siick.

Feeling Pain and Being in Pain

science:

So memory isn’t so simple. You know what else turns out to be unexpectedly complex? Pain. Pain is unpleasant. When something hurts, we don’t like it. Right? Now, there exist cases of congenital analgesia, or hereditary inability to feel pain. And most of us have experienced the effects of local anesthetics, so it’s not entirely out there to imagine that someone could experience normally painful stimuli and not feel it. But there is one puzzling, extremely rare medical condition that seems to challenge the commonsensical idea that pain is always unpleasant: it’s called pain asymbolia.

Unlike people who can’t feel pain, patients with pain asymbolia can feel it alright. They can detect pain, and discriminate between different kinds of pain, pains located in different parts of the body, and of varying intensity. It just doesn’t bother them. They don’t suffer from pain at all: they experience no unpleasantness, have no urge to escape painful stimuli, and don’t act to avoid them. They don’t flinch if you light a match near their face or move a needle towards their eyes. In fact, they seem completely incapable of learning how to avoid painful or harmful situations, and seem oblivious to the fact that their pain response is unusual. There’s a total disconnect between the perceptual aspect of pain and the emotional aspect that motivates us to avoid it. They feel pain, but it doesn’t hurt.

Scientists have even been able to pinpoint some of the neural basis for this weird non-painful pain. Patients who present with pain asymbolia usually turn out to have damage to the granular insula and parietal operculum. It’s theorized that this area is responsible for the emotional aspect of pain, the unpleasantness and hurt of it. In particular, studies in monkeys have identified an interesting area of the brain called Brodmann area 7b, where neurons seem to respond to painful heat and where activation closely corresponds with avoidant behavior—these neurons light up when the monkey’s pain receptors perceive an increase beyond the threshold for tissue damage, and as they do, the monkeys scamper off from the hot surface. Interestingly, some of the neurons in this area also respond to threatening visual stimuli:

Some neurons responded when the animal was shown an undesired, noxious object, such as a pin that has just been used to deliver a slightly painful prick. These responses stopped, following repeated visual presentation of the pin, or after a lapse of 10-15 minutes. However, a response could be elicited by showing the pin if this object was again used to apply a painful stimulus. Visual presentation of neutral objects … did not elicit responses from these neurons.

This could explain why patients with defects in this area would be unresponsive to both pain and threatening visual stimuli, and unable to learn avoidant behavior conditioned by threatening visuals.

The linked pdf is book length, and goes into depth about pain asymbolia, and just what such abnormal cases tell us about what pain really is.

December 01, 2011