Bowsher Explodes Pain Theory

David Bowsher’s criteria for Central Pain have long been utilized by authors at painonline. Now Dr. Bowsher has destroyed ages old theories of where pain is located in the brain. This is the most important and most revolutionary concept of pain in the brain which has yet come to light.

Dr. Bowsher is remembered in some circles as the doctor who described central pain burning as a “glow of pain” meaning that it lacks the discriminative features of ordinary pain (location, speed, quality, etc.) and is like “the afterburn of touching a hot stove”. (We have elsewhere linked this burning sensation to the effect of real acids in the area around pain neurons, acids such as fatty acids, arachidonic acid and the prostaglandins and eicosanoids, cytokines, interleukins leukotrienes, potassium, etc.–see “acid” elsewhere at this site)

Dr. Bowsher’s brilliance in the field of central pain probably cannot be overstated and we owe a great deal to his colleagues and students as well. Now he has revolutionized pain theory and specifically the theory of central pain.

Pain theory has had a steady march backward in the brain. At one point, the emotional region of the brain, the frontal cortex was said to be the pinpoint of pain. Evidence for this came from the fact that certain brain ablation procedures in the frontal cortex or in the anterior cingulum* (just beneath the frontal cortex) were said to make the person less distressed about pain. (Brain ablation was done frequently in early times for schizophrenia, which is now managed by other means) See review of Roland Worz correspondence elsewhere at this site, regarding central pain in schizophrenics, called by him “cenesthetic” pain. (Use SEARCH for cenesthetic) The frontal cortex is still thought major in suffering from pain, but it is not clear what areas predominate in short term suffering and which in long term suffering.

Pain itself was considered to be in SI (postcentral gyrus). Then, its supposed focus moved backward a little to SII, in the part known as the operculum or lid (SII) of the parietal cotex, and in the last year or so was moved even further back in the brain to the insular cortex.

There is a fissure, which runs from left to right across the top of the brain, known as the central sulcus. If a “T” is drawn atop the brain the cross bar is the grove known as the central sulcus. The lobe of the brain in front of the cental sulcus is known as the frontal cortex. The ridge behind the sulcus is the postcentral gyrus. In back of the postcentral gyrus is the parietal lobe, with the Sylvian fissure separating the parietal lobe from the temporal lobe..

Where the central sulcus runs down the side of the brain, it almost reaches the lateral sulcus, which runs horizontally. In older textbooks, the lateral sulcus or groove was known as the “Sylvian fissure” (see Bowsher’s article below). From the side, the brain looks like the fingers extended against the thumb, as when a child tries to make a ducks head in a shadow. The gap seen between thumb and fingers, represents visually the lateral sulcus.

Below the lateral sulcus is the temporal lobe. If the frontal lobe and temporal lobe are gently moved back, the insular cortex is revealed, overlapped by more rapid growth of the other two lobes. The space between the insula and the temporal lobe is known as the lateral cerebral fossa and is the location of the middle cerebral artery, the most important artey in cerebral stroke. Discriminative sense of touch can be lost when the middle cerebral artery is blocked on the way to the cortex.

The rear rim of the central sulcus or central fissure is known as the postcentral ridge or postcentral gyrus. The postcentral gyrus was thought to be the primary sensory area, and was named SI, Accordingly. pain, being a sensation, was assigned the same location, in SI.

Later, it became apparent that an area in the parietal cortex (the operculum, or “lid”) also processed pain, and this was called SII, or the “secondary” sensory area. Incidentally, Einstein’s brain was noted for lacking an operculum, due to early overgrowth by the parietal cortex behind it.

Even later, a part further back in what is called the insular cortex was found to process pain as well. Dr. Francis Crick published one of the first articles attributing the “painfulness of pain” to the insular cortex, here at painonline.

Now Dr. Bowsher, always one of our favorites, has shown that we really have not known much about pain at all. His very elegant work involved only four patients, but these four had strokes and lesions in the cortex of the brain, WITHOUT ANY INJURY TO SI. The fact that SI was intact meant that whatever symptoms were present had to be attributed to areas other than SI (postcentral gyrus).

For reference concerning the following see Bowsher D, Brooks J, Enevoldson P. Eur Neurol. 2004 Nov 10;52(4):211-225

The four patient subjects were as follows.

1. Lesion in the parietal operculum

2. Lesion in the parietal operculum extending to the front of the insula.

3. Lesion on both banks (sides) of the sylvian fissure and the dorsal insula as well.

4. Lesion on the upper bank of the sylvian fissure.

Spontaneous pain for Bowsher means the same as when Ron Tasker used it. It is the spontaneous burning or dysesthetic burning thought to be carried in the spinothalamic tracts.

Subjects 1 and 2 had mild spontaneous pain. In the affected areas neither could feel skinfold pinch (mechanical pain).

Subjects 1 and 2 could not discriminate amounts of sharpness (pinprick).

Subjects 3 and 4 could discriminate sharpness.

Subjects 1 and 2, with spontaneous pain, had impaired warmth and cold and impaired pain from heat.

Subjects 3 and 4 retained warmth and cold and pain from heat.

All four subjects had impaired ability to discriminate temperatures.

Bowsher concluded that central pain alters the cortical mechanisms for the perception of thermal stimulus.

SPONTANEOUS PAIN ONLY OCCURS WHEN THERE IS INTERFERENCE WITH THERMAL SENSATION. (Our survey at the Wall/McHenry database suggests patients may possibly be found with spontaneous burning who do not have thermal allodynia**, but they are the exception).

Quoting from the abstract,

“Functional MRI (fMRI) studies following thermal stimulation in subjects 1 and 2 showed these areas, particularly SII, to be concerned with the reception of innocuous and noxious thermal stimuli, mechanical (skinfold pinch) pain and sharpness (pinprick), implying that SI is principally concerned with the reception of low-intensity mechanical stimuli, although it was activated in 1 of our fMRI-studied subjects by innocuous cooling.”

This study by Bowsher blows away all prior thought and theory on pain localization in the brain. One cannot speak of it without modifying belief to account for Bowsher’s findings.

When central pain occurs from injury to the cord, there is reason to believe that the chemical insult which flows from nerve injury travels to the thalamus at the center of the brain and reproduces the dysfunctional signal.

Where this signal is then routed determines how the brain will perceive it. Thus, if we have spontaneous central pain, as oopposed to elicited or evoked central pain, we should nearly always have some impairment of thermal sensation.

These results are entirely consistent with results from the survey data of the Wall/McHenry database. We endorse Dr. Bowsher’s conclusions. Perusal of the articles written here in the past demonstrates our own observations about thermal pain being separate from mechanical or touch pain.

Do not be ashamed of your symptoms even if your doctor does not accept them. Speak truly and time will bear you out. It is not your job to make your examiner comfortable with what he thinks he knows. Your job is to speak openly and as clearly as possible, and eventually existing theory will come around to your way of seeing things. We are articulate lab rats, and eventually the pain theorists will have to listen to us. Special thanks to all of you who have completed the survey. We believed you all along. Special thanks to the fine investigators of central pain, and to the clinicians who carry us along.

*anterior cingulum, and specific nuclei of the cingulum relating to pain. See under Search for cingulum at this site.

**allodynia is pain from a stimulus which is normally not painful, such as light touch or temperature change, especially the cold blast of an air conditioner.