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

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ABSTRACT

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.

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The relationship between the salivary oxytocin concentration and subjective feeling of the rubber hand illusion (RHI). (A) Distributions of the salivary oxytocin concentration before the task and subjective feelings of RHI (Items 1, 2, and 3) in each block (1–4). Note that the participants who had higher concentrations of salivary oxytocin tended to feel stronger ownership of the rubber hand in the RHI (Item 3). Each data point indicates the data from the 15 participants. (B) Distributions of the salivary oxytocin concentration before the task and subjective feelings of RHI (Items 3) in blocks 2–4. Each data point indicates the averaged data of blocks 2–4 from 15 participants. (C) Changes in salivary oxytocin concentration before and after the task (n = 14). Note that oxytocin concentrations did not change after the occurrence of the RHI both in the Synchronous and Asynchronous conditions.
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Figure 2: The relationship between the salivary oxytocin concentration and subjective feeling of the rubber hand illusion (RHI). (A) Distributions of the salivary oxytocin concentration before the task and subjective feelings of RHI (Items 1, 2, and 3) in each block (1–4). Note that the participants who had higher concentrations of salivary oxytocin tended to feel stronger ownership of the rubber hand in the RHI (Item 3). Each data point indicates the data from the 15 participants. (B) Distributions of the salivary oxytocin concentration before the task and subjective feelings of RHI (Items 3) in blocks 2–4. Each data point indicates the averaged data of blocks 2–4 from 15 participants. (C) Changes in salivary oxytocin concentration before and after the task (n = 14). Note that oxytocin concentrations did not change after the occurrence of the RHI both in the Synchronous and Asynchronous conditions.

Mentions: In the present study, salivary oxytocin was measured before and after the behavioral tasks (Figure 1A). We compared the relationship between salivary oxytocin concentration (before the behavioral task in the Synchronous condition) and the subjective feeling of the RHI. The change in the illusory feeling attributed to the RHI was calculated by subtracting the response in the Asynchronous condition from the response scored in the Synchronous condition (“Sync–Async”). We found that the salivary oxytocin concentration was positively correlated with a change in the sensation of body ownership of the rubber hand (Item 3, N = 15) in Blocks 2–4 (r = 0.72, p = 0.0026 < 0.01, Power (1-β) = 0.9; r = 0.56, p = 0.028 < 0.05, Power (1-β) = 0.62; r = 0.57, p = 0.028 < 0.05, Power (1-β) = 0.64, respectively, Pearson product-moment correlation coefficient, Figure 2A, Table 2). When data from Blocks 2–4 were combined for better signal-to-noise ratio, strong correlation was observed (r = −0.77, p = 0.00087 < 0.001, Power (1-β) = 0.96, Figure 2B), and the correlation was still significant with combined data from Blocks 1–4 (r = 0.57, p = 0.028 < 0.05, Power (1-β) = 0.64). In addition, the salivary oxytocin concentration was also directly correlated with a score in the Synchronous condition (Item 3) in Blocks 2–4 (r = 0.76, p = 0.0010 < 0.01, Power (1-β) = 0.95; r = 0.75, p = 0.012 < 0.05, Power (1-β) = 0.94; r = 0.62, p = 0.014 < 0.05, Power (1-β) = 0.74, respectively). These results indicated that participants who had high concentrations of salivary oxytocin tended to feel a strong ownership of the rubber hand caused by the RHI. In contrast, no significant correlation between salivary oxytocin concentrations and other questions related to spatial changes in body representation (Items 1 and 2; Figure 2A, Table 2) or proprioceptive drift (Table 2) was observed. These data provide experimental support to our first hypothesis indicating that oxytocin enhanced plastic changes in body ownership during the RHI. In addition, no significant correlation was found between the salivary oxytocin concentration and change in the score of the control questions (Items 4–9; Table 2).


Salivary Oxytocin Concentration Associates with the Subjective Feeling of Body Ownership during the Rubber Hand Illusion
The relationship between the salivary oxytocin concentration and subjective feeling of the rubber hand illusion (RHI). (A) Distributions of the salivary oxytocin concentration before the task and subjective feelings of RHI (Items 1, 2, and 3) in each block (1–4). Note that the participants who had higher concentrations of salivary oxytocin tended to feel stronger ownership of the rubber hand in the RHI (Item 3). Each data point indicates the data from the 15 participants. (B) Distributions of the salivary oxytocin concentration before the task and subjective feelings of RHI (Items 3) in blocks 2–4. Each data point indicates the averaged data of blocks 2–4 from 15 participants. (C) Changes in salivary oxytocin concentration before and after the task (n = 14). Note that oxytocin concentrations did not change after the occurrence of the RHI both in the Synchronous and Asynchronous conditions.
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Related In: Results  -  Collection

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Figure 2: The relationship between the salivary oxytocin concentration and subjective feeling of the rubber hand illusion (RHI). (A) Distributions of the salivary oxytocin concentration before the task and subjective feelings of RHI (Items 1, 2, and 3) in each block (1–4). Note that the participants who had higher concentrations of salivary oxytocin tended to feel stronger ownership of the rubber hand in the RHI (Item 3). Each data point indicates the data from the 15 participants. (B) Distributions of the salivary oxytocin concentration before the task and subjective feelings of RHI (Items 3) in blocks 2–4. Each data point indicates the averaged data of blocks 2–4 from 15 participants. (C) Changes in salivary oxytocin concentration before and after the task (n = 14). Note that oxytocin concentrations did not change after the occurrence of the RHI both in the Synchronous and Asynchronous conditions.
Mentions: In the present study, salivary oxytocin was measured before and after the behavioral tasks (Figure 1A). We compared the relationship between salivary oxytocin concentration (before the behavioral task in the Synchronous condition) and the subjective feeling of the RHI. The change in the illusory feeling attributed to the RHI was calculated by subtracting the response in the Asynchronous condition from the response scored in the Synchronous condition (“Sync–Async”). We found that the salivary oxytocin concentration was positively correlated with a change in the sensation of body ownership of the rubber hand (Item 3, N = 15) in Blocks 2–4 (r = 0.72, p = 0.0026 < 0.01, Power (1-β) = 0.9; r = 0.56, p = 0.028 < 0.05, Power (1-β) = 0.62; r = 0.57, p = 0.028 < 0.05, Power (1-β) = 0.64, respectively, Pearson product-moment correlation coefficient, Figure 2A, Table 2). When data from Blocks 2–4 were combined for better signal-to-noise ratio, strong correlation was observed (r = −0.77, p = 0.00087 < 0.001, Power (1-β) = 0.96, Figure 2B), and the correlation was still significant with combined data from Blocks 1–4 (r = 0.57, p = 0.028 < 0.05, Power (1-β) = 0.64). In addition, the salivary oxytocin concentration was also directly correlated with a score in the Synchronous condition (Item 3) in Blocks 2–4 (r = 0.76, p = 0.0010 < 0.01, Power (1-β) = 0.95; r = 0.75, p = 0.012 < 0.05, Power (1-β) = 0.94; r = 0.62, p = 0.014 < 0.05, Power (1-β) = 0.74, respectively). These results indicated that participants who had high concentrations of salivary oxytocin tended to feel a strong ownership of the rubber hand caused by the RHI. In contrast, no significant correlation between salivary oxytocin concentrations and other questions related to spatial changes in body representation (Items 1 and 2; Figure 2A, Table 2) or proprioceptive drift (Table 2) was observed. These data provide experimental support to our first hypothesis indicating that oxytocin enhanced plastic changes in body ownership during the RHI. In addition, no significant correlation was found between the salivary oxytocin concentration and change in the score of the control questions (Items 4–9; Table 2).

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus