3. Results
168 [7, 10–176] original articles were included in this study.
Most of the studies were conducted in China (80 studies) [10, 11, 13, 14, 16, 18–24, 26, 27, 29–31, 33–36, 43–46, 48, 51, 53, 54, 56, 58–66, 68–70, 72–75, 77, 78, 83, 84, 86, 87, 89, 90, 93, 95, 97, 99–101, 104, 111, 113, 115, 123, 137, 138, 142, 144–147, 154, 159, 161–166] and in USA (40 studies) [15, 28, 37, 38, 42, 57, 70, 71, 76, 80, 88, 91, 94, 96, 105–107, 118–120, 124–127, 129–131, 133–136, 140, 141, 148, 151, 152, 155, 156, 158, 174]. The investigators in Korea (16 studies) [7, 47, 49, 52, 55, 82, 85, 98, 102, 109, 112, 114, 116, 117, 122, 153], Taiwan (6 studies) [79, 110, 128, 170, 171, 175], Austria (6 studies) [132, 139, 150, 160, 168, 176], Germany (5 studies) [32, 50, 157, 167, 169], Australia (4 studies) [40, 41, 92, 121], Japan (4 studies) [39, 108, 149, 173], UK (4 studies) [17, 67, 81, 103], Italy (2 studies) [25, 172], and Denmark (1 study) [143] also published articles on acupuncture-neuroimaging (Figure 1). 60 studies [16, 19, 23, 25, 26, 37, 38, 42, 45, 46, 55, 56, 60, 62, 65, 67, 70–72, 75, 78, 81, 87, 88, 90, 93, 97, 100, 101, 104, 106, 107, 110, 111, 113–115, 117–121, 123, 126–129, 132, 134, 137, 142, 145–147, 150, 157, 160, 162, 168, 175] were performed with the cooperation of more than two countries.

3.1. Sample Size
The average sample size of these studies was 15 participants per group. For the studies performed on patients, the average sample size was 16 participants per group, while the maximal and minimal sample sizes per group were 55 participants and 1 participant, respectively. For those performed on healthy subjects, the average sample size was 14 per group, and the maximal and minimal sample sizes per group were 48 participants and 1 participant, respectively.

3.2. The Status of Participants

3.2.1. Classification of Participants
122 studies [7, 11–13, 15–17, 24, 25, 30–33, 35, 36, 39, 41–45, 50, 53–57, 63, 64, 66–70, 72–76, 78–83, 85–100, 102–104, 106, 107, 109–111, 113–130, 132, 135, 136, 140, 143, 144, 147–176] were performed on healthy subjects. 25 studies were [10, 26–29, 34, 38, 49, 51, 58–60, 62, 65, 71, 84, 101, 105, 108, 112, 134, 137, 139, 142, 145] performed on patients. 21 studies [14, 18–23, 37, 40, 46–48, 52, 61, 77, 131, 133, 138, 141, 146, 165] recruited both healthy subjects and patients. 25 kinds of diseases were involved in these studies (Table 1). 19 studies [10, 14, 18, 19, 29, 34, 35, 40, 46, 51, 52, 59, 62, 65, 77, 84, 112, 134, 146] classified the subtypes of diseases.

3.2.2. Age
100 studies [7, 10, 16–19, 23, 24, 26, 27, 30, 34, 35, 39–42, 44–48, 51–54, 57, 59, 60, 62, 63, 65, 69–74, 76, 77, 80–82, 84, 85, 87, 89, 92, 97, 98, 101–103, 105, 107–109, 112, 114, 116, 117, 120–122, 124, 125, 129, 131–135, 137, 139, 141–145, 148–153, 157, 158, 160, 162, 164, 166–168, 171–176] described the age range of participants. For the healthy subjects, the average age range was 18.3 years old, and the maximal age range was 62, while the minimal age range was 3. For the patients, the average age range was 29 years old, and the maximal age range was 57, while the minimal age range was 6. Taking studies on the stroke for instance, the maximal age range of the stroke patients was 52, while the minimal age range was 7. Furthermore, 66 studies [11, 13–15, 20–22, 25, 28, 29, 31–33, 36–38, 43, 49, 50, 55, 56, 58, 61, 64, 66–68, 75, 78, 79, 83, 86, 88, 90, 91, 93, 95, 96, 99, 100, 104, 106, 110, 111, 113, 115, 118, 119, 123, 126–128, 130, 136, 138, 140, 146, 147, 154–156, 159, 161, 163, 169, 176] described the average age of participants. Three studies [94, 163, 170] did not mention the age of participants.

3.2.3. Gender
159 studies [7, 10–26, 28–79, 81–93, 95–114, 116–123, 125–131, 133–151, 153–169, 172–176] described the gender of the participants (56.7% male and 43.3% female). Nine studies [27, 80, 94, 115, 124, 132, 152, 170, 171] did not mention the gender of the participants.

3.2.4. Race and Handedness
14 studies [66, 75, 87, 90, 99, 105, 115, 126, 135, 148, 151, 164, 167, 174] described and restricted the race of participants. 136 [10–24, 26, 28, 30–36, 39–56, 58, 59, 61–80, 83–87, 89–93, 95, 96, 98–100, 103–107, 109–111, 113–115, 117–131, 133, 135–138, 140–142, 144, 146–149, 151–157, 159, 162–164, 166, 168, 169, 171, 173–175] studies asked for the right-hand participants in inclusion criteria.

3.2.5. Emotional State
The psychological assessment on the participants was performed in 4 studies [21, 31, 46, 92, 93]. The self-rating depression scale (SDS) and the self-rating anxiety scale (SAS) were used in 2 studies [31, 46]. The Beck Depression Inventory (BDI) [92] and the State Trait Anxiety Inventory (STAI) [93] were used in 1 study, respectively. Nine studies [19–22, 24, 65, 76, 92, 146] have excluded the participants with claustrophobia.

3.2.6. Accompanying Symptoms
38 studies [11, 13, 15, 21, 31, 36, 42, 43, 46, 54, 57, 64, 65, 68, 73, 76, 78, 81, 87, 93, 100, 102, 104, 106, 110–121, 123, 128, 133, 135, 141, 148, 151, 153, 156, 158, 165, 174] excluded the participants with head trauma, and some studies [24, 46, 54, 73, 100, 121, 122] excluded the participants suffering from pain (including headache and dysmenorrhea).

3.2.7. Acupuncture Experience
81 articles [13–16, 18, 22, 24, 26, 28, 29, 31, 33–35, 37, 38, 42, 51, 54–59, 63, 64, 67, 68, 70, 71, 73, 75, 78, 83, 85–87, 89, 90, 92, 93, 95, 96, 99, 101, 103–106, 108, 111, 113–115, 117–121, 123, 127, 130, 135, 138, 140, 144, 147, 148, 151–153, 156–158, 162, 166–169, 174] described the acupuncture experience of participants. Among these articles, 73 articles [12–16, 18, 22, 28, 29, 31, 33–35, 37, 38, 42, 51, 55, 57–59, 63, 64, 67, 68, 70, 71, 73, 75, 78, 83, 85–87, 89, 90, 93, 95, 96, 99, 101, 103–106, 108, 111, 113–115, 117–121, 123, 127, 130, 135, 138, 140, 144, 147, 148, 151–153, 157, 158, 166–169] described the participants as acupuncture naive.

3.3. Neuroimaging Technology
137 studies [7, 11, 12, 14–26, 28, 29, 31–42, 44–50, 52, 53, 55–61, 63, 64, 66, 68–79, 84–87, 89–101, 103, 104, 106, 107, 109–115, 117–120, 122, 123, 125–129, 131–136, 138–141, 144, 146–159, 161, 162, 164, 166–168, 170, 171, 173–175] used fMRI (82.14%) to investigate the cerebral responses to acupuncture stimulation. Six studies [43, 80, 88, 116, 130, 160] used the combination of two imaging technologies. The application of the techniques in acupuncture-neuroimaging studies was shown in Figure 2.

3.4. Acupuncture Intervention

3.4.1. Method of Intervention
111 studies [7, 10, 12–14, 16–26, 28, 29, 31–34, 36, 39, 42, 43, 46–59, 61, 63, 64, 66–68, 75, 78, 82, 83, 85–88, 90, 91, 93–95, 97–100, 102–106, 108–114, 125–129, 132, 135–139, 142, 144, 145, 148, 149, 151, 153, 154, 156, 157, 163–165, 167, 172, 174–176] chose manual acupuncture as intervention method. 32 studies [27, 37, 38, 44, 60, 62, 65, 69, 70, 72, 76, 77, 80, 84, 89, 96, 101, 107, 115–117, 124, 140, 146, 152, 159, 162, 166, 169–171, 173] chose electroacupuncture as intervention method. Besides, the transcutaneous electric acupoint stimulation was performed in 6 studies [45, 73, 74, 81, 141, 143], the laser acupuncture in 6 studies [40, 79, 92, 150, 160, 168], heat stimulation on acupoints in 2 studies [147, 155], and the magnetic stimulation on acupoints in 1 study [30]. There were 10 studies [11, 15, 35, 41, 71, 131, 133, 134, 158, 161] using at least two types of acupuncture methods (Figure 3).

3.4.2. Manipulation Procedure
134 articles [10–20, 22, 24, 26, 27, 29, 30, 34–39, 41, 42, 46–52, 54–70, 72, 73, 75–130, 132, 133, 135–138, 142, 144–146, 148, 151–154, 156–158, 163, 167–170, 172, 174–176] have described the manipulation procedure of acupuncture.

3.4.3. Deqi (Needle Sensation)
82 studies [10, 15, 16, 22, 23, 26, 28, 29, 34, 35, 37, 38, 41–47, 50, 54, 56, 57, 64, 68, 69, 72, 73, 75–77, 80, 87, 89–91, 93–96, 98–101, 103, 105–111, 114, 115, 117, 118, 120–124, 127, 130, 133, 135–138, 140, 144, 146, 148, 153, 157, 158, 166–168, 172, 174–176] required Deqi (needle sensation) during acupuncture stimulation.
56 studies [10, 14–18, 28, 35, 38, 42, 43, 50, 53, 55, 57, 58, 61, 64, 66, 68, 69, 71, 73, 75–77, 87, 89–91, 93–96, 99–101, 103, 104, 106–111, 115, 117, 120, 124, 127–130, 140, 166, 169] have evaluated needle sensation after acupuncture stimulation. The 10-point Visual Analogue Scale (VAS), the Massachusetts General Hospital Acupuncture Sensation Scale (MASS), the Subject Acupuncture Sensation Scale (SASS), the 6-point Likert scale, the Park questionnaire, the Psychophysical Rating of Needling Sensation, and the Needle Sensation Questionnaire (NSQ) were used to evaluate the needle sensation (Figure 4).

3.4.4. Qualification of Acupuncturists
99 articles [12, 14–19, 22–24, 26, 28, 29, 31–42, 44, 46–50, 52, 54–61, 63, 64, 66, 67, 69, 71, 72, 75, 78, 80, 82–84, 86, 87, 89–91, 93–98, 100–104, 106, 108–112, 114–117, 119–124, 126–129, 133, 135, 139, 140, 142, 144, 150, 158, 166, 174] have mentioned the qualification of acupuncturists.

3.5. The Ethical Review
139 studies [10–18, 20–29, 31–36, 38–45, 47–58, 60, 63–79, 81–86, 88, 90–93, 96–107, 109–115, 117–121, 123–125, 127, 128, 130–133, 135, 136, 138–148, 150–156, 158–162, 164, 166–168, 172, 174, 175] have mentioned the ethical review in the study.