Rubber hand presentation modulates visuotactile interference effect especially in persons with high autistic traits

The relationship between the effect of hand visibility on visuotactile temporal resolution and autistic traits

Individuals with autism spectrum disorder (ASD) have atypical sensory processing, particularly when sensory stimuli are delivered from different modalities with a temporal lag of subseconds. Previous studies have suggested that individuals with ASD require a longer temporal lag to judge temporal orders of successive audiovisual stimuli than neurotypical individuals; however, it remains unclear whether a lower temporal resolution in the visuotactile domain is associated with an individual's autistic traits. In addition, a previous study demonstrated that visuotactile temporal resolution degraded when the participants saw a hand image on a display. In this study, we investigated whether the temporal resolution of the visuotactile stimuli degrades when the participant's own hand or rubber hands are visible, and whether the effect of the hand's visibility on the temporal resolution decreases according to an individual's autistic traits. We used the temporal order judgment (TOJ) of the vibrotactile stimulus delivered to the participant's index finger and an LED attached above their own hand or rubber hand. Our findings suggest that when participants could not see their hand, temporal order judgment tended to be coarser in participants with higher autistic traits. However, this tendency was not observed when they could see both their own or the rubber hands. Moreover, temporal resolution degraded when the participants could see their own hands. These results indicate that autistic traits influence the temporal resolution of visuotactile stimuli if they are delivered as external signals in TOJ.

Over-representation of fundamental decision variables in the prefrontal cortex underlies decision bias

The brain is organized into anatomically distinct structures consisting of a variety of projection neurons. While such evolutionarily conserved neural circuit organization underlies the innate ability of animals to swiftly adapt to environments, they can cause biased cognition and behavior. Although recent studies have begun to address the causal importance of projection-neuron types as distinct computational units, it remains unclear how projection types are functionally organized in encoding variables during cognitive tasks. This review focuses on the neural computation of decision making in the prefrontal cortex and discusses what decision variables are encoded by single neurons, neuronal populations, and projection type, alongside how specific projection types constrain decision making. We focus particularly on "over-representations" of distinct decision variables in the prefrontal cortex that reflect the biological and subjective significance of the variables for the decision makers. We suggest that task-specific over-representation in the prefrontal cortex involves the refinement of the given decision making, while generalized over-representation of fundamental decision variables is associated with suboptimal decision biases, including pathological ones such as those in patients with psychiatric disorders. Such over-representation of the fundamental decision variables in the prefrontal cortex appear to be tightly constrained by afferent and efferent connections that can be optogenetically intervened on. These ideas may provide critical insights into potential therapeutic targets for psychiatric disorders, including addiction and depression.

Atypical Effects of Visual Interference on Tactile Temporal Order Judgment in Individuals With Autism Spectrum Disorder

Visual distractors interfere with tactile temporal order judgment (TOJ) at moderately short stimulus onset asynchronies (SOAs) in typically developing participants. Presentation of a rubber hand in a forward direction to the participant's hand enhances this effect, while that in an inverted direction weakens the effect. Individuals with autism spectrum disorder (ASD) have atypical multisensory processing; however, effects of interferences on atypical multisensory processing in ASD remain unclear. In this study, we examined the effects of visual interference on tactile TOJ in individuals with ASD. Two successive tactile stimuli were delivered to the index and ring fingers of a participant's right hand in an opaque box. A rubber hand was placed on the box in a forward or inverted direction. Concurrently, visual stimuli provided by light-emitting diodes on the fingers of the rubber hand were delivered in a congruent or incongruent order. Participants were required to judge the temporal order of the tactile stimuli regardless of visual distractors. In the absence of a visual stimulus, participants with ASD tended to judge the simultaneous stimuli as the ring finger being stimulated first during tactile TOJ compared with typically developing (TD) controls, and congruent visual stimuli eliminated the bias. When incongruent visual stimuli were delivered, judgment was notably reversed in participants with ASD, regardless of the direction of the rubber hand. The findings demonstrate that there are considerable effects of visual interferences on tactile TOJ in individuals with ASD.

Salivary Oxytocin Concentration Associates with the Subjective Feeling of Body Ownership during the Rubber Hand Illusion

Oxytocin is a hormone of the posterior pituitary that promotes lactation, maternal bonding, and birth. Recent studies have shown that oxytocin may modulate social recognition in both sexes, and thus it may be related to empathy. Brain regions that are associated with social recognition and empathy (e.g., the insular cortex) are activated in the rubber hand illusion (RHI), which involves illusory ownership of a rubber hand caused by brush strokes applied synchronously to both a rubber hand and one of the participant's hand, which is hidden from view. It is intriguing to examine whether oxytocin modulates plastic changes in body representation, such as the changes occurring in the RHI. In the present study, we investigated the relationship between salivary oxytocin concentration and the feeling of rubber hand ownership. Brush strokes were applied synchronously or asynchronously to the participant's hand and a rubber hand on different days. Salivary oxytocin was measured before and after the behavioral tasks. We found that participants who had high concentrations of salivary oxytocin tended to feel strong ownership of the rubber hand. We also found that the participants with a high autism spectrum quotient (AQ) score who particularly felt difficulties in social skills and communications tended to feel weak rubber hand ownership. We observed that illusory body ownership was closely linked to social communications and a related neuroendocrine basis. The results of the present study suggest that an individual's salivary oxytocin concentration can predict the extent to which the individual experiences the RHI; furthermore, oxytocin might modulate the sensation of body ownership.