### Literature Review of AI, Acupuncture and EEG
#### 1.3.2 EEG Studies on Acupuncture and Related Modalities  
Using the search string 'EEG AND (acupuncture OR transcutaneous) NOT (\"vagal stimulation\" OR \"vagus nerve stimulation\"), about 500 studies were identified in PubMed. Of these, around 147, published between 1986 and 2022, were easily retrieved and could be examined in depth. Here, we consider those on steady-state EEG rather than evoked potentials. Of these, 56 (around 38%) were from China, 15 from Korea, 13 from the US, 11 from Japan and 10 from Taiwan. Other countries were represented by fewer than 10 studies each. Of the Chinese studies, 25 (more than 44%), or almost half, were from Hebei University of Technology (Tianjin University).  
Most of these EEG studies were on manual acupuncture, and it should be remembered that 'TEAS is different from inserting electroacupuncture in many ways, and the results from these studies may not apply to acupuncture' [20]. In the acupuncture-related studies, the points most commonly used -- as noted in a 2018 systematic review of 19 EEG acupuncture studies [21] -- were ST36 (_zusanli_,,, Zusanli_), on the leg below the knee and lateral to the anterior crest of the tibia; L14 (_hegu_,,, Hegii), located in the area covered by the superficial branch of the radial nerve, and close to the radial artery or first dorsal metacarpal artery, i.e., on the back of the hand between the first and second metacarpals; and P6 (_neiguan_,, Neiguan), on the anterior surface of the forearm, proximal to the wrist crease between the palmaris longus and flexor carpi radialis tendons.  
Methods of analysing changes in EEG were varied. Measures based on EEG power occurred in similar numbers of studies published before and after 2013, the median year of publication for the 147 studies located, as did nonlinear entropy and complexity measures. Only one study on cordance was located. Functional connectivity measures based on a graph or network theory -- i.e., quantifying relationships between EEG at different electrodes [22] -- were found in only one study before 2013, but in 13 of the 72 studies published since then.  
Of the Tianjin studies located, 14 were on manual acupuncture, 10 on non-invasive magnetic stimulation (TMS--transcranial magnetic stimulation), one on moxibustion and one on 100 Hz microcurrent TEAS. Half the Tianjin acupuncture studies, published be tween 2010 and 2021, investigated the effects of different frequencies of needle-twirling at ST36 in EEG. Participants were lying down with their eyes closed in a darkened room. Three different frequencies were used in the same session, with between 4 and 10 min rests between them, depending on the study. In contrast, only one upper limb TENS study, a BSc thesis from Holland, investigated the effects of stimulation frequency on EEG and did not use low-frequency stimulation.  
As yet, there are only two studies in PubMed on artificial intelligence (whether machine learning or deep learning), EEG and acupuncture or transcutaneous stimulation (TENS or TEAS), with one of these being from Tianjin, as mentioned above [11]. Seven studies were also located in a separate PubMed search for 'acupuncture' AND 'wavelet' AND 'EEG'. Of these, four were on wavelet packet decomposition (WPD). Three of them were from Tianjin [23; 24; 25], and one from Shenyang [26]. A further study investigating the effects of 20-100 Hz transcutaneous brachial stimulation on EEG wavelet entropy was noted [27], but it did not involve AI or explore the effects of different stimulation frequencies. Thus, _no prior AI research appears to have been conducted on the effects of different frequencies of stimulation (whether EA or TEAS) on EEG._