# Bioelectrical Signals for the Diagnosis and Therapy of Functional Gastrointestinal Disorders
## 3 Stomach
### Diagnostics  
Bioelectrical events such as SWs have a regulatory role in gastric motility. Therefore, the quantification of SWs has potential for the assessment of FGIDs. The first SW recordings were performed by [PERSON] [58], and until the 1990s, a limited number of electrodes were employed to measure SWs from the gastric serosa [59; 60]. These low-resolution techniques revealed the temporal features of the SW activity and reported that SWs initiate and propagate at a frequency of approximately 3 cycles per minute (cpm) (see Figure 2a). However, they lacked spatial detail and their quantification was primarily limited to frequency-based analysis. As such, they were also unable to determine mechanisms underlying the initiation, maintenance or termination of SW patterns accurately but served as a strong foundation for our current understanding of GI electrophysiology [61]. The introduction of high-resolution SW mapping techniques has overcome such challenges [62]. High-resolution mapping in humans has shown that SWs have varying properties in different regions of the stomach [63; 64]. Normal SW activity originates from a pacemaker region on the greater curvature in the upper corpus. Then, the SWs organize into bands and propagate towards and terminate at the pylorus. Abnormal SW activity has been implicated as a disease mechanism in several functional gastric disorders [13]. More importantly, spatially complex SW initiation and conduction patterns that occur within the normal frequency range and cannot be identified using traditional frequency analysis techniques have been linked with gastroparesi and chronic unexplained nausea and vomiting [65; 66]. In addition, ICC loss and network degradation have been observed in patients with gastroparesi [67; 68]. Therefore, monitoring SW activity is a potential method for diagnosing FGIDs. Even though high-resolution mapping provides the most accurate SW measures, the invasiveness limits its clinical utility. Therefore, laparoscopic and mucosal mapping approaches have been used to minimize invasiveness. [PERSON] et al. presented the first laparoscopic extracellular SW recordings from the stomach and small bowel using pairs of stainless-steel electrodes [69]. In the last decade, several approaches were investigated to exploit multielectrode arrays in laparoscopic SW mapping [70; 71]. Endoscopic approaches were also investigated as a minimally invasive strategy to measure SWs from the mucosal surface of the stomach [72; 73]. Recently, the ability to monitor mucosal SW activity over extended periods has been reported [74]. Figure 2: Spatial variation of dominant slow wave (SW) frequencies in the stomach, small intestine, and colon in healthy humans. (**a**) The SW frequency is approximately 3 cpm (red) and uniform across the stomach. (**b**) The small intestine has temporally and spatially dynamic SW patterns where the frequency decreases in a stepwise fashion aborally from approximately 12 cpm (red) in the duodenum to 8 cpm (blue) in the distal ileum. (**c**) Two types of SW rhythms coexist throughout the colon. In the proximal and distal colon, low-frequency activity (2–9 cpm, blue) dominates, while high-frequency activity (9–13 cpm, red) is more prevalent between these regions. The relative size of these zones is variable between subjects. Reliable methods for non-invasive and possibly long-term recordings of SW activity such as body surface electrogastrography (EGG) would be a significant advance for clinical diagnosis. EGG is a technique to measure gastric myoelectrical activity using electrodes located on the body surface. Several studies have used EGG to assess FGIDs such as gastroparesis, functional dyspepsia and chronic nausea, and observed abnormal EGG patterns [75,76]. Recently, high-resolution electrodes have been employed in EGG measurements to assess the signatures of gastric disorders. The spatial distribution of the electrodes has enabled the characterization of the spatio-temporal patterns of the gastric electrical activity in addition to its frequency dynamics.