Lecture 6.docx

Lecture 6: The Causes of Play – The ‘Why’ of Mechanism Problem: More data than theories Is Play a Unique Behavior or a Modified Version of Other Behaviors? Theory 1: Play is an Immature Version of Developing Behavior Systems (e.g., sex, aggression, etc.) Developmental processes suggest so (Cuvier’s...

Lecture 6: The Causes of Play – The ‘Why’ of Mechanism Problem: More data than theories Is Play a Unique Behavior or a Modified Version of Other Behaviors? Theory 1: Play is an Immature Version of Developing Behavior Systems (e.g., sex, aggression, etc.) Developmental processes suggest so (Cuvier’s gazelles) Immature behaviors are incomplete, so different components emerge in a piecemeal fashion… as seen in the development of gull display Immature animals are clumsy, have less well-developed sensorimotor systems, making the performance of behavior patterns less coordinated than that of adult performance Testing the Hypothesis of Immaturity Stone play in macaques Performed by both juveniles and adults Many of the behavior patterns are derived from foraging Adult male long tailed macaque using a stone to pound a nut Juvenile long tailed macaque pounding a stone with another stone Comparing across age and context If theory 1 is correct, you would predict that the adult movements should be more coordinated in both contexts and differ from the juveniles when pounding stones Prediction not upheld: In adults stone pounding and nut pounding differ, and the stone pounding of adults and juveniles is similar Theory 1 – Evaluated There is a play-typical pattern of action that is true whether the animals are adults or immature This is well documented in play fighting, in which both adults and juveniles follow the same rules (see Pellis & Pellis, 2010, Chapter 6, p. 135; Chapter 7, pp 147-148) Therefore, while immaturity may account for some of the differences between how juveniles and adults play, this theory does not explain the presence of play itself Theory 2: Play is a By-Product of Having of Large Brain Mammals have larger brain than other vertebrate taxa and they are more playful, and humans have the largest brains among mammals and are the most playful mammals. Problems with the scala naturae view: It only looks at size, so misses the fact that the basic organization of the vertebrate brain is conserved across taxa Many different lineages have expanded brain size, so it is not an evolutionary event Obviously a blue whale is going to have a larger brain than a baboon, but it also has a much larger body – need to compare brain size to relative body size. Elephant Nose Fish Relative to body size the brain is larger than that of humans Fish: Brain = 3% of body mass and uses 60% of energy (oxygen) Human: Brain = 2% of body mass and uses 20% of energy (oxygen) The baboon has a brain size that is greater than expected for an animal of its size, whereas the blue whale has a brain size smaller than expected for its size. The extra neural tissue available to the baboon suggests that it has greater processing capacity. Comparing Brains Relative to Bodies As overall body size increases, brain size increases, but only at a fraction of body size (estimates range between 0.67 and 0.75) Even if the slope is identical between two lineages, where it intercepts the Y-axis can differ, suggesting an overall difference in absolute brain size achievable by a lineage. The mathematical relationship describing the relationship between brain size and body size is Y = aXb (where Y = brain size, X = body size, a = Y intercept, and b = slope) In reality there is variation in both a and b across lineages, but the overall pattern looks similar Is Play More Prevalent in Animals with Larger Brains? A comparison of mammalian orders – orders containing species with larger brains, are significantly more likely to play However, as the analysis was shifted to lower taxonomic levels, families, genera, and species, the correlation declines and in most cases disappears. Three Problems: (1) It may depend on the type of play Social players (most) vs non-social players (medium) vs non-players (least) (2) Comparing overall brain size rather than components of the brain may miss relevant relationships Social play shows a significant correlation in striatum size in primates (3) There may be a combination of play type and brain component Social play shows a significant correlation in striatum size in primates Non-social play not significant So it may be true, larger brained species are capable of more complex cognition and behavioral flexibility and this translates into a greater propensity for play. What Changes with Increased Brain Size? Larger brains slows down development resulting in a longer post birth period allowing the opportunity for more play. In rodents, maturity after birth much quicker than in primates Over 30% of the increase in brain size is attributable to a disproportionate increase in the cerebrum, yet… Decortication at birth does not make rats less playful Either directly or indirectly increases in brain size does make play more likely, but why don’t all animals with large brains play? Theories of Play Theory 1: Play is an immature version of developing behavior systems (e.g., sex, aggression, predation, etc.), so no special mechanisms needed. But the theory does not explain all play. Theory 2: Play is a by-product of having a large brain, so no special mechanisms needed. But the theory does not explain all play Theory 3: Play is a unique behavior system Three-spine stickleback Tinbergen’s Lattice Hierarchy Model Male stickleback attacks other males that intrude on their territory Sign Stimulus for Fighting = red belly Sign Stimulus for Courtship = Swollen Belly Konrad Lorenz Psychohydraulic Model Aggression builds up in a reservoir over time, and a sign-stimulus or releasor unleashes the built-up aggression, resulting in aggressive behaviours. It involves a reservoir (drive), a release mechanism, a stimulus which "unplugs" the reservoir, and resulting behaviours upon release. Once the internal pressure to be aggressive builds up enough, a sign stimulus releases it, triggering aggression. Motivation increases over time, so the reservoir builds up over time. Motivation in animal behaviour is specific to the behaviours it triggers (e.g., when a species needs to mate or secure food). Combining the Models Theory 3: Play is a Unique Behavior System Two broad options: Play is a singular behavior system that can incorporate behavior patterns from many other behavior systems Play as a behavior system that can borrow behavior patterns from multiple other behavior systems. E.g., Aggression & Sex & Predation = Play Behavior System If so, behavior patterns from multiple behavior systems should be mixed in novel combinations Mixed play (social and object) Two Types of Fighting in Richardson’s Ground Squirrels A. Aggressive play Behaviors that stimulate aggressive interactions, but not driven by hostility May include chasing, mock biting, wrestling, and vocalizations Characterized by reciprocal actions between individuals; each taking turns as aggressor and recipient Establish social bonds, practice combat, reinforce social hierarchies within the group Occurs between same-sex or opposite-sex individuals; commonly observed in juveniles as they develop B. Sexual play Behaviors that mimic courtship or mating rituals Behaviors such as chasing, mounting, nuzzling Occurs between individuals of opposite sexes Create social bonding, exploration of social roles and practice of courtship behaviors Help individuals develop social and mating skills, establish social bonds, and navigate reproductive relationships within the population. Are Aggressive and Sexual Play Mixed? If the single play behavior system is correct, then predict that counterattacks should be equally likely from one form to the other Are Types of Play Fighting Mixed? Not in ground squirrels Not in grasshopper mice which engage in sexual play and predatory play Not in mouse lemurs which engage in aggressive play, affinitive play and sexual play Play can arise from many different behavior systems and so there are many play behavior systems Play as multiple behavior system that borrows behavior patterns from only one other behavior system Asian small clawed otter Social play & Object play Majorly object play for foraging up until feeding time, then social play takes over Limitation of the Study: One group of 12 otters at the Melbourne Zoo Recently replicated with 4 groups (11 otters) from three zoos Theory 3 Evaluated Different types of play appear to have organizational coherence (behavior system relevant behavior patterns co-occur in sequential order) and at least in some situations many of the same central control mechanisms are involved. What About Behavior Patterns Common Across Different Behavior Systems? Lets consider mounting again Same behavior co-opted in different context Female Intruder = Sexual mounting used for copulation Male Intruder = Aggressive mounting used for asserting dominance Hypothalamic Stimulation Two different forms of attack produced by stimulation of different systems within the hypothalamus (rage display or quiet biting) Key Brain Areas (Both in the Hypothalamic Area) Sex = medial preoptic area Aggression = ventromedial hypothalamus (subdivision vl) Most behavior patterns that are used within a behavior system are correlated with those within that behavior system and many that resemble those used in other behavior systems are in fact often independent The theory that play is not a single ‘play behavior system’, but that there are multiple and largely independent ‘play behavior systems’ seems most consistent with the available data A Promising Possibility The play fighting in rats is derived from the sexual behavior system, whereas as that of rhesus monkeys and chimpanzees is derived from the aggressive behavior system Yet, there seems to be convergence on tapping into the same basic neural circuitry. Thus, even though there may be different types of ‘play behavior systems’, there may be common mechanisms that can coalesce these different systems together If combining behavior from different behavior systems occurs as a result of distinct play behavior systems coalescing, then play involving mixed behavior patterns should be a derived state. A Test of the Hypothesis Some primates engage in play fighting that simulates both sexual (amicable) behavior and aggressive behavior Whether behavior patterns from these two behavior systems are combined was assessed for a variety of species and this was then mapped on a cladogram. Prediction Supported: Combining types of play is a derived character state, supporting the theory that the origin of play involves multiple independent play systems. Theories Evaluated Play is an immature version of developing behavior system (e.g., sex, aggression, predation, etc.) Play is a by-product of having a large brain Play is a unique behavior system Mechanisms common to all theories Social Play Most Intensely Studied Studies with young chimpanzees have shown that they preferentially open a peep hole to see a pair of juvenile playing and do so even if they are hungry. That is, they are so motivated to play that even vicarious play experience can trump being moderately hungry. Rats have been particularly useful in exploring the mechanisms that produce and regulate play Ivan Pavlov – Classical Conditioning Classical conditioning is a type of learning in which an organism comes to associate a neutral stimulus with a meaningful stimulus, eventually eliciting a reflexive response to the previously neutral stimulus alone. Male Stickleback attacks other males that intrude on their territory – classical conditioning New behavior is not learned, rather the stimuli capable of triggering built-in behavior patterns can be switched Such learning can be readily integrated with both Tinbergen’s lattice hierarchy and Lorenz’s Psychohydraulic models (and with Hogan’s formulation of Behavior Systems) Operant Conditioning Procedures Have Shown That: Rats will go to a box in which they had previously interacted with a playful peer and that they will work to gain access to such a partner. That is, they are motivated to play. But it has become clear that there are two ways in which motivation can be modified – wanting to do X and liking the experience of doing X and these processes are mediated by two independent but interacting neural systems Wanting = Dopamine Liking = Opioids Dopamine is essential for making rats ‘want’ to play and that endogenous opioids are essential for allowing rats to ‘like’ engaging in play Complicating the picture is that there are several neurochemical systems that can modulate the dopamine and opioid systems, allowing for ways to fine tune what is both wanted and liked, with new details on the neural contributions growing yearly Nodes in the Neural Circuitry of Play PFC, Amyg, MC, OB The brainstem circuits provide the behavior patterns, midbrain and lower forebrain circuits provide motivational and motor regulation and the cortex provides emotional and cognitive regulation Unlikely this forms a circuit unique to play It is possible that the dynamic interactions among elements of this circuitry are unique for different behavior systems. Progress in measuring such circuitry activity in freely behaving rats may eventually be able to determine if this is the case. Limits of the Rat Model Rats predominantly engage on social play, so we do not know two things: (1) Can the findings be generalized to other species? (2) Can the findings be generalized to other forms of play? Work on hamsters have identified some of the same nodes and comparative studies of primates show that the same neural systems important for regulating social play in rats are expanded in size in primate species that engage in more social play. So, there may be similar circuits involved in the social play of other mammal species. The comparative data on primates also show that those neural systems that are expanded in species that engage in more social play are not similarly expanded in species that engage in more non-social play.