Neuroscience of Adolescence Flashcards
Bottom up development
The brain develops from the bottom up, like a stack of building blocks.
The upper block
referred to as the ‘intellectual’ brain
The middle blocks
referred to as the ‘primitive’ brain
The lower block
referred to as the ‘reptilian’ brain
The Reptilian Brain
Developed as simple animals evolved a brain
Mesal aspect of a brain sectioned in the median sagittal plane.
Begins where spinal cord enters the skull
Produces movement and creates a sensory world
Rhombencephalon
Evolutionarily the oldest Cerebellum Reticular Formation Pons Medulla
Cerebellum
Controls complex movements and has a role in a variety of cognitive functions, as well
Size of cerebellum increases with the physical speed and dexterity of a species
Because of its large number of tiny granule cells, the cerebellum contains more than 50% of all neurons in the brain, but it only takes up 10% of total brain volume
Reticular Formation
“Reticular activating system”
Stimulates the forebrain:
Regulation of sleep-wake behavior and behavioral arousal
Pons
(“bridge”)
Connects cerebellum to the rest of the brain
Controls important movements of the body
Medulla
Rostral end of brain
Vital functions:
Control of breathing and heart rate
Non-associative learning
The reptilian brain regulates non-associative learning - a relatively permanent change in the strength of response to a single stimulus due to repeated exposure to that stimulus.
Habituation
the strength or probability of a response diminishes when the response is repeated
Sensitization
the progressive amplification of a response follows repeated administrations of a stimulus
The Primitive Brain
Developed as animals evolved adaptive behaviors
Produces emotions and motivations that enhance the probability of surviving and reproducing
The Primitive Brain
Organize & generate motivated behavior
Motivates behaviors
Homeostatically regulate Behaviors
Learn & predict to guide behavior
The Reptilian Brain
Reflexively controls life processes
Non-associative learning
Subcortical Structures
Mesencephalon
Diencephalon
Limbic System
Basal Ganglia
Mesencephalon
Tectum
Tegmentum
Tectum
Sensory processing
Orienting movements
Tegmentum
Eye and limb movements
Species-specific behaviors
Perception of pain
Diencephalon
Thalamus
Hypothalamus
Thalamus
Relay station
Hypothalamus
Feedback loops via hormones
Neural Control via Oxytocin
Experiential Responses
Medial Forebrain Bundle
Limbic cortex
Cingulate gyrus
Hippocampal formation
Amygdala
Cingulate gyrus
Autonomic functions
Hippocampal formation
Long-term memories
Spatial navigation
Amygdala
Process & associate positive & negative emotions
Basal Ganglia
Caudate nucleus
Putamen
Nucleus accumbens
Globus pallidus
Corpus Striatum
Dorsal Striatum
Ventral Striatum
Ventral Pallidum
Dorsal Striatum
Caudate & Putamen
Procedural/associative learning
Process rewards & punishments
Ventral Striatum
Nucleus accumbens - indicates incentive salience (i.e., wanting)
Ventral Pallidum
Process hedonic value (i.e., liking)
MESOLIMBIC DOPAMINE (DA) SYSTEM
DA projections from the VTA to:
Basal Ganglia
Temporal Lobe
Basal Ganglia
- Learning/predicting in response to rewards/punishments (V. Striatum)
- Indicating hedonic value (Pallidum)
Temporal Lobe
- Processing/associating both positive & negative emotions (Amygdala)
- Rapidly encoding salient features into memory (Hippocampus)
Associative learning
The primitive brain regulates associative learning - the flexible learning of an association between two stimuli, or a behavior and a stimulus
Operant Conditioning
a certain behavior is either reinforced or punished, which alters the probability that the behavior will reoccur
Classical (Pavlovian) Conditioning
a previously neutral stimulus is repeatedly presented, together with a reflex eliciting stimuli, until eventually the neutral stimulus elicits a response on its own
The Primitive Brain
Learn & predict to guide behavior
Review
Limbic system regulates emotions and motivations - particularly those related to survival - such as fear, anger, and pleasure (sex and eating)
Feelings of pleasure/reward are very powerful and self-sustaining
Pleasurable behaviors activate the reward system circuit in the limbic area that is devoted to producing and regulating pleasure
Primitive/ Reptilian Brain
Rapid procedural or habitual learning
Significance
The Primitive/Reptilian Brain facilitates reflexive as well as rapid procedural or habitual (i.e., stimulus-response) learning, which is adept at identifying stimuli and selecting actions based on the predicted outcome.
The VTA, basal ganglia, and temporal lobe are largely sufficient to promote adaptations of motivated behaviors in the face of constantly changing environments and ensure survival.
The Intellectual Brain
Cortex - outer covering; 85% of brain mass
During adolescence, the cortex goes through a major period of growth that helps adolescents transition into adulthood
The Intellectual Brain
Top-down cognitive control of behavior
Frontal Lobe
Motor Cortex
Premotor Cortex
Prefrontal Cortex
Motor Cortex
Controls fine movements
Premotor Cortex
Selection of appropriate movement sequences
Prefrontal Cortex
Involved in specifying the goals toward which movement should be made
Top-down cognitive control of behavior
Prefrontal cortex plans movements
Premotor cortex organizes movement sequences
Motor cortex produces specific movements
Prefrontal Inputs
Receives connections from amygdala, thalamus, posterior parietal (sensory association) cortex, and DA cells of the VTA
Prefrontal Outputs
Projects to amygdala and hypothalamus (inferior) and to posterior parietal cortex, cingulate cortex, basal ganglia, and premotor cortex (dorsolateral)
The Intellectual Brain
Top-down cognitive control of Behavior
Review
The PFC regulates executive functions:
Ability to differentiate among conflicting thoughts, determine good and bad, better and best, same and different, future consequences of current activities, working toward a defined goal, prediction of outcomes, expectation based on actions, and social “control” (the ability to suppress urges that, if not suppressed, could lead to socially unacceptable outcomes)
Ability to adapt behavior appropriately to the environmental context
The Intellectual Brain
Significance
The PFC integrates across all modalities – providing top-down cognitive control while extracting relevant information from these and other structures, translating between different reference frames, as necessary, and amplifying or overriding motivational and affective signals - to predict probable outcomes, coordinate behavior, and select an action based on these probabilities.
In contrast to associative learning mediated by the striatum, the PFC modulates action selection, integrating experiences and predicting both expected and unexpected outcomes before updating stimulus-response associations and selecting an action.
The Neuroscience of Adolescence
- Bottom-up Development
- Nature Saves the Best for Last
- Correlating Brain Development with Behavior
Nature Saves the Best for Last
the PFC is one of the last areas to mature
Synaptic Pruning in the PFC
Following a growth spurt of gray matter that completes around age 11, the PFC goes through a protracted period of synaptic pruning that continues into early adulthood.
Lose ~3% of gray matter in frontal lobes
Myelination in the PFC
Closely following the pruning process, myelin is added to the remaining connections
Allows for more efficient communication
Continues until early 30’s
MESOCORTICAL DOPAMINE (DA) SYSTEM
DA projections from the VTA to:
Frontal Lobe
Modulates associative learning (PFC)
PFC also:
Receives Temporal Lobe Inputs
Provide important learning signals
Projects to Limbic System
Amplifying or overriding motivational and affective signals
Review
Both regressive and progressive processes are occurring in parallel, enhancing neural and cognitive processes.
RESULT: teens move from concrete to abstract thinking…tend to become idealistic and cause-oriented
How does Regional Brain Development Map onto Behavioral Development
Hallmark of behavioral development is a functional gain in ability to suppress an inappropriate action in favor of an appropriate one (impulse control)
Neurobiological Imbalance
Differential development of subcortical relative to prefrontal control regions may explain:
High Risk Behaviors
Emotional Susceptibility
Psychiatric Vulnerability
High Risk Behaviors
Risk-taking declines between adolescence and adulthood because of changes in the brain’s cognitive control system – changes which improve individuals’ capacity for self-regulation.
Developmental Differences in Response to Rewarding Events
Accumbens activity is correlated with risky behavior
Adolescents are similar to adults in volume of accumbens activity
BUT similar to children in PFC activity
Emotional Susceptibility
Exaggerated emotional reactivity declines between adolescence and adulthood because of strengthening of functional connections between the PFC and amygdala
Hormonal Changes are Linked to Emotionality
The presence of testosterone and estrogen both affect the development of the brain
Can alter:
Number of neurons
Dendritic branching
Synaptic growth
Not just areas of brain related to sexual behavior: These hormones can affect “higher functions” such as cognition
Developmental Differences of Emotionality
Functional connectivity between orbital PFC & Amygdala is associated with regulating emotional reactions
Adolescents are similar to adults in volume of accumbens activity
BUT similar to children in PFC activity
Psychiatric Vulnerability
Many mental health disorders first present during adolescence, and may lead to poor school performance, school dropout, strained family relationships, involvement with the child welfare or juvenile justice systems, substance abuse, and risky sexual behaviors.
Correlating Brain Development with Behavior
Increased risking taking behavior in adolescence may be related to differential development of limbic subcortical vs. cortical control regions.
Developmental changes may be exacerbated by individual differences in tendency to engage in risky behavior.
Exaggerated emotionalreactivity declines between adolescence and adulthood because of strengthening of functional connections between the PFC and amygdala
Individual differences in responses to positive or negative events may put certain teens at risk for poor outcomes
The still developing PFC may be especially vulnerable to environmental factors that increase risk for psychiatric disorders
Genetic differences and how teens spend their time influences both the organization and the capacity of the brain
Significance
“USE IT OR LOSE IT”
Brain connections that are stimulated and used repeatedly grow stronger while unused connections wither away.
How teens spend their time is CRUCIAL to brain development since their activities guide the structure of the brain
