# Bioelectrical Signals for the Diagnosis and Therapy of Functional Gastrointestinal Disorders
## 5 Large Intestine
### Diagnostics  
Bioelectrical measurements to assess the functionality of the large intestine were first used more than 50 years ago [122]. Several techniques, such as serosal, intraluminal, and cutaneous electrical measurements, have since been utilized. However, SW activity within the colon is less well-defined and more variable compared to the stomach and intestine which has led to conflicting reports [123]. Moreover, the temporal and spatial profiles of colonic electrical activity have shown to be variable between people [124]. In general, two types of SW rhythms coexist throughout the colon: (i) a high-frequency activity with low amplitude (9-13 cpm) and (ii) a low-frequency activity with high amplitude (2-9 cpm) [123; 124; 125]. The low-frequency activity was more dominant in the proximal and distal colon, while the high-frequency activity was more dominant between these zones (see Figure 2c). The extent of these dominant zones was reported to be highly variable between subjects [124].  
The first non-invasive measurements of colonic SW also known as electrocolonography (EColG) was reported by [PERSON] et al. in 1975 [125]. [PERSON] et al. performed transcutaneous electrical recording on the patients who underwent osteotomy and reported that the power peaks between 3.5 and 7.5 cpm were observed before osteotomy but were not present after [126]. More recently, high-resolution cutaneous electrodes were introduced to analyze changes in colon motor activity in humans during a meal-response study [127]. In the study, a 32-channel electrode array was utilized and roughly 3 h recordings with pre- and post-meal epochs were performed. A SW activity with a dominant frequency of 4 cpm was reported in the sigmoid colon region in agreement with earlier invasive studies.  
Several studies have attempted to identify the relationship between FBDs and underlying SW activity using myoelectrical recordings. A study performed on patients diagnosed with IBS reported that the low-frequency band of SW was recorded for a greater proportion of time in both the rectum and rectosigmoid compared to normal subjects [128]. A subsequent study showed that the frequency of colonic contractions was closely associated with the underlying SW frequency [129]. However, no differences were observed in the relationship between contractions and SW frequency between IBS and control groups. On the other hand, a couple of subsequent studies [130; 131] failed to reveal the preponderance of low-frequency band of SW activity in patients with IBS as previously reported [128].  
Bioelectrical signatures of constipation and diarrhea have been the focus of several studies as well. [PERSON] et al. performed measurements from the mucosal surface of patients with constipation and diarrhea [132]. The findings were consistent with earlier studies and reported the existence of low-frequency and high-frequency SW rhythms in the colon. In addition, spike bursts of either short or long duration were reported. Constipation patients had a 2-4-fold increase in the number of short duration spike bursts compared to controls, whereas diarrhea patients had an absence of short duration spike bursts and a reduction of the number of long duration spike bursts (3-8 vs. 20-26 spike bursts per hour) [132]. In a similar study performed on constipation patients, meal ingestion resulted in a moderate increase in spike bursts, whereas a prompt and significant increase was observed in healthy subjects [133]. In addition, SW activity was also reported to be impaired in patients with constipation, with no SWs recorded from the entire colon in more than half of the constipation patients, and weak activity was observed in the right colon in the rest of the patients [134]. Such impaired SW activity may be related to a deficit of ICC in the colon of patients with constipation [135].