Chapter 2 - The Adolescent Brain: A work in Progress

List the behavioural and cognitive functions of the prefrontal cortex.

- Controlling impulses - Inhibiting inappropriate behaviour - Initiating appropriate behaviour - Stopping an activity upon completion - Shifting / adjusting behavior when situations change - Providing a temporary mental workspace for working memory - Organizing things - Forming strategies and planning behaviour - Setting priorities among tasks and goals - Making decisions - Empathy - Sensitivity to feedback (reward and punishment) - Insight

What forces guide the building up or pruning down of the connections between cells?

- Scientists do not yet understand all of the forces that guide the building up or pruning down of connections between cells. Both are likely influenced by genetic and environmental factors. ie) roles of bacteria, viruses, nutrition, education, parenting, school, peers, drugs, video games and many other factors. - The best hypothesis at present is that learning and the formation of memories guide the building-up of connections. The best current hypothesis at present to explain the pruning phase is the "use it or lose it" principle; that is, those cells and connections that are used will survive and flourish; those that are not used will whither and die

What is the "gambler's fallacy"?

- a belief that the next event in a series of events will compensate for a prior sequence in which an outcome occurred with greater-than-expected frequency - ie) after a coin toss yields heads 15 times in a row, the gambler's fallacy would result in a belief that there is a greater than 50-50 chance that the next toss will yield tails, despite the fact that each coin toss is independent and the probability of either outcomes is .50

What happens to the connection between the cingulate and the hippocampus during adolescence?

- cingulate, an area of the brain involved in emotions, and the hippocampus,a memory hub - The cingulate connects to the brain stem and spinal cord, modulating our physical reactions to emotions such as sweaty palms, increased heart rate, and that tense feeling in our stomach. The hippocampus helps retrieve memories, to put situations in historical context, and to remember past details about a situation that might be important. - A myelin-covered bridge of axons called the superior medullary lamina connects these two areas. The laying down of myelin in this circuit is one of the most active processes in all the brain, with the myelin content doubling during the teen years

What often happens to adults whose frontal lobes are damaged?

- lack "inhibitory control;" that is, they tend to be somewhat uninhibited and impulsive - ie) Phineas Gage, a 25-year-old Vermont railroad foreman who suffered a brain injury in l848. While packing down blasting powder, he inadvertently sparked an explosion that sent a 1.25" diameter tamping iron, more than a yard long, rocketing through the bottom of his left cheek bone and out through the top of his head. The formerly diligent, responsible foreman became a person who was extremely impulsive, ill mannered and unable to follow through on his obligations. "Gage was no longer Gage," said one of his friend

Explain why it might be more difficult for young adolescents to control impulsive behaviour or inhibit inappropriate behaviour?

- the adolescent brain functions relatively inefficiently on selected inhibitory tasks. - Although the teen brain expends a great deal of effort while performing working memory tasks involving inhibition, it fails to fully engage the neural structures, as reflected in a greater number of errors on the task - Such inefficient "thinking machinery" may make young adolescents more susceptible to being distracted. - If neural networks responsible for the complex cognitive processing demands of inhibitory and impulse control are not yet physiologically mature, the teen brain may struggle when it is necessary to control impulsive behavior or inhibit inappropriate behavior and stay focused on a current task or situation.

Approximately how many neuronal connections are formed in the human brain by the end of adolescence?

By the end of adolescence, the human brain, the most complicated three-pound mass of matter in the known universe, contains over 10 billion neurons and another 100 billion support cells. The 10 billion neurons form over 100 trillion connections with each other—more than all of the Internet connections in the world!

What type of neurons do drugs such as cocaine and amphetamines target? How might these drugs affect brain development?

Drugs such as cocaine and amphetamine target dopamine neurons, and damage to these very neurons caused by such drugs might affect adolescent brain development, especially the brain's ability to experience reward and learn from it throughout adult life

What is the "critical period" for developing normal vision?

First 2 years of life

What type of synapses experience the greatest loss during pruning?

From birth to early adulthood, most of the pruning, or loss, of synapses involves excitatory synapse

What happens to the surface of the brain from birth to adulthood?

In addition to doubling in size, the brain's surface folds become much more complicated. Evidence suggests that this increasingly complex folding may be related to the elaboration of underlying connections among cells. The complexity of the folding patterns becomes increasingly obvious in parts of the brain cortex—the outer mantle—that process cognitive and emotional information (as distinct from parts of the brain responsible for the control of more basic motor and sensory functions)

When do the 2 bouts of "pruning" occur?

In humans, a second bout of overproduction of connections occurs just before puberty, followed by "use-it-or-lose-it" pruning through the teen years, as connections are shaped and refined.

Describe the synaptic "pruning" process

In the earliest stages of brain development, primarily before birth, there are many more brain cells and connections formed than can possibly survive. A process of competitive elimination, or "pruning," follows this vast overproduction. Those cells and connections that are used survive; those that aren't used wither. This process occurs in all species possessing a central nervous system.

What is the function of myelin?

Protects and electrically insulates axon. Increases speed of nerve impulse transmission (up to 100-fold compared to axons lacking myelin.)

What are the functions of the amygdala and how does it change during adolescence?

The amygdala processes emotional information, especially the experience of fear, danger and threat in the environment.

What area of the brain is not fully myelinated until well into the third decade of life?

The cabling of the prefrontal cortex and related regions, however, is not fully myelinated until well into the third decade of life

What are the functions of the caudate nucleus and how does it change during adolescence?

The caudate nucleus is a relay station for information destined for the prefrontal cortex, and seems to be important for learning to make certain behavioral routines more or less automatic.

What are the functions of the hippocampus and how does it change during adolescence?

The hippocampus is critical to the formation of new memories, and studies in human brain and in nonhuman primates indicate that changes in the hippocampus's synaptic organization, dopamine wiring, and myelination also occur during adolescence.

What is myelin?

The long extensions that allow neurons to span many centimeters from one brain region to another are called axons. These fibers connect the body of the cell—the nucleus with it DNA and the protein synthesis machinery—to the distant terminals where chemical signals are sent via synapses to the dendrites of other cells. Since axons must conduct electrical impulses over relatively long distances, they are wrapped in a fatty chemical coat called myelin

Why is recovery from stroke and head injury more difficult later in childhood?

The plasticity of the child's brain is reflected in the fact that damage to it—for example, through a stroke or head injury—can often be compensated for, since so many extra synapses are available to help out and take over for the damaged cells Later in childhood, after the period of exuberant overproduction of connections, recovery is much more difficult, because the potential for a cell to find an alternative wiring diagram is more limited.

What did researchers discover about early adolescents' and adults' working memories when they were asked to solve a complex problem?

The prefrontal cortex is not yet mature or especially efficient during adolescence. This suggests that, as a group, teens may not always possess the cognitive workspace —the working memory—necessary for solid planning of complex behaviour

What has dopamine been found to be critical for?

This chemical has been found to be critical for focusing attention on environmental stimuli when it is necessary to choose between conflicting options, especially when the goal may not be obvious and choices based on memory, not impulse, are required.

While undergoing fMRIs, adolescents and adults were asked to identify the emotions in people's faces. What area of the brain was activated in teens and adults?

When trying to identify the emotions expressed by the faces, the teens activated their amygdala, which, as noted above, is involved in the primal assessment of fear. By contrast, adults activated the frontal lobes when performing the same task and were better able to correctly identify the emotions expressed on the faces.