PLAY: an Innate Brain System
"To the best of our knowledge," writes Jaak Panksepp in Affective Neuroscience: The Foundations of Human and Animal Emotions (1998), "a basic urge to play exists among the young of most mammalian species…." He recounts Jane Goodall's experience with chimpanzees: "A chimpanzee infant has his first experience of social play from his mother as, very gently, she tickles him with her fingers or with little nibbling, nuzzling movements of her jaws. Initially these bouts are brief, but by the time the infant is six months old and begins to respond to her with play face and laughing, the bouts become longer."
Before initiating play, animals must be comfortable. "Indeed, when placed in new environments, animals typically exhibit strong exploratory activity with little tendency to play until they have familiarized themselves with the new surroundings," writes Panksepp. "In all species that have been studied, playfulness is inhibited by motivations such as hunger and negative emotions, including loneliness, anger, and fear." Panksepp points out that in "most primates, prior social isolation has a devastating effect on the urge to play. After several days of isolation, young monkeys and chimps become despondent and are likely to exhibit relatively little play when reunited. …" He notes that playfulness returns "only when confidence has been restored." Rodents respond differently to isolation. "Laboratory rats show a greater emotional equanimity in coping with social isolation as compared to many other mammals." writes Panksepp. "Prior social isolation systematically increases roughhousing play in juvenile rats, while social satiation systematically reduces it."
While hunger reduces play behavior in young rats, "a single meal brings play right back to normal," reports Panksepp. "It may come as a surprise to some, but young rats given no other ludic [from ludare, meaning 'to play'] outlets love to be tickled by and play with a frisky human hand." He points out that juvenile rats exhibit rough-and-tumble play behaviors "even if they have been prevented from having any prior play experiences during earlier phases of development." Panksepp explains that young rats start to play around 17 days of age, and if denied social interaction throughout the early phases of psychosocial development (e.g., from 15 to 25 days of age), "they play vigorously as soon as they are given their very first opportunity." Panksepp concludes that the impulse for rough-and-tumble play "is created not from past experiences but from the spontaneous neural urges within the brain."
The rough-and-tumble PLAY system "is important for learning various emotional and cognitive skills," Panksepp emphasizes, "including aspirations for social dominance and cooperation, which influence behavior with different intensities throughout the life span of each animal." He explains that "play may allow young animals to be effectively assimilated into the structures of their society. This requires knowing who they can bully, and who can bully them. One must also identify individuals with whom one can develop cooperative relationships, and those whom one should avoid." Panksepp points out that "the most vigorous play occurs in the context of preexisting social bonds." In contrast, he says that if "one animal becomes a 'bully' and aspires to end up on top all the time, playful activity gradually diminishes and the less successful animal begins to ignore the winner."
"Play probably allows animals to develop effective courting skills and parenting skills," writes Panksepp, "as well as increasing their effectiveness in various aspects of aggression, including knowledge about how to accept defeat gracefully." He points out that "PLAY circuitry allows other emotional operating systems, especially social ones, to be exercised in the relative safety of one's home environment. Thus, in the midst of play, an animal may gradually reach a point where true anger, fear, separation distress, or sexuality is aroused." Panksepp notes, however, that serious aggressive postures and sexual-type behaviors are rarely seen in play-fighting. During the later stages of juvenile life, because of their larger size and stronger competitive urges, more mature male animals may appear to play more vigorously than their smaller companions. This difference, Panksepp explains, may in part reflect the drive to attain male dominance. He writes: "It is certainly possibly that PLAY systems contribute to social dominance urges, which may help explain our love of rough professional sports, where such issues are paramount in the minds of players and spectators alike."
Regarding the nonsocial functions of PLAY neurocircuitry, Panksepp points out that play increases physical fitness, skillful tool use, and the ability to innovate and think creatively. Young predators learn to hunt and prey species learn how to avoid predators. He writes: "Indeed, perhaps play even allows animals to hone deceptive skills, and thus in humans may refine the ability to create false impressions."
PLAY neurocircuitry appears to be "intimately linked to somatosensory information processing within the midbrain, thalamus, and cortex," explains Panksepp. John A. Beal, Department of Cellular Biology and Anatomy, Louisiana State University, provides the image below. I have added labeling for these three areas of the brain. We discuss sensory information processing in Part 1 of MyBrainNotes.com in The brain's motor and somatosensory cortical maps.
PLAY neurocircuitry certainly helps young animals learn to interact with their environment since somatosensory information is obtained from the sense organs, such as the eyes and ears. Touch is also a form of somatosensory information. Generally speaking, somatosensory neurosignaling conveys information about the state of the body and immediate environment, such as body position and ambient temperature.
Within the thalami, Panksepp notes that somatosensory information is projected in two directions—up to the parietal cortex that processes bodily sensations and into nonspecific thalamic nuclei that elaborate a playful motivational state. He points out that bilateral damage to thalamic areas involved in PLAY circuitry reduces both pinning and dorsal contacts and that "lesioned animals are no longer motivated to play." Panksepp reports that in such lesioned animals, "other relatively complex motivated behaviors, such as food seeking (foraging), are not diminished." John A. Beal, Department of Cellular Biology and Anatomy, Louisiana State University, provides the image above (links to source).
Panksepp emphasizes that PLAY behavior is an "endogenous urge" within the brain and does not necessarily rely on somatosensory input. In rats, "neither vision nor olfactory senses (including vibrissae) are necessary for the generation of normal play." He points out that the "auditory system contributes positively to play to some extent, since deafened animals play slightly less, and rats do emit many 50-KHz laughter-type chirps both during play and in anticipation of play." Panksepp explains that touch is the sensory system that helps most in instigating and sustaining normal play. Regarding experiments to test the importance of touch in generating PLAY behavior, Panksepp writes: "Local anesthetization of the neck and shoulder area is highly effective in reducing the level of playful pinning in young rats even though the motivation for play, as measured by dorsal contacts, is not reduced." Citing laboratory evidence, Panksepp concludes that "rats have specialized skin zones that send play signals into the nervous system when they are touched. In other words, mammals appear to have 'play skin,' or 'tickle skin,' with specialized receptors sending information to specific parts of the brain that communicate playful intentions between animals."
In animals that have had their cortex removed, "play solicitations and overall roughhousing, as monitored by direct activity measures, remain intact," writes Panksepp, although pinning behavior is reduced by about half. "It seems clear that play has powerful effects on the cortex." Panksepp concludes that juvenile play "involves programming various cortical functions." He writes: "In a sense, the cortex may be the playground of the mind, and PLAY circuits may be a major coordinator of activities on the field of play."
Panksepp asserts that "the hallmark of PLAY circuitry in action for humans is laughter, a projectile respiratory movement with no apparent function, except perhaps to signal to others one's social mood and sense of carefree camaraderie." (Photo courtesy of David Shankbone.)
"Laughter," Panksepp explains "is not learned by imitation, since blind and deaf children laugh readily." Ethologists consider genuine laughter to be innate and primal. The social smile is more contrived. In Part 1 of MyBrainNotes.com, we discuss the emotional versus the social smile in
The anterior cingulate cortex–emotion, attention, and working memory.
Panksepp notes that "an openmouthed display characterizes the most intense forms of human laughter, and similar gestures are used as signals for play readiness in other species such as chimpanzees and dogs." He adds that chimpanzees' reunion rituals, "especially after long separations, are typically characterized by a lot of hooting, howling, and touching."
Other evidence indicating that specific neurocircuitry in the brain generates laughter is that "amylotrophic lateral sclerosis (ALS), a demyelinating disease that affects the brain stem," according to Panksepp, "can release impulsive laughter." He also points to "gelastic epilepsy, which is accompanied by bouts of laughter."
Previously, in Attention, Learning, and Memory: The VIGILANCE System, we learned that in ADHD, due to low levels of norepinephrine and perhaps, dopamine, the prefrontal cortex fails to adequately inhibit inappropriate impulses or distractions. Panksepp postulates that "many children diagnosed with ADHD may, in fact, be exhibiting heightened play tendencies." He writes:
Their hyperactivity, impulsiveness, and rapid shifting from one activity to another may be partly due to their unconstrained and unfocused playful tendencies. Indeed, the medications that are used to treat the disorder—psychostimulants such as methylphenidate (i.e., Ritalin) and amphetamines—are all very effective in reducing playfulness in animals. Moreover, parents of hyperkinetic children often complain that one of the undesirable side effects of such medications is the reduced playfulness of their children. Obviously, parents value these childlike characteristics and are typically disturbed when the children's natural playfulness is pharmacologically diminished.
"Virtually all investigators now agree that autism is a neurobiological disorder," writes Panksepp in Affective Neuroscience. He explains that compared to normal brain development, people with autism have "an undersized cerebellum and brain stem, and a larger than normal cerebrum," along with "too many densely packed small neurons within parts of the limbic system, suggesting that selective cell death, a natural process of the developing brain called apoptosis, has not progressed normally." The result is that in autistic individuals, subcortical or so-called limbic structures do not interconnect with the rest of the brain as well as they normally would.
Panksepp quotes Leo Kanner, who in 1943 proposed that autistic children "have come into the world with an innate inability to form the usual, biologically provided affective contact with people." Panksepp reports that the "current theoretical perspective is that these children do not develop a 'theory of mind,' which refers to the ability of most children past the age of 2 to begin recognizing the types of thoughts and feelings that go on in the minds of others."
The motivation for rough-and-tumble PLAY, Panksepp points out, "is practically the only social desire that autistic kids exhibit at a relatively high level, but not with the reciprocating give and take and fantasy structures of normal childhood play." He notes that rats treated with low doses of opioids, like autistic children, do not exhibit a high desire for social companionship except for rough-and-tumble play. Panksepp proposes that "autistic children may have been exposed to excessive levels of endogenous opioids, or related molecules, during early development." He writes:
Moreover, they may continue to experience excessive opioid activity within certain circuits of their brains as they mature. This could explain their pain insensitivity and consequent tendency to exhibit self-injurious behavior, as well as many other symptoms ranging from stereotypies to social aloofness. Because of these considerations, it has been suggested that some benefits may be brought to these children by the administration of opiate receptor blocking agents such as naltrexone.
Naltrexone may improve the lives of those autistic children "who have high circulating levels of opioids in the brain, a condition that has been demonstrated in about half of all autistic children who have been tested," explains Panksepp. "Moderate doses of naltrexone can reduce some of the active symptoms of autism such as overactivity, stereotypies, and self-injurious behaviors, and in low infrequent doses, it can promote social activities."
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