusion, in a large sample of blind participants with a well-matched sighted control group. The results present strong evidence that blind individuals are “immune” to this illusion which suggests that they rely more on unisensory processing rather than multimodal integration of sensory signals, compared to sighted individuals. Study IV investigates the effect of short-term visual deprivation by a two-hour blindfolding procedure on the bodily senses of cardiac interoception, thermosensation, and discriminative touch in sighted participants. The results show no effect on these senses, which suggests that the changes observed in blind individuals on these sensory functions relate to their long-term lack of visual experience and associated brain plasticity changes. Finally, Study V uses structural magnetic resonance imaging to analyze cortical thickness in a group of blind individuals and a matched sighted control group and relate the cortical thickness measure to the behaviorally registered changes in cardiac interoceptive accuracy. The key finding is that blind individuals with thicker occipital cortices are better at sensing their heartbeats; this finding advances our understanding of the limits of cross-modal plasticity following blindness and suggests that the visual cortex supports the awareness of inner bodily sensations in blind individuals. Overall, this thesis is the first systematic characterization of differences and similarities between blind and sighted individuals in body perception and functioning of the bodily senses, opening a line of research with important links to mental health

Limits of cross-modal plasticity? Short-term visual deprivation does not enhance cardiac interoception, thermosensation, or tactile spatial acuity

In the present study, we investigated the effect of short-term visual deprivation on discriminative touch, cardiac interoception, and thermosensation by asking 64 healthy volunteers to perform four behavioral tasks. The experimental group contained 32 subjects who were blindfolded and kept in complete darkness for 110 minutes, while the control group consisted of 32 volunteers who were not blindfolded but were otherwise kept under identical experimental conditions. Both groups performed the required tasks three times: before and directly after deprivation (or control) and after an additional washout period of 40 minutes, in which all participants were exposed to normal light conditions. Our results showed that short- term visual deprivation had no effect on any of the senses tested. This finding suggests that short-term visual deprivation does not modulate basic bodily senses and extends this principle beyond tactile processing to the interoceptive modalities of cardiac and thermal sensations.Swedish Research Council, 2017-03135Marie Skłodowska-Curie Intra-European Individual Fellowship, 891175Accepte

The influence of short-term visual deprivation on the flexibility of body representation

Krótkotrwała deprywacja wzroku poprzez zasłonięcie oczu u osób zdrowych wpływa na ostrość dotyku i orientację w przestrzeni oraz, na poziomie neuronalnym, prowadzi do pobudzenia kory wzrokowej i kory motorycznej. Wpływ tego typu deprywacji na reprezentację własnego ciała nie został do tej pory zbadany. W niniejszej pracy przebadano dwie grupy 30 ochotników, wykorzystując podstawowy w badaniach percepcji ciała paradygmat – somatyczną wersję iluzji gumowej ręki. Przed rozpoczęciem procedury, grupie eksperymentalnej zasłonięto oczy na 120 minut, podczas gdy grupa kontrolna została poproszona o założenie przezroczystych okularów laboratoryjnych. Wyniki badania wskazują, że choć nie ma różnicy pomiędzy grupami w subiektywnym poczuciu iluzji, w grupie eksperymentalnej zaobserwowano istotnie większy dryf proprioceptywny, będący jednym z obiektywnych wskaźników iluzji. Wskazuje to, że krótkotrwała deprywacja sensoryczna poprzez zasłonięcie oczu może zwiększać elastyczność dynamicznej reprezentacji własnego ciała.Short-term visual deprivation by blindfolding influences tactile acuity and orientation in space and, on a neural level, leads to enhanced excitability of visual and motor cortices. However, to the best of our knowledge, the possible effects of short-term visual deprivation on body representation have not been examined. In the present study, we tested two groups of 30 healthy participants with the somatic rubber hand illusion, a well-established paradigm to probe the dynamic plasticity of body representation. Before the start of the procedure, the experimental group was blindfolded for 120 minutes, while the control group wore transparent goggles for the same amount of time. We found that although there was no difference in the subjective feeling of ownership of the rubber hand during the illusion, the blindfolded group showed a significantly larger recalibration of hand position sense towards the location of the rubber hand than the control group. This finding suggests that short-term visual deprivation boosts plasticity of body representation in terms of multisensory spatial recalibration of hand position sense

Limits of cross-modal plasticity? Short-term visual deprivation does not enhance cardiac interoception, thermosensation, or tactile spatial acuity

In the present study, we investigated the effect of short-term visual deprivation on discriminative touch, cardiac interoception, and thermosensation by asking 64 healthy volunteers to perform four behavioral tasks. The experimental group contained 32 subjects who were blindfolded and kept in complete darkness for 110 minutes, while the control group consisted of 32 volunteers who were not blindfolded but were otherwise kept under identical experimental conditions. Both groups performed the required tasks three times: before and directly after deprivation (or control) and after an additional washout period of 40 minutes, in which all participants were exposed to normal light conditions. Our results showed that short-term visual deprivation had no effect on any of the senses tested. This finding suggests that short-term visual deprivation does not modulate basic bodily senses and extends this principle beyond tactile processing to the interoceptive modalities of cardiac and thermal sensations

Are blind individuals immune to bodily illusions? Somatic rubber hand illusion in the blind revisited

Multisensory awareness of one’s own body relies on the integration of signals from various sensory modalities such as vision, touch, and proprioception. But how do blind individuals perceive their bodies without visual cues, and does the brain of a blind person integrate bodily senses differently from a sighted person? To address this question, we aimed to replicate the only two previous studies on this topic, which claimed that blind individuals do not experience the somatic rubber hand illusion, a bodily illusion triggered by the integration of correlated tactile and proprioceptive signals from the two hands. We used a larger sample size than the previous studies and added Bayesian analyses to examine statistical evidence in favor of the lack of an illusion effect. Moreover, we employed tests to investigate whether enhanced tactile acuity and cardiac interoceptive accuracy in blind individuals could also explain the weaker illusion. We tested 36 blind individuals and 36 age- and sex-matched sighted volunteers. The results show that blind individuals do not experience the somatic rubber hand illusion based on questionnaire ratings and behavioral measures that assessed changes in hand position sense toward the location of the rubber hand. This conclusion is supported by Bayesian evidence in favor of the null hypothesis. Tactile acuity was not correlated with illusion measures in either group, but cardiac interoceptive accuracy was negatively correlated with questionnaire ratings of illusion strength in the sighted group. The findings confirm that blind individuals do not experience the somatic rubber hand illusion, indicating that lack of visual experience leads to permanent changes in multisensory bodily perception. Taken together, this study suggests that changes in multisensory integration of tactile and proprioceptive signals, possibly combined with more accurate interoception, may explain why blind individuals appear “immune” to the nonvisual version of the rubber hand illusion

The perception of affective and discriminative touch in blind individuals

Enhanced tactile acuity in blindness is among the most widely reported results of neuroplasticity following prolonged visual deprivation. However, tactile submodalities other than discriminative touch are profoundly understudied in blind individuals. Here, we examined the influence of blindness on two tactile submodalities, affective and discriminative touch, the former being vital for social functioning and emotional processing. We tested 36 blind individuals and 36 age- and sex-matched sighted volunteers. In Experiment 1, we measured the perception of affective tactile signals by asking participants to rate the pleasantness of touch delivered on the palm (nonhairy skin, sparsely innervated with C tactile [CT] fibers) or the forearm (hairy skin, densely innervated with CT fibers) in a CT-optimal versus a CT-nonoptimal manner using a paradigm grounded in studies on tactile sensory neurophysiology. In Experiment 2, we implemented a classic task assessing discriminative touch abilities, the grating orientation task. We found that blind individuals rated the touch as more pleasant when delivered on the palm than on the forearm, while the opposite pattern was observed for sighted participants, who had a tendency to rate stimulation on the forearm as more pleasant than stimulation on the palm. We also replicated the previous findings showing enhanced discriminative tactile acuity in blind individuals. Taken together, our findings suggest that blind individuals experience affective and social touch differently than sighted individuals, with a relatively greater pleasantness perceived on the palm. These results provide a broader insight into somatosensory perception in blind individuals, for the first time taking into consideration the socioemotional aspect of touch