Lesion Studies and Pain
Observations of patients with frontal lobotomies provided some of the first evidence that the frontal cortex was involved in pain perception. Before the invention of psychotropic drugs, lobotomies were used for treating schizophrenia, manic depression, and reducing chronic pain in non-psychiatric patients. Psychosurgery (lobotomy) was performed by severing the prefrontal cortex from the rest of the brain. In the early part of this century, psychosurgery was crude and the whole prefrontal cortex was cut (Freeman and Watts, 1950). By 1946, a method of cutting just the frontal parts of the prefrontal cortex was introduced (Freeman and Watts, 1950). This procedure called cingulotomy, is still used today to treat intractable pain in some cancer patients (Sweet, 1982). Cingulotomy is more effective and causes fewer side effects compared to the old style of lobotomy.
After a lobotomy, patients with chronic pain or depression often regained the ability to function normally and retained their general intelligence, but they lost all emotional depth and feeling (Freeman & Watts, 1950; Foltz & White, 1962; Hurt & Balliantine, 1974). Their emotional experience was greatly reduced after lesioning of the prefrontal cortex, and patients with the largest areas of the prefrontal cortex disconnected had the greatest effects. However, lobotomy patients retained normal pain reflexes and would pull away when a doctor manipulated an injured area of their body. They disliked momentary pain yet were indifferent to the pain of their disease (Freeman & Watts, 1950). A patient might scream when a doctor manipulated a tender body part, but the next minute he was smiling after the painful manipulation was stopped. Their behavioral reactions seemed disjointed. Lobotomy patients experienced pain, but did not experience the emotional feeling of pain. The patients reaction to a painful medical procedure was entirely in the present. They seemed to have lost the fear of pain.
More recently, pain research on humans show that a mildly painful stimulus applied to the hand increases blood flow in the frontal cortex (Smith and Boyd, 1991), and a PET scan study by Rainville, et al (1997) provided direct experimental evidence linking the PFC with the emotional component to pain. By using hypnotic suggestions to both increase and decrease a pain sensation, significant changes in pain-evoked activity was found in the anterior cingulate cortex. This is consistent with the clinical observations made in lobotomy patients. A more recent study on chronic pain which causes long-term suffering showed that activity in the frontal cortex was increased (Apkorian et al., 2001). Fulbright et al. (2001) found that pain and basic sensory input are processed in different parts of the brain. A painful cold water stimulus activates the anterior circulate and a non-painful cold stimulus only activates sensory areas.
Lesion studies in rats indicate that the frontal cortex has similar functions in rodents and humans. Lesions in the frontal cortex of rats impairs behavioral flexibility and the organization of species typical behaviors (Kolb and Tees, 1990). In both humans and rats, frontal cortex lesions cause behaviors to become disjointed and fragmented (Freeman and Watts, 1950; Kolb and Tees, 1990). Even the small frontal cortex in the rat brain performs the same functions as mammals with more complex brains (Kolb and Tees, 1990). Therefore, it is likely that the frontal cortex in rats is involved in pain perception in a similar manner as humans.
Suffering in Reptiles and Birds:
After reading many articles about frontal cortex anatomy in warm blooded animals, we became convinced that rats, cats, dogs, horses and cattle can suffer from long term pain which is true pain. The fact that rats with chronic pain will actively seek analgesics is convincing evidence of suffering, or serious discomfort. What about birds, reptiles and fish? Research on de-beaked chickens shows they pain guard after the procedure and will reduce food intake. De-beaked chickens are reluctant to use their beaks. Sometimes a neuroma forms on the end of the beak after it heals. Neuromas can cause pain in man (Gentle, et al 1990). Chickens with neuromas reduce the number of pecks at feeding (Gentle, et al 1990; Duncan et al 1989). We agree that mammals from rats, cats, and dogs would have similar degrees of suffering when subjected to a painful procedure. However, it is likely that birds may experience pain differently. Recent work by Gentle (1997) show that decebrate chickens will still pain guard legs injected with a substance that causes pain. The results suggest that in chickens, pain from chronic arthritis is organized in the brainstem. However, if the chickens beak is trimmed and the frontal area of the brain is removed, pain guarding and other pain related behaviors are absent. But, if the beak is trimmed six days after the frontal area of the brain is removed, the chicken continues to pain guard (Gentle, et al 1997). It appears that chickens are unable to process two emotions simultaneously. Chickens may suffer from chronic pain when they are undisturbed, but when disturbed or frightened, the pain ceases and the chicken can only attend to the fear (Gentle and Corr, 1995). Prelaying behavior and feeding motivation can completely suppress pain coping behaviors in arthritic chickens (Gentle and Corr, 1995; Wylie and Gentle, 1998). Turkeys with degenerative hip disorders reduce spontaneous activity and sexual activity (Duncan et al 1991). The authors conclude that the different systems in a birds brain may be less integrated than in higher mammals. A bird may be more mono channel and operate only one system at a time. The bird would probably be suffering if the pain or fear channel is operating.
Do reptiles or amphibians suffer from pain? Research shows that the nervous system of amphibians responds to analgesic drugs. Amphibians will respond to a painful stimulus applied to the skin. Many different types of analgesic drugs will reduce the response (Stevens et al., 1994; Stevens et al., 2001). Is this true suffering from pain or is it just a reflex like touching a hot stove?
Do reptiles and amphibians pain guard or seek analgesics? Both these areas need to be researched. The antedotes below may provide some insights for guiding future research. Discussions with reptile specialists indicate that reptiles may or may not pain guard. Friend (1998 personal communication) indicates that igaunas will walk on a severely damaged leg and make no attempt to reduce weight on the damaged limb. Igaunas are physically capable of lifting a leg to favor it, but they do not. Lizards react to noxious stimuli which may cause acute pain, but may have little reaction to injuries that would cause long term pain. However, Friend (1998) was adamant that reptiles experience pain, but when we discussed pain guarding behavior and chronic pain, she stated; I never thought about that before. Discussions with Dr, Fredrick Fry a reptile veterinarian at the University of California indicated that there are signs of pain guarding in other reptiles. A tortoise with a sore mouth will not eat and if it has a sore toe it will not walk. This is likely to be true pain guarding. Snakes with a damaged mouth may refuse to eat or lie on their backs to avoid pain. A tortoise with an abscess in its head will refuse to eat. Eating resumes shortly after the abscess is drained. Even fish pain guard. Dr. Steve Kestin, University of Bristol states that a fish with an inflamed gut will reduce activity. Maybe this can be explained by weakness from sickness. However, the fish will swim normally when it is chased with a net. Dr. Kestin also says a fish will avoid the place where it has been hooked or shocked. Rakover (1979) reports that fish can easily learn to avoid an aversive fear arousing stimulus by swimming away. In these situations it is impossible to separate fear from pain. Feelings of fear are very aversive and subjecting any animal to situations which cause it to be highly fearful would be very detrimental to its welfare.