Lecture 1: A neuroscientific perspective on
adolescent development
How do we study the brain?
- Behavioral experiments (Reaction times, behavior)
- Patient studies
- Pharmacological studies
- Animal studies
- Neuroimaging techniques: PET (positron emission topography), TMS
(transcranial magnetic stimulation), tDCS (transcranial direct current
stimulation), DTI (Diffusion tensor imaging), MEG
(magnetoencephalography), EEG (electroencephalography) (f)MRI
((functional) magnetic resonance imaging)
Brain development
The neuronal cell bodies are what forms the gray matter. If a child has more cells
than an adult that means that grey matter decreases with age. One of the biggest
changes that take place after birth are more and more connections are being made
between different brain cells. These connections are what forms white matter,
thus there is going to be increasing amounts of white matter with age. There is also
an increasing course of myelination of the cortex with age (smooth transaction of
information across neurons).
White matter
Linear increase until young adulthood : more myelination and more connections
between the neurons with increasing age
Gray matter development
Non-linear decrease until young adulthood:
1. Synaptogenesis: increase in the number of neurons and synapses between
the neurons. However, this does not keep on increasing.
2. Pruning: elimination of excess synapses
The decrease in gray matter is not the same for all brain regions and it does not
happen all at once. The structural change takes longer in the prefrontal and
temporal lobes.
MRI
Magnetic resonance imaging: measures brain structure
,fMRI
Functional magnetic resonance imaging: measures brain function/activity. It
measures increased blood flow (= more oxygen = more activity): BOLD-effect
(Blood Oxygenation Level Dependent). Changing hemoglobine in red blood cells;
magnetic properties of hemoglobine is measurable
Important to keep in mind:
● BOLD signal is not an absolute measure of brain activation but relative
● Control condition is thus crucial
● Many trials per condition (>20)
● Fixation between trials
● Engage participants
fMRI vs EEG
fMRI & EEG: both non-invasive techniques
Fmri has high spatial resolution, the active parts of the brain are easily
distinguishable and differences between activity in brain areas are easily observed.
However, it has a low temporal resolution, meaning that the signal takes a while to
be detected. This happens because it is an indirect measure
EEG has high temporal resolution (language/speech production). Because the
signals collected with EEG are derived from the surface of the brain, EEG’s spatial
resolution is limited. Activation during long periods of time is possible, because
collecting data over longer periods of time is easier with EEG than fMRI.
Understanding adolescence
Adolescence is the transition period between childhood and adulthood. It is
associated with the start of hormonal changes in the body (puberty). Adolescence is
also culturally determined.
,Social information processing Network (article 1)
Focus on understanding the dramatic changes in social behavior in adolescence
(social reorientation).
The model of social information processing suggests that we can talk about the
brain in terms of 3 different nodes (detection, affective, cognitive-regulation
nodes). Whenever one is in a social situation there are different steps that the brain
goes through.
1. Some of these happen automatically, without even taking notice in them.
This is the detection node. This is the first level of information processing,
perceptual processing (face perception, expressions, biological motion, other
sensory modes). These are proceeds that happen very quickly. Fusiform area
and other regions in the temporal lobe are important for the processes
related to the detection of social information
2. The second level of processing occurs at the affective node that is responsible
for emotional responses. The subcortical structures of the brain are mainly
important (striatum, amygdala, nucleus accumbens, insula). Anything related
to emotions, including positive and negative emotional arousal, approach and
avoidance and rewards.
- positive /negative emotional arousal (amygdala)
- Negative emotions like disgust, fear, unfairness (insula)
- Reward (nucleus accumbens/striatum)
3. The cognition/regulation node is associated mainly with the prefrontal cortex
and it has to do with regulating decisions, monitoring perception and
affection as well as memory
- self-referential processing, self reflection, mentalizing [medial
prefrontal cortex (mPFC)]
- Behavioral control, working memory [dorsal lateral PFC (dlPFC)]
- monitoring of affective state / action [anterior cingulate cortex (ACC)]
There are different times in which those three nodes develop.
Detection node: early maturation
Affective node: maturation in early adolescence
Cognitive node: maturation in late adolescence
When it comes to the affective node, some brain changes appear to be the
consequence of pubertal hormones. The hormonal changes seem to have direct
relationships with the subcortical brain regions and their development. There is a
general functional and anatomical reorganization of the affective node during
puberty.
- gonadal hormones (e.g., estradiol, testosterone) are related to how affective
node structures respond to social stimuli
, - many neurotransmitters involved in social behavior (dopamine, serotonin,
oxytocin, vasopressin) regulated by gonadal steroids; e.g. estrogen levels
can increase oxytocin receptor density in the amygdala and nucleus
accumbens, which are related to nurturant behavior
- heightened emotional responsiveness to affective stimuli, especially in
particular contexts (e.g. the peer context)
The development of the cognitive node appears to be independent of pubertal
processes. The maturation of the cognitive node happens towards late adolescence.
- PFC (including OFC, VLPFC, DLPFC, mPFC) do not reach maturity until early
adulthood
- performance on inhibitory tasks improves until late adolescence
- this development is independent of hormonal status (and is related to
myelination and pruning)
There is a slow maturing prefrontal cortex and
regulatory node and there is an overactive
affective node which matures in high speed in
early adolescence, related to pubertal hormones.
Dual-system model or Imbalance model is a
neurological model of adolescent brain
development. The prefrontal regions develop with
age across adolescence and they develop slowly.
The limbic/subcortical regions show a speeded
development with puberty (due to hormonal
changes). Thus, these regions become sensitive
and get activated more easily. The brain regions
that are important for reward and information processing belong to different nodes,
which leads to an imbalance of the whole system.
More recent models
suggest that with
increasing age whereas the
prefrontal regions follow
their course of
development with age,
with puberty a peak is
visible in emotional
reactivity and their related
brain regions. This leads to
a gap between the two
nodes.
,Role of motivation
Recent neuroimaging evidence does not support a simple model of frontal cortical
immaturity. There is evidence in the idea that it is important for the tasks to
measure cognitive control or affect in the experimental design, because this
crucially influences the results from the brain scans. Growing evidence for
importance of social-affective processing (role of motivational salience of the
context).
Cognitive control
The motivational salience of the task used in studies significantly influenced the
results. It seems that the context modulates the results to a great degree.
- Motivation (social/contextual) can modulate cognitive control (rewards can
improve performance)
- Control can suffer when required to suppress action towards reward
,Article 1: The social reorientation of adolescence: a
neuroscience perspective on the process and its relation
to psychopathology.
During adolescence dramatic changes happen in social behavior. The social brain undergoes
many changes during adolescence. Research shows that changes in social behaviour are
caused by sociocultural factors and innate characteristics. Both ensure that the brain adjusts
naturally on a social level. In addition, abnormal emotional responses to social situations are
also important for mood and anxiety disorders during adolescence.
Early detection and categorization of stimuli as ‘social’ is followed by neuronal processing
that then integrates the stimulus into a larger and cognitive framework.
This process involves bi-directional interactions between areas devoted to:
- social detection
- affective processing (limbic regions)
- Higher order cognitive processing (prefrontal cortical regions)
The Social InformationProcessing Network
The Social InformationProcessing Network (SIPN) is broken down into three basic nodes
based on the similarity of function and developmental timing.
1. Detection node: categorizing a stimulus as social and dividing it into its basic social
properties. It includes
- Inferior occipital cortex
- Inferior regions of the temporal cortex
- Interparietal sulus
- A region in the fusiform gyrus known as the fusiform face area
- Superior r temporal sulcus (STS): involved in the processing of biological
movement
- Areas in the anterior portion of the temporal cortex: implicated in social
recognition
These regions together carry out perceptual functions. For example determining
whether a stimulus is moving or not, whether it belongs to the same species or not
(conspecific), and what its individual identity is.
2. Affective node: Once a stimulus has been categorized as social and its basic
properties are identified, it is processed in the affective node. The affective node is
composed primarily of regions engaged by reward or punishment. These include
- Amygdala
- Ventral Striatum
- Septum
- Bed nucleus of the stria terminalis
- Hypothalamus
- Orbitofrontal cortex (under some conditions)
This node also modulates various autonomic and cognitive processes such as
cardiovascular control and attention allocation, in order to organize the systematic
response to social stimuli. Several regions in the affective node have been found to
, display increased activity in adults when emotionally provocative social stimuli were
shown (their romantic partners/children/erotic stimuli/fearful or threatening
expressions)
3. Cognitive-regulatory node: Three basic processes occur in the cognitive-regulatory
node.
- Theory of Mind (TOM) processes: driven largely by activity within the
paracingulate area or dorsomedial prefrontal cortex
- Inhibition of prepotent responses: regulated by the ventral prefrontal cortex
- Generation of goal-directed behaviors: relies on interactions between the
dorsal and ventral prefrontal cortices
The cognitive-regulatory node comprises the medial and dorsal prefrontal frontal
cortex and portions of the ventral prefrontal cortex, including the orbitofrontal cortex
The SIPN model assumes that the aforementioned processes take place one after the other.
However, when looking at the brain, one can see that the three processes are part of an
interactive network. For example, the detection areas receive information from the affection
areas to be able to interpret a stimulus as social.The three nodes don’t work in isolation but
they function as an interactive network.
Changes in the SIPN during adolescence
There are many changes in social behaviour during adolescence. Three major changes are
sexuality, being more focused on peers and less focused on parents. These changes are not
unique to humans but are a universal phenomenon among socially living species.
Detection node
The ability to perform categorical and perceptual processes on social stimuli using the
detection node of the SIPN matures well before adolescence, and, to our knowledge, no
, changes in this node have been documented during the adolescent period, since the
structures are already mature.
Affective node
During puberty, there are both functional and anatomical changes in the regions that make
up the affective node. Gonadal steroids alter brain function in a variety of ways,
- To regulate other neurotransmitter systems. Neurotransmitters that are involved in
social responsiveness are: dopamine, serotonin endogenous opioids, oxytocin, and
vasopressin.
- They are involved in behavioural changes in social responses. In both males and
females, higher levels of androgen in circulation result in increased capacity of a
social stimulus to elicit urges for sexual approach
- Studies find links between sex hormones and sexual behaviour, parental behaviour,
social bonding and social memory.
- Studies have also shown that hormonal effects are most important during initial
encounters with a novel stimulus, and after behavioral patterns have been
established they become relatively independent of hormonal manipulations. The
adolescent period may be a particularly important and malleable one in establishing
patterns of social behavior.
- Functional changes in the areas of the brain related to affection have an effect on the
amount of sex hormone that is released.
Cognitive-regulation node
People with damage to the prefrontal cortex have problems with social awareness and
making social decisions. The earlier in development these areas are damaged, the more
intense the effects are. Portions of the prefrontal cortex, including orbitofrontal,
ventrolateral, and medial prefrontal regions, do not reach maturity until early adulthood,
typically in the late teens or early twenties. Thus, this means that for example, inhibition
control is very difficult for younger people, which is related to both functional and
morphometric development in the prefrontal cortex. The development that does occur in the
cognitive node is a result of increased myelination and pruning of existing synaptic
networks. This developmental process occurs throughout the brain but is protracted in the
prefrontal regions. Developmental changes within the cognitive node are likely to be slow,
iterative, and independent of hormonal status. Interaction with the affective areas can,
however, ensure that hormone levels play a secondary role in the changes in the brain
involved in cognitive regulation.
Neuroimaging techniques and changes in the SIPN Model
The central nervous system mediates changes in the social brain areas during adolescence.
Very little is known about which changes are taking place within the areas as discussed in
the SIPN model.
For example, a recent study from our laboratory highlights differences between adolescents
and young adults in activation patterns in both the affective and the cognitive-regulatory
nodes while processing social stimuli. While passively viewing faces with fearful emotional
expressions, adolescents exhibited greater activation than adults in the amygdala,
orbitofrontal cortex, and anterior cingulate. This finding suggests that when attention is
