**2. Methods**

### **2.1 Subjects**

Eight healthy adults in their 20s were initially examined for the intensity of the sensation of illusory movement after vibratory stimulation of the hand extensor tendon using the vibratory stimulation apparatus described below. Intensity was graded on a 5-stage scale. The 7 individuals who were assessed as having scale 4 (strong illusory sensation) or greater were studied. These 7 subjects were observed for brain activity when they experienced illusory sensations and were found to have increased blood flow in the area that responded to illusory movement sensation.6) They were therefore considered eligible for this study. According to the Helsinki Declaration, they were given an explanation about the purpose of this study before providing written informed consent.

### **2.2 Vibratory stimulation apparatus**

We used the SL-0105 LP (Asahifactory Corp., Tokyo) (Fig. 2) for vibratory stimulation under conditions of frequency of 80 Hz and intensity of 0.2 – 0.3, which was reported to most

and of the object moving in the same direction is felt. When an object is felt to move in an illusion, the left hemisphere is predominantly activated and regions of interest are the lobule

However, when an object is placed within the angle of a self-experienced illusion without the object being grasped, it remains to be clarified how much such visual information influences the degree of illusory movement and how the brain is activated. This chapter reports such influences as well as brain activity **as** explored by functional near-infrared

Eight healthy adults in their 20s were initially examined for the intensity of the sensation of illusory movement after vibratory stimulation of the hand extensor tendon using the vibratory stimulation apparatus described below. Intensity was graded on a 5-stage scale. The 7 individuals who were assessed as having scale 4 (strong illusory sensation) or greater were studied. These 7 subjects were observed for brain activity when they experienced illusory sensations and were found to have increased blood flow in the area that responded to illusory movement sensation.6) They were therefore considered eligible for this study. According to the Helsinki Declaration, they were given an explanation about the purpose of

We used the SL-0105 LP (Asahifactory Corp., Tokyo) (Fig. 2) for vibratory stimulation under conditions of frequency of 80 Hz and intensity of 0.2 – 0.3, which was reported to most

Fig. 1. Schema of tendon stimulation-induced illusory movement

of the inferior parietal lobe and Brodmann's area 44/45.6-8)

this study before providing written informed consent.

**2.2 Vibratory stimulation apparatus** 

spectroscopy (fNIRS).

**2. Methods 2.1 Subjects** 

a) Apparatus is in contact with the hand extensor tendon to elicit an illusion of hand joint flexion. (Situation 1)

b) Illustration of illusory movement.

Fig. 2. Application of vibratory stimulus

efficiently excite illusions by an earlier study.4) There were two experimental situations. In situation 1, vibratory stimulation was imposed to the hand extensor tendon without placing an object near the subject; In situation 2, stimulation was similarly imposed with an object (umbrella) standing upright within range of illusory flexion. (Fig. 3) In either situation, the skin near the tendon was stimulated, which served as a control. The purpose of this stimulation was to acquire data on brain activity that was elicited when skin irritation receptors (Meissner corpuscles, Pacinian corpuscles, etc.) were excited that could be subtracted from data acquired by tendon stimulation so that pure illusory brain activity could be calculated.

#### **2.3 Protocol of tasks**

A task to create an illusion for a period of more than 20 seconds was imposed between two 10-second resting times. This session was uninterruptedly repeated under each situation. The illusory flexion angle was estimated as follows. After accomplishment of a task, a

Brain Activity and Movement Cognition:

Vibratory Stimulation-Induced Illusions of Movements 107

 A B red circle: emission probe blue circle: detection probe

Emission probe #7 was placed at the Cz (panel A) as defined by the International 10-20 method so that

central sulcus

levels of oxy-Hb acquired over the first 5 seconds were discarded and levels obtained over another 5 seconds were subjected to analysis during both tasks and resting times. Furthermore, the issue of optical path length was solved by calculation of effect sizes (=[(an arithmetic mean value of oxy-Hb levels at a task ) – (that at a resting time)]/standard deviation at a resting time).9) In addition, effect sizes were separately averaged for each region of interest. Specifically they were analyzed as follows: ch 1, 2, 5, 6, 10, and 11 representing the right parietal lobe; ch 3, 4, 8, 9, 12, and 13, the left parietal lobe; ch 14 -27, bilateral sensorimotor areas; ch 28, 29, 32, 33, 37, 38, 41, 46, and 47, the right premotor area;

Differences in brain activity between situations 1 and 2 were tested with Wilcoxon matchedpairs signed-ranks test. Angles of illusions were analyzed by the t-test. Pearson's correlation coefficients were calculated to examine relations between differences in the angles of illusions between situations 1 and 2 and similar differences in the brain activity. Level of

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).

white band: ch

Fig. 5. Schematic arrangement of emission and detection probes.

and ch 30, 31, 35, 36, 44, 45, 48, and 49, the left premotor area. (Fig. 6)

measurement sites were the same in all subjects (panel B).

anterior

longitudinal cerebral fissure

posterior

right left

significance was set as p < 0.05.

**3. Results** 

subject was requested to reenact with an actual motion the illusory limb movement and the flexion angle was measured with an electric geniometer (SG150, Biometrics, Phoenix).

#### **2.4 Measurement by fNIRS**

Cerebral blood flow was measured using fNIRS FOIRE-3000 (Shimazu Co., Kyoto). (Fig. 4) Probes were fixed using a flexible holder to cover the entire head, which was placed on the surface of the scalp covering the bilateral frontal and parietal lobes. (Fig. 4) The distance between the pair of emission and detector probes was 3.0 cm and the pair was set as a channel (ch). The Cz of the International 10-20 method for EEG was set at the point where a line drawn between the bilateral external auditory pores and a perpendicular line from the nose intersect. Emission probe #7 was placed at the Cz to allow measurement sites be shared equally by all the subjects. Fifteen emission probes (E) and detection probes (D), respectively, were placed in a 5X6 arrangement in order starting from the left forehead. It total, 49 channels were provided. (Fig. 5) To prevent the hair from protruding, fibers (multicomponent glass band fibers) were set **through the hair to a fiber holder to ensure that their tips contacted the scalp.** 

Emission and detector probes are placed at a distance of 3 cm from each other and each pair of probes works as a channel.

Fig. 4. Subject wearing flexible probe holder covering the entire scalp.

#### **2.5 Data analysis**

Brain active sites were identified using 3 SPACE FASTRAK (POLHEMU Co., Vermont) and were superimposed on images obtained by magnetic resonance imaging (MRI) using FUSION imaging software (Shimazu, Co., Kyoto).

Oxidized hemoglobin (oxy-Hb) levels at tendon stimulation acquired from 3 continuous task sessions were averaged to get an arithmetic mean from which another arithmetic mean, that which was similarly acquired as the skin was stimulated, was subtracted. Final values were statistically analyzed. Since it is known that there is a time lag of several seconds between the onset of neural activity and change in cerebral blood flow as detected by fNIRS,

subject was requested to reenact with an actual motion the illusory limb movement and the flexion angle was measured with an electric geniometer (SG150, Biometrics, Phoenix).

Cerebral blood flow was measured using fNIRS FOIRE-3000 (Shimazu Co., Kyoto). (Fig. 4) Probes were fixed using a flexible holder to cover the entire head, which was placed on the surface of the scalp covering the bilateral frontal and parietal lobes. (Fig. 4) The distance between the pair of emission and detector probes was 3.0 cm and the pair was set as a channel (ch). The Cz of the International 10-20 method for EEG was set at the point where a line drawn between the bilateral external auditory pores and a perpendicular line from the nose intersect. Emission probe #7 was placed at the Cz to allow measurement sites be shared equally by all the subjects. Fifteen emission probes (E) and detection probes (D), respectively, were placed in a 5X6 arrangement in order starting from the left forehead. It total, 49 channels were provided. (Fig. 5) To prevent the hair from protruding, fibers (multicomponent glass band fibers) were set **through the hair to a fiber holder to ensure that** 

Emission and detector probes are placed at a distance of 3 cm from each other and each pair of probes

Brain active sites were identified using 3 SPACE FASTRAK (POLHEMU Co., Vermont) and were superimposed on images obtained by magnetic resonance imaging (MRI) using

Oxidized hemoglobin (oxy-Hb) levels at tendon stimulation acquired from 3 continuous task sessions were averaged to get an arithmetic mean from which another arithmetic mean, that which was similarly acquired as the skin was stimulated, was subtracted. Final values were statistically analyzed. Since it is known that there is a time lag of several seconds between the onset of neural activity and change in cerebral blood flow as detected by fNIRS,

Fig. 4. Subject wearing flexible probe holder covering the entire scalp.

FUSION imaging software (Shimazu, Co., Kyoto).

**2.4 Measurement by fNIRS** 

**their tips contacted the scalp.** 

works as a channel.

**2.5 Data analysis** 

Emission probe #7 was placed at the Cz (panel A) as defined by the International 10-20 method so that measurement sites were the same in all subjects (panel B).

Fig. 5. Schematic arrangement of emission and detection probes.

white band: ch

levels of oxy-Hb acquired over the first 5 seconds were discarded and levels obtained over another 5 seconds were subjected to analysis during both tasks and resting times. Furthermore, the issue of optical path length was solved by calculation of effect sizes (=[(an arithmetic mean value of oxy-Hb levels at a task ) – (that at a resting time)]/standard deviation at a resting time).9) In addition, effect sizes were separately averaged for each region of interest. Specifically they were analyzed as follows: ch 1, 2, 5, 6, 10, and 11 representing the right parietal lobe; ch 3, 4, 8, 9, 12, and 13, the left parietal lobe; ch 14 -27, bilateral sensorimotor areas; ch 28, 29, 32, 33, 37, 38, 41, 46, and 47, the right premotor area; and ch 30, 31, 35, 36, 44, 45, 48, and 49, the left premotor area. (Fig. 6)

Differences in brain activity between situations 1 and 2 were tested with Wilcoxon matchedpairs signed-ranks test. Angles of illusions were analyzed by the t-test. Pearson's correlation coefficients were calculated to examine relations between differences in the angles of illusions between situations 1 and 2 and similar differences in the brain activity. Level of significance was set as p < 0.05.
