The cardiac general visceral sensory pain fibers follow the sympathetics back to the spinal cord and have their cell bodies located in thoracic dorsal root ganglia 1-4(5).

The central nervous system (CNS) perceives pain from the heart as coming from the somatic portion of the body supplied by the thoracic spinal cord segments 1-4(5).

Myocardial infarction can rarely present as referred pain and this usually occurs in people with[4] diabetes or older age.

Furthermore, he believed that non-nociceptive afferent inputs to the spinal cord created what he termed "an irritable focus".

The delay in appearance of referred pain shown in laboratory experiments can be explained due to the time required to create the central sensitization.

Experiments involving noxious stimuli and recordings from the dorsal horn of animals revealed that referred pain sensations began minutes after muscle stimulation.

According to hyperexcitability, new receptive fields are created as a result of the opening of latent convergent afferent fibers in the dorsal horn.

Neuroimaging techniques such as PET scans or fMRI may visualize the underlying neural processing pathways responsible in future testing.

However, pain studies performed on monkeys revealed convergence of several pathways upon separate cortical and subcortical neurons.

[citation needed] Pain is studied in a laboratory setting due to the greater amount of control that can be exerted.

[citation needed] In recent years several different chemicals have been used to induce referred pain including bradykinin, substance P, capsaicin,[8] and serotonin.

This spatial summation results in a much larger barrage of signals to the dorsal horn and brainstem neurons.

A case study done on a 63-year-old man with an injury sustained during his childhood developed referred pain symptoms after his face or back was touched.

The study concluded that his pain was possibly due to a neural reorganization which sensitized regions of his face and back after the nerve damage occurred.

This conclusion was based on experimental evidence gathered by V. S. Ramachandran in 1993, with the difference being that the arm that is in pain is still attached to the body.

[citation needed] From the above examples one can see why understanding of referred pain can lead to better diagnoses of various conditions and diseases.

[citation needed] Studies have reported that the majority of patients that experienced centralization were able to avoid spinal surgery through isolating the area of local pain.

McKenzie showed that the referred pain would move closer to the spine when the patient bent backwards in full extension a few times.

[10] As with myocardial ischaemia, referred pain in a certain portion of the body can lead to a diagnosis of the correct local center.

The study was conducted on patients with fibromyalgia, a disease characterized by joint and muscle pain and fatigue.