**3. Results**

Angles of the illusion were significantly decreased in situation 2 compared to situation 1 (Fig. 7, p < 0.05), while brain activity in the premotor area as assessed by effect size was reduced in situation 2. To confirm this finding, cerebral areas related to these channels were superimposed on MRI images and were identified as the right premotor area. (Fig. 8) On the other hand, there was a positive relationship, although not significant (p = 0.17), between a decrease in illusion angles and a reduction in activity in the right premotor area (r = 0.58).

Brain Activity and Movement Cognition:

blood flow.

within circle)

**4. Discussion** 

suppression of movement perception.

Vibratory Stimulation-Induced Illusions of Movements 109

Situation 1 Situation 2

Fig. 8. Comparison of cerebral cortical activities between situations 1 and 2.

Warm colors denote a relative increase in blood flow, while cold colors denote a relative decrease in

In situation 2, in the right premotor area there is a reduction in activity compared to situation 1. (Arrow

The present results clarified that the angle of illusion was decreased by placing a visible object within the range of illusory movement of the subject's own hand. It is therefore evident that visual sensation can modify illusory movement, indicating that the environment largely influences movement cognition. The effect size of the channels corresponding to the right premotor area were significantly reduced when vibratory stimulation was given in the presence of a visible object in comparison with absence of an object. In summary, the reduction in activity of the right premotor area was assumed to have diminished illusory movement as suggested by a positive correlation between intensities of the area activity and those of the illusion. That this correlation was not significant may have been because of the small subject population. It was thus clear that the activity of the premotor area of the right hemisphere influenced perception of movement and that the degree of activation of the right premotor area was involved in formation or

The right premotor area is the region responsible for bodily self-attribution as evidenced by Ehrsson et al.10) Evidence of the predominance of the right hemisphere in illusory perception of limb movement elicited by tendon vibration was also reported.8) Our present study added new information that a decline in activity in the premotor area suppressed illusory movements. Pinocchio's illusion11) helps explain this observation. When an illusory movement of elbow extension is provoked by vibratory stimulation with your nose being pinched, you feel as if your nose got longer. This phenomenon occurs to clear up a contradiction between illusory limb movements and constant input of tactile sensation from the nose. In this study, the subject should have touched an object due to illusory movements if it had existed within the illusory angle of the subject's own hand. Our results suggested that the degree of illusory movements was lowered due to lack of tactile sensation and that

From these results it was clarified that movement perception based on activity of muscle spindles was easily modified by a change in visual information even though the intensity of

the right premotor area might be involved in variability of illusory movements.

Channels were grouped into 5 regions and effect sizes from each region were averaged.

Fig. 6. Schema of regions of interest analysis

#### \* P<0.05

Situation 1: No object is presented, Situation 2: An object is presented. There is a significant reduction of flexion angles in situation 2 compared to situation 1. In other words,

Fig. 7. Differences in angles of hand joint flexion between Situations 1 and 2

object presentation reduces the degree of illusory hand joint flexion.

Warm colors denote a relative increase in blood flow, while cold colors denote a relative decrease in blood flow.

In situation 2, in the right premotor area there is a reduction in activity compared to situation 1. (Arrow within circle)

Fig. 8. Comparison of cerebral cortical activities between situations 1 and 2.
