CH2CH2NH2

OHHO

The Playful Mind

Play Behavior and the Neurobiology of Having Fun

References to “fun” in the scientific literature are few and far between

Is play fun?

• Ask any kid

• Rats will run a maze when the opportunity to play is the reward

• Rats will prefer an environment where they’ve played over an environment where they haven’t played

The questions of the day

• What exactly is play and how do we study it in a rat?• Is there a neural circuit for play?• Since dopamine is involved in everything else, is it

also involved in play?• Are there genes for playfulness?• Can studying play in rats tell us anything about

psychiatric conditions in human children?• Is this the “fountain of youth”?

What exactly is play and how do we study it in rats?

What exactly is play?

Play is repeated, incompletely functional behavior differing from more adaptive versions structurally, contextually, or ontogenetically, and initiated voluntarily when the animal is in a relaxed or unstressed state.

Burghardt (2001)

The many faces of play

• Imaginative play

• Symbolic play

• Sensorimotor play

• Object play

• Rough-and-tumble play

Dependent Measures for Studying Play in the Rat

• Contacts directed to nape

• Responses to nape contacts– Responses which tend to continue

the play bout– Responses which either stop the bout

or put the bout “on hold”• Frequency of pins

Contact directed to nape

Response to nape contact

Complete rotation (pin)

The Fun House

Inside the Fun House

Is there a neural circuit for play?

• Experimental approaches

– Lesions

– Metabolic markers

– Administration of neurochemicals

What do we know?

• Cerebral cortex not that important

• Multiple subcortical circuits

– Thalamic / Somatosensory circuit

– Basal ganglia circuit

– Limbic circuit

Thalamic – somatosensory circuitry

• Responsiveness to playful solicitation

• Specificity to stimulus type

• “tickling” and “laughter”

Thalamic – somatosensory circuitry

• Responsiveness to playful solicitation

• Specificity to stimulus type

• “tickling” and “laughter”

Basal ganglia circuitry

• Motor patterning

• Motivational component

• “sensitized” by lack of stimulation (boredom)

Basal ganglia circuitry

• Motor patterning

• Motivational component

• “sensitized” by lack of stimulation (boredom)

Primary motor pathway

Limbic circuitry

• Evolution of mammals and the emergence of limbic system

• Importance of the social bond

Limbic circuitry

• Evolution of mammals and the emergence of limbic system

• Importance of the social bond

Is there a neural circuit for play?

• Multiple circuits

• Cortical development may inhibit subcortical “play circuitry”

Since dopamine seems to be involved in everything else, is it

also involved in play?

CH2CH2NH2

OHHO

“Dopamine, how do I love thee? Let me count the ways”, jokes George Koob, Ph.D., from the Scripps Institute. Excitement about dopamine is now so high that the danger is not underestimating its reach, but exaggerating it:

“Today’s gig is that dopamine is a kind of everyman’s neurotransmitter because it does everything. And the fact is, it doesn’t.

“The Plunge of Pleasure”Psychology TodaySeptember/October 1997

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SN

VTA

PFC

Brain Dopamine Systems

Nigrostriatal systemMesolimbic/Mesocortical system

“Tweeking” receptors with neurochemicals

• Agonists • Antagonists• Reuptake inhibitors• Reverse-reuptake

(release)

Administer drug Observe behavior

Dopamine and play

• Psychomotor stimulants (amphetamine, methyphenidate) potently reduce play

• D1 dopamine agonists and antagonists uniformly reduce play

• D2 dopamine agonists reduce play– Low doses may increase play

• D2 dopamine antagonists uniformly reduce play

• Extensive dopamine lesions alter the patterning of play

Breaking up play

Anticipatory/Preparatory Behaviors

Consummatory Behaviors

Stimuli predictive of reinforcer

Increased release of dopamine in mesolimbic terminal regions

Increased anticipatory or preparatory responding

Anticipatory/Preparatory Behaviors

Anticipatory Response for Play

Control

Play

5 minutes 5 minutes

alone

alone

alone

playpartner

Dependent measure: tunnel crosses

Day of Testing

0 1 2 3 4 5 6 7 8

Tun

nel C

ross

es

0

5

10

15

20

25

30

35

Control (n=9)Play (n=9)

Play experience yields an anticipatory response

Blockade of dopamine receptors with haloperidol

disrupts anticipatory activityTun

nel C

ross

es

0

5

10

15

20

25

30

35

Control Play

VehicleHaloperidol (0.05 mg/kg)

Stimuli predictive of play

Increased release of dopamine in mesolimbic terminal regions

Anticipatory eagerness

Anticipatory Behavior and Play

Ultrasonic vocalizations as measure of anticipatory eagerness

• Control animals placed in chamber for 2 minutes

• Experimental animals placed in chamber for 2 minutes prior to a 5 minute opportunity to play

Acquisition of 55 kHz vocalizations

Haloperidol reduces vocalizations

Effects of haloperidol on play

• Nape contacts reduced in rats allowed to play with same partner every day

• No effects on responsiveness to nape contacts

Since dopamine seems to be involved in everything else, is it

also involved in play?

• Important for actual execution of the behavior patterns

• Anticipatory eagerness• Mesolimbic vs.

nigrostriatal involvement

CH2CH2NH2

OHHO

Are there genes for playfulness?

Use of inbred strains• Known behavioral and neurobiological

differences between selected strains• Fischer-344 and Lewis strains

• Groundwork for studying genetics of play

• Increased understanding of disorders with genetic origins

Fischer-344 and Lewis strains• Responsiveness to stress

• Fischer > Lewis

• Reactivity to handling and novelty• Fischer > Lewis

• Susceptibility to inflammatory disease• Lewis > Fischer

• Self-administration of abused drugs• Lewis > Fischer

• Play behavior• Lewis > Fischer

Play solicitation

Playful responsiveness

Does isolation affect sensitivity to amphetamine?

Fischer or

Lewis

Socialvs.

1 day isolation

Socialvs.

3 days Isolation

60 minutes baseline

Amphetamine (2 mg/kg)

90 minutes post-injection

Amphetamine has comparable effect after 1 day of isolation

3 days of isolation results in sensitized response in Lewis rats, but not Fischer rats

Chronic, intermittent drug taking

Chronic, intermittentbouts of play

withdrawal

isolation

Sensitized responseto amphetamine

Sensitized responseto amphetamine

Drug-induced sensitization

Isolation-induced sensitization

Is there a parallel with drug use and abuse?

Are there genes for playfulness?

• Strain differences

• Independence of maternal influence

• Individual differences?

• Personality traits?

Can studying play in rats tell us anything about psychiatric conditions

in human children?

• Attention deficit disorder (ADHD)

• Autism

• Childhood depression

• Anti-social behaviors and violent tendencies

Is this the “fountain of youth”

Why is it important for your child to play?

When children play, they exercise their senses, their intellect, their emotions, their imagination - keenly andenergetically…to play is to explore, to discover and to experiment. Playing helps children develop ideas and gainexperience. It gives them a wealth of knowledge and information about the world in which they live - andabout themselves. So to play is also to learn. Play is funfor children. But it’s much more than that - it’s good forthem, and it’s necessary…play gives children the opportunityto develop and use the many talents they were born with.

Why is it important for your child to play?

When children play, they exercise their senses, their intellect, their emotions, their imagination - keenly andenergetically…to play is to explore, to discover and to experiment. Playing helps children develop ideas and gainexperience. It gives them a wealth of knowledge and information about the world in which they live - andabout themselves. So to play is also to learn. Play is funfor children. But it’s much more than that - it’s good forthem, and it’s necessary…play gives children the opportunityto develop and use the many talents they were born with.

Lego’s Building Set