Konstantina Kilteni

Human ticklishness is one of the oldest yet unresolved scientific puzzles. As early as the time of Aristotle and Socrates, scholars have speculated on its origins and function, but fundamental questions remain. Is ticklishness culturally shared or specific? Does it follow a structured bodily topography, and how does it relate to other bodily sensations? Here we analysed data from three cultural groups (Chinese, Dutch and Greek) and reveal consistent behavioural patterns and social dynamics. We extracted a high-resolution bodily map of ticklishness and show that it generalizes across cultures and individuals, and is distinct from maps of touch sensitivity, pain and pleasure. When tested against predictions from five historical and contemporary theories, we show that no single theory can fully explain the ticklishness topography. Although ticklishness is stronger in rarely touched regions, supporting Darwin’s hypothesis, its topography relies on a psychophysiological mechanism that is more complex than previously assumed.

Motor control theories suggest that the brain uses forward models to predict self-generated tactile input during voluntary movements, thereby reducing the intensity of reafferent tactile sensations. When one's own body is the target, this phenomenon is called self-touch attenuation. Although self-touch attenuation is well documented, it remains unclear how prediction-related neural mechanisms drive attenuation before the self-touch input. We used magnetoencephalography to examine the neural correlates of self-touch prediction. Twenty-four human participants (12 females, 12 males) performed a self-touch, and two control tasks. In one control, they received externally generated touch without movement. In the other, the touch was triggered by the participant's movement, but the hands were spatially misaligned. This manipulation is known to weaken attenuation despite identical tactile input, movement, and task demands, because the sensorimotor context reduces prediction of touch at that body site. Self-touch evoked weaker somatosensory activity (M50 component) than both control conditions. A psychophysics task mirrored the pattern of neural attenuation, as the perception of self-touch was attenuated compared with the two control conditions. To isolate predictive neural mechanisms from general movement-related activity, we subtracted activity from corresponding stimulus-absent trials. Comparing self-touch with misaligned touch allowed us to refine the signal specific to predictive processing in self-touch and revealed greater prestimulus beta-band desynchronization and increased cerebellar-to-somatosensory connectivity before self-touch compared with misaligned touch. Our results provide the first evidence of predictive neural activity that shapes the sensory consequences of self-touch, offering insights into the mechanisms through which predictive models modulate somatosensory processing.

Disorders of consciousness (DoC) can result from severe acquired brain injuries disrupting arousal (wakefulness) and/or awareness (self and environment perception) (1,2). In coma, both arousal and ...

Processing of contaminants in odor mixtures is influenced by their categorization into food and nonfood categories. For example, we previously found that participants were more likely to perceive food odors as contaminated by nonfood odors than vice versa, and that this effect was robust to changes in explicit task instructions. However, due to the mixing of food and nonfood components, processing differences between categories were not captured by this task design and thus remain to be explored. In the current pre-registered study, we address this knowledge gap by determining the effects of attention on the perception of odor mixtures containing only food or nonfood components. Participants (N = 24) assessed the perceived dominance of a target odor within an odor mixture. Response times to all odors increased toward the dilution series’ midpoint and were faster for food odor compared to nonfood odor mixtures. Perceived target dominance increased linearly for nonfood targets but exhibited a sigmoidal shape with a steeper slope (smaller just-noticeable difference) for food targets. This implies that distinguishing 2 food odors was easier than distinguishing between 2 nonfood odors, likely due to definitions higher relevance of distinct object category boundaries subserving contamination avoidance. At the same time, contamination sensitivity might be lower for nonfoods, allowing for greater tolerance of deviations. Attention did not influence the perception of nonfood but did so for ambivalent food mixtures and when the target was completely absent.

Self‐touch is attenuated compared to external touch due to internal forward models predicting the somatosensory consequences of our movements. These self‐touch predictions are continuously updated during the movement using the available sensory input, resulting in a precise temporal tuning of somatosensory perception. However, the contributions of different sensory inputs, such as vision, to the predictions of the forward models and thus the resulting modulation of somatosensory perception remain unknown. In this pre‐registered study, participants discriminated forces applied to their left index or ring finger during a reaching movement of the right hand towards the left hand, performed both with and without visual input. When vision was available, somatosensory perception was gradually attenuated during the movement and peaked at the time of self‐touch, replicating our previous findings. Without visual input, this temporal tuning was reduced, as somatosensory perception was more uniformly, rather than gradually, attenuated throughout the movement. Our findings thus indicate that vision increases the precision of self‐touch predictions, thereby fine‐tuning the temporal modulation of somatosensory perception during movements to self‐touch.

Processing of contaminants in odour mixtures is influenced by their categorisation into food and non-food categories. For example, we previously found that participants were more likely to perceive food odours as contaminated by non-food odours than vice versa, and that this effect was robust to changes in explicit task instructions. However, due to the mixing of food and non-food components, processing differences between categories were not captured by this task design and thus remain to be explored. In the current pre-registered study, we address this knowledge gap by determining the effects of attention on the perception of odour mixtures containing only food or non-food components. Participants (N = 24) assessed the perceived dominance of a target odour within an odour mixture. Response times to all odours increased towards the dilution series’ midpoint and were faster for food odour compared to non-food odour mixtures. Perceived target dominance increased linearly for non-food targets but exhibited a sigmoidal shape with a steeper slope (smaller just-noticeable difference) for food targets. This implies that distinguishing two food odours was easier than distinguishing between two non-food odours, likely due to definitions higher relevance of distinct object category boundaries subserving contamination avoidance. At the same time, contamination sensitivity might be lower for non-foods, allowing for greater tolerance of deviations. Attention did not influence the perception of non-food but did so for ambivalent food mixtures and when the target was completely absent.

Perception and action are deeply intertwined processes that require the nervous system to distinguish between self-generated (reafferent) and externally generated (exafferent) sensory inputs. To maintain accurate perception during movement, the brain must attenuate predictable sensory consequences of its own actions while remaining sensitive to unexpected external events. Reafference attenuation is a temporally precise process that suppresses expected feedback, facilitating the detection of novel stimuli. This review examines reafference attenuation across species (rodents, nonhuman primates, and humans) and sensory systems (vestibular, auditory, and tactile). We also discuss sensory gating (or sensory suppression), a broader and often less selective mechanism that inhibits both self- and externally generated inputs. Although both mechanisms reduce sensory inflow during movement, they differ in function, specificity, and temporal dynamics, and despite growing insight into their underlying circuitry, important questions remain about their generality and implementation.

Motor control theories suggest that the brain uses forward models to predict self-generated tactile input during voluntary movements, thereby reducing the intensity of reafferent tactile sensations. When one’s own body is the target, this phenomenon is called self-touch attenuation. Although self-touch attenuation is well-documented, it remains unclear how prediction-related neural mechanisms drive attenuation before the self-touch input. We used magnetoencephalography (MEG) to examine the neural correlates of self-touch prediction. 24 human participants (12 female, 12 male) performed a self-touch, and two control tasks. In one control, they received externally generated touch without movement. In the other, the touch was triggered by the participant’s movement, but the hands were spatially misaligned. This manipulation is known to weaken attenuation despite identical tactile input, movement, and task demands, because the sensorimotor context reduces prediction of touch at that body site. Self-touch evoked weaker somatosensory activity (M50 component) than both control conditions. A psychophysics task mirrored the pattern of neural attenuation, as the perception of self-touch was attenuated compared to the two control conditions. To isolate predictive neural mechanisms from general movement-related activity, we subtracted activity from corresponding stimulus-absent trials. Comparing self-touch with misaligned touch allowed us to refine the signal specific to predictive processing in self-touch and revealed greater pre-stimulus beta-band desynchronization and increased cerebellar-to-somatosensory connectivity before self-touch compared to misaligned touch. Our results provide the first evidence of predictive neural activity that shapes the sensory consequences of self-touch, offering insights into the mechanisms through which predictive models modulate somatosensory processing. Significance statement: The brain is thought to predict and attenuate the sensory consequences of self-generated actions, but neural evidence for prediction before sensation has been limited. Using magnetoencephalography, we show that self-touch attenuation is preceded by beta-band desynchronization and increased directed connectivity from the cerebellum to the primary somatosensory cortex. These effects cannot be attributed to movement, as they were reduced in a control condition with similar motor output but lower congruence between the action and tactile consequence, suggesting spatially specific predictive processing. Our study provides the first neural evidence of cerebellar influence on cortical sensory areas before self-touch. These pre-stimulus effects support forward models of sensorimotor control and shed new light on how the brain anticipates and modulates upcoming sensory input.

Background: Individuals who engage in nonsuicidal self‐injury (NSSI) have a reduced pain sensitivity. Self‐induced pain is attenuated compared with externally induced pain, and this phenomenon, sensory attenuation, could partly explain the insensitivity to pain in individuals with NSSI. Methods: The objective was to assess sensory attenuation in women with NSSI compared to controls. In total, 81 women aged 18–35 years, mean age 23.4 (SD = 3.9), with NSSI ( n = 41) or controls ( n = 40) were recruited in this cross‐sectional study. Self‐induced and experimenter‐induced pressure pain thresholds were assessed. Correlation tests assessed possible associations between sensory attenuation and NSSI frequency, NSSI duration and conditioned pain modulation. Results: Across groups, the average self‐induced pressure pain was 164.8 kPa (SE = 25.2, 95% CI = 114.8–214.7) higher than the average experimenter‐induced pressure pain ( d = 0.66). On average, NSSI participants displayed 106.7 kPa (SE = 42.9, 95% CI = 21.7–191.8) higher pressure pain thresholds than controls ( d = 0.42), but there was no significant interaction effect for group (NSSI vs. controls) and condition (self‐induced vs. experimenter‐induced pain) ( p = 0.102). However, a greater number of NSSI participants than controls were identified as exhibiting sensory attenuation ( p = 0.022) when applying a threshold of ≥ 10% for sensory attenuation. Sensory attenuation correlated with conditioned pain modulation (tau = 0.17; p = 0.025), but not with NSSI frequency or duration. Conclusion: Sensory attenuation of self‐induced pressure was more prevalent in participants with NSSI than in controls, but there was no evidence that sensory attenuation was related to NSSI frequency or duration. The correlation between the sensory attenuation and conditioned pain modulation may be an indication of mutual anti‐nociceptive mechanisms. Significance Statement: Sensory attenuation of self‐induced pain was present in both participants with NSSI and controls, but a greater number of NSSI participants were identified as exhibiting sensory attenuation, applying a threshold of ≥ 10% for sensory attenuation. Sensory attenuation may facilitate NSSI behaviour because when pain is attenuated, the pain barrier for engaging in self‐harm will be reduced.