Pain researchers such as Tamar Makin (Oxford) and Marshall Devor (Hebrew University, Jerusalem) argue that phantom limb pain is primarily the result of "junk" inputs from the peripheral nervous system.Despite a great deal of research on the underlying neural mechanisms of phantom limb pain there is still no clear consensus as to its cause. Both the brain and the peripheral nervous system may be involved.Research continues into more precise mechanisms and explanations. Neural mechanisms
Pain, temperature, touch, and pressure information are carried to the central nervous system via the anterolateral system (spinothalamic tracts, spinoreticular tract, spinomesencefalic tract), with pain and temperature information transferred via lateral spinothalamic tracts to the primary sensory cortex, located in the postcentral gyrus in the parietal lobe, where sensory information is represented somatotropically, forming the sensory homunculus.In phantom limb syndrome, there is sensory input indicating pain from a part of the body that is no longer existent. This phenomenon is still not fully understood, but it is hypothesized that it is caused by activation of the somatosensory cortex. Treatment
Most approaches to treatment over the past two decades have not shown consistent symptom improvement. Treatment approaches have included medication such as antidepressants, spinal cord stimulation, vibration therapy, acupuncture, hypnosis, and biofeedback. Reliable evidence is lacking on whether any treatment is more effective than the others. Most treatments are not very effective. Ketamine or morphine may be useful around the time of surgery. Morphine may be helpful for longer periods of time. Evidence for gabapentin is mixed.
Functional gastrointestinal disorders (FGID), also known as disorders of gut–brain interaction, include a number of separate idiopathic disorders which affect different parts of the gastrointestinal tract and involve visceral hypersensitivity and motility disturbances. Classification
Terms such as functional colonic disease (or functional bowel disorder) refer in medicine to a group of bowel disorders which are characterised by chronic abdominal complaints without a structural or biochemical cause that could explain symptoms. Other functional disorders relate to other aspects of the process of digestion.The consensus review process of meetings and publications organised by the Rome Foundation, known as the Rome process, has helped to define the functional gastrointestinal disorders. Successively, the Rome I, Rome II, Rome III and Rome IV proposed consensual classification system and terminology, as recommended by the Rome Coordinating Committee. These now include classifications appropriate for adults, children and neonates/toddlers.The current Rome IV classification, published in 2016, is as follows:A. Esophageal disorders

A1. Functional chest pain
A2. Functional heartburn
A3. Reflux hypersensitivity
A4. Globus
A5. Functional dysphagiaB. Gastroduodenal disorders

B1. Functional dyspepsia
B1a. Postprandial distress syndrome (PDS)
B1b. Epigastric pain syndrome (EPS)
B2. Belching disorders
B2a. Excessive supragastric belching
B2b. Excessive gastric belching
B3. Nausea and vomiting disorders
B3a. Chronic nausea vomiting syndrome (CNVS)
B3b. Cyclic vomiting syndrome (CVS)
B3c. Cannabinoid hyperemesis syndrome (CHS)
B4. Rumination syndromeC. Bowel disorders

C1. Irritable bowel syndrome (IBS)
IBS with predominant constipation (IBS-C)
IBS with predominant diarrhea (IBS-D)
IBS with mixed bowel habits (IBS-M)
IBS unclassified (IBS-U)
C2. Functional constipation
C3. Functional diarrhea
C4. Functional abdominal bloating/distension
C5. Unspecified functional bowel disorder
C6. Opioid-induced constipationD. Centrally mediated disorders of gastrointestinal pain

D1. Centrally mediated abdominal pain syndrome (CAPS)
D2. Narcotic bowel syndrome (NBS)/ Opioid-induced GI hyperalgesiaE.