1
Q
What is biopsychology?
A
The scientific study of the biology of behaviour.
An integrative field of study that is still young, but a rapidly growing science.
2
Q
What are the types of research in biopsychology?
A
- Pure/basic research: the foundation of research, motivated by desire to understand how things work.
- Applied research: trying to come up with some kind of solution, provides better understanding.
3
Q
Describe the Coolidge Effect
A
A copulating male that becomes incapable of continuing to copulate with one female can often recommence with a new female. Females are more receptive towards a new male.
Tested in 3 Stages (with hamsters)
- Female copulated with 1 male until he is tired
- All females receive a new male and continue copulating
- All females receive a 3rd male (half get the SAME male as in phase 1, half get a NEW male who was with a different female in phase 1)
4
Q
What are the advantages and disadvantages of animal studies?
A
Advantages:
- less complicated
- simpler brains, more direct analysis
- fewer ethical restrictions
Disadvantages:
- need for validation, need to be careful about generalizations about humans based on observations
5
Q
What are the advantages and disadvantages of human studies?
A
Advantages:
- verbal communication
- generalizability is less of an issue
- humans can follow instructions
- can report subjective experiences
- cheaper than animals
Disadvantages:
- greater ethical constrains, restricts use of more invasive experiments
6
Q
Describe the case of Jimmie G and Korsakoff’s Syndrome
A
1975 - A 49 year old man who cannot form new memories, and has short term memory that only lasts a few minutes (anterograde amnesia), due to alcoholism.
Korsakoff’s Syndrome, common in alcoholics due to lack of Thiamine (Vitamin B1).
Treatment: doses of thiamine, doesn’t reverse damage but it prevents further damage.
7
Q
Why do certain behaviours persist?
A
Behaviours have some form of evolutionary advantage, or else they would have been weeded out over time.
Adaptive behaviours is maintained; maladaptive behaviour is not.
8
Q
Nature and Nurture
A
- Always nature AND nurture (one can be more dominant than the other in different situations)
- genes expression is influenced by nature and nurture
9
Q
What is fitness? What are the different types of fitness?
A
The ability of an organism to survive and contribute its genes to the next generation.
Direct fitness: genes that are directly deriving from mother/father that are passed on to offspring.
Inclusive fitness: less obvious; portion of genes that are shared between ALL relatives.
10
Q
Describe the comparative method:
A
Studies precursors - relatives that come from a common ancestor (ex. humans and primates).
11
Q
Give an example of evolution being observed in progress
A
Darwin’s Finches - Galapagos islands:
1997 was a summer of severe drought, and big seeds were left. The average beak size of birds increased, as birds with smaller beaks died off since they weren’t able to feed themselves.
12
Q
Describe evolution
A
The idea that species change and adapt and change over time.
Divergent evolution: presumably evolved from a common ancestor with different functions (ex. human arms and bird wings).
Convergent evolution: evolved from different origins that have similar structure and functions (ex. bird wings and insect wings).
13
Q
Describe Darwin’s observations and deductions
A
- Organisms have an enormous capacity to overproduce, but populations remain remarkably stable. This means there is a struggle for survival.
- Individuals differ in their characteristics, and many of these differences are heritable. This means that those individuals who possess adaptive characteristics will reproduce more successfully than those who don’t and will pass these characteristics on to their offspring. This is what Darwin meant by “natural selection”.
14
Q
Spandrels
A
Evolutionary byproducts that don’t seem to have and particular function/significance, can assume an adaptive function over time (ex. bellybutton).
15
Q
When does reciprocal altruism occur?
A
When there is:
- individual recognition (need to be able to find each other again)
- long-lived individuals
- stable communities
- well-developed memory (need to remember what happened)
16
Q
Structural Genes
A
- main genes for coding proteins
- turned on and off by operator/promotor genes
- bound by transcription factors that increase/decrease the likelihood of the gene being expressed
17
Q
Operator Genes
A
- control one or more structural genes
18
Q
Describe the process of gene expression
A
- DNA opens
- Transcription occurs
- RNA is synthesized (uracil instead of thymine, single stranded)
- mRNA (messenger RNA) is produced
19
Q
Micro and other regulatory RNAs
A
- short
- bind to mRNAs with complementary sequences and affect their translation to proteins
- seem to be able to inhibit transcription
- gene silencing
20
Q
Epigenetic effects of parental care
A
More physical contact with offspring (in many species) is associated with higher quality of life and more well adjusted adults, who experience lower levels of anxiety.
Over multiple generations (nongenomic transmissions).
Mouse Example:
High maternal care
(lots of licking and grooming) leads to de-methylation of genes involved in the control of stress responses, equalling lower stress hormones and lower anxiety.
21
Q
What are examples of histone modifications and what do they do?
A
Modifications:
- phosphorylation
- acetylation
- methylation
They regulate chromatin opening
- open chromatin: transcriptional activation
- closed chromatin: transcriptional repression
Modifications change access to DNA.
22
Q
Seasonal brain plasticity: black-capped chickadees
A
- food storing birds who store food in autumn
- recover stored food in winter
- their hippocampus is analogous which is very important as the bird needs to remember where the food is stored (need cognitive maps)
23
Q
Birdsong development:
A
Sensory phase: listen to and memorize the adult’s song.
Sensorimotor phase: practice; twitter/sub-songs - perfect it so that it sounds like adult’s song in memory.
Some birds are age limited learners and must learn songs by adulthood, when they become unchangeable (ex. zebra finch), while others are open-ended learners and can improvise and personalize songs over their lifetimes (ex. canary).
24
Q
Synaptic transmission
A
Chemical transmission of signal from one neuron to another. Important that signal is released at the appropriate time, as well as deactivated at the appropriate time.
25
Common types of synapses
- Axodendritic (axon-dendrites)
- Axosomatic (axon-cell body)
- dendrodendritic (dendrite-dendrite)
- axoaxonal (axon-axon)
26
Properties of electrical synapses
- gap junctions: membrane coupling
- free transit of small molecules and ions
- passive spread of depolarization
27
Neurotransmitters
Chemicals that act as messengers between cells in the nervous system; they transmit impulses across the synaptic cleft from a neuron to another neuron, a muscle, a gland...
Many neurons synthesize and release one neurotransmitter, but there is often coexistence between multiple transmitters.
- amino acids
- monoamines (catecholines, indolamines)
- acetylcholine
- unconventional neurotransmitters (soluble gases, endocannabinoids)
- neuropeptides
28
Release of neurotransmitters
1. the action potential reaches the synaptic terminal
2. voltage-activated calcium channels open
3. calcium ion influx
4. presynaptic vesicles fuse (dock) with the cell membrane
5. release neurotransmitter in the synaptic cleft
6. exocytosis
29
Termination of synaptic activity occurs when:
1. Reuptake occurs: cells recycle
| 2. Enzymatic degradation occurs
30
Deliberate genetic manipulations
Gene knockout and gene knockin:
- global gene expression
- spatially limited gene expression
- temporarily limited gene expression
31
Agonist drugs
A drug that facilitates the effects of a particular neurotransmitter.
Either enhances or mimics the effects of a neurotransmitter.
32
Antagonist drugs
A drug that inhibits the effects of a neurotransmitter.
Inhibit or attenuate the effects of a neurotransmitter, usually causes an impaired effect on behaviour.
33
7 Steps in Neurotransmitter Action
1. Synthesis
2. Storage in vesicles
3. Degrading enzymes control "leakage" from vesicles
4. Release
5. Receptor binding - autoreceptors
6. Receptor binding - post-synaptic receptors
7. Termination
34
Competitive binding
Compete for binding site on the receptor.
35
Non-competitive binding
Drugs or other endogenous ligands.
36
What happens when cells fire too rapidly?
They burn out and die.
37
What is a function of glutamine?
Glutamine safely stores glutamate until more is needed.
38
Gluatmate
- excitatory amino acid neurotransmitter
- produced in many neurons throughout the brain
- 4 receptors (NMDA, AMPA, Kainate, Metabotropic Glutamate receptor)
39
NMDA receptor
- Involved in the formation of memories
40
Hebb's Postulate
Synaptic plasticity.
| Essentially "cells that fire together wire together".
41
Long-term potentiation (LTP)
An ENDURING change in communication between pre and post synaptic cells in response to salient stimulation (including behavioural)...
Synapses are effectively made stronger by repeated stimulation.
42
NMDA receptor subtypes
- receptor proteins
- different combinations create different versions of NMDA receptors
- NR2B receptors are more sensitive, and more prevalent in developing brains, less prevalent in aging brains
- NR1 receptors are found in ALL receptor subtypes, necessary for NMDA receptor to work properly. Removal impair hippocampal performance, which impacts memory.
43
NR1 subunit CA1-KO mice
- NR1 subunit in CA1 is needed to produce LTP
44
NR2B overexpression - the "Doogie" mouse
- overexpression through a gene knockin in the forebrain
- enhances LTP
- enhanced spatial learning
- enhanced object memory
45
GABA
- inhibitory amino acid neurotransmitter; inhibitory effects are crucial for normal brain functions
- there is a delicate balance between excitation and inhibition; too much excitation can lead to seizures and convulsions
- 2 types of receptors GABAa (ionotropic) & GABAb (metabotropic)
- orthosteric binding site
46
Benzodiazapines
Anxiolytic; muscle relaxing; anti-convulsant; impair learning and memory; boost the effects of GABA when they bind, don't really do anything on their own
47
Barbiturates
Calming in low doses; anesthesia (higher doses); impair learning and memory
48
Steroids
Calming
49
Alcohol
Regulates GABAa funciton
50
Monoamine neurotransmitters
Localized synthesis in the brain stem nuclei, widespread functions.
Enzymes that are expressed determine where the reaction stops.
51
Dopamine
- synthesis in the mesencephalon (midbrain)
| - dopaminergic cell bodies are typically found in the substantia nigra
52
Substantia nigra
- in the striatum
- nigrostriatal pathway
- Parkinson's disease is associated with death of cells in the substantia nigra
53
Ventral Tegmental Area (VTA)
- located in the limbic system (mesolimbic pathway) and prefrontal cortex (mesocortical pathway)
- important for reinforcing effects, central to the reward system in the brain (food, water, sex, drugs, alcohol)
54
L-DOPA
Administered instead of dopamine in the treatment of Parkinson's Disease because it is able to penetrate the blood-brain barrier.
- increases the rate of synthesis in the remaining cells
- limited efficacy because of schizophrenia-like side effects (confusion, anxiety, hallucinations)
55
Serotonin
Important neurotransmitter that has implications in:
- mood disorders
- aggression
- feeding
- sleep
Synthesis occurs in the midbrain, pons, and medulla; mainly in the neurons of the raphe nuclei.
At least 18 different receptors.
56
Acetylcholine
- receptors are cholinergic and nicotinic
- first neurotransmitter discovered, very abundant in the brain and periphery
- involved in muscular contraction in muscular junctions
- regulates sleep, learning, memory...
- cholinergic cells in the brain are the first and most affected by Alzheimer's
57
Botulinum Toxin (Botox)
- antagonist, but doesn't lock the receptor; instead it prevents the release of ACh
- cleaves the snare protein so that docking can't occur, meaning exocytosis can't occur
- when ACh isn't released, muscles can't contract, which leads to paralysis death from respiratory depression
- can be used for therapy in VERY small doses and in localized manners
58
Muscarinic receptors
- metabotropic
- exogenous substances that act directly on cholinergic receptors
- compete with ACh for binding access
59
Nicotinic receptors
- ionotropic
| - ACh and antagonists acting on nicotinic receptors in the brain can enhance memory and attention
60
What are the 2 classes of amnesia?
1. Retrograde (backward-acting): unable to remember the past. Very strong in recently acquired information, while older information is less affected.
2. Anterograde (forward-acting): unable to form new memories. Usually occurs at the beginning of a disease, or is caused by severe trauma to the head.
61
What is infantile amnesia?
- childhood events are forgotten
| - explicit forgetting occurs more rapidly than implicit forgetting
62
What are the 2 types of memory?
1. Explicit, or declarative memory (conscious): explainable things
- episodic (autobiographical, ex. personal events, experiences)
- semantic (general information, ex. facts, use of language, writing, general knowledge)
2. Implicit memory (unconscious): things that can't be explained as easily; habits and skills that are the result of extensive practice/non-conscious practice
- procedural (skills and habits, ex. riding a bike)
63
Describe the case of H.M. and the contributions it made to scientific research
- a 27 year old man who experienced severe epileptic seizures; had his temporal lobes removed
- his seizures were reduced, but so was his long-term memory
- he had mild retrograde amnesia
- multiple tests such as digit span test, block-taping memory-span test, mirror drawing test, incomplete picture test, and pavlovian conditioning were used to assess H.M.
- showed that medial temporal lobes are involved in memory
- short term memory and long term memory are distinctly separate
- explicit vs. implicit memory are separate too
64
Medial temporal lobe (MTL) amnesia
- many patients are not able to form new explicit long-term memories (like H.M.)
- semantic memory may function normally while episodic memory dies (they are able to learn facts, but do not remember doing so)
- MTL amnesiacs may have trouble imagining future events
65
Describe the proposed hierarchical organization of object representations in the ventral visual stream
Different features of an object are separate (A, B, C, D), then they come together in simple combinations (AB, CD), then finally as one to create a representation of an object (ABCD).
The adjacent cortex is very important in object recognition/identification.
Perirhinal cortex is key in object processing and perceiving, but the area is not exclusively visual (receives information from other areas), but it is highly specialized for representing objects.
66
Describe the radial arm maze
This is a foraging task that is used to look at working memory. Rats are usually food deprived for a few hours before the task, so they are motivated to find the food, and they know that there is food to look for.
Food is placed in the arms of the maze, and working memory is assessed by how well the rats locate the food and determine patterns.
67
Describe the Morris Water Maze and the use of alloentric vs. egocentric cues
- this is a very hippocampus dependent task
| - tasks are run so that the mice/rats can't use an egocentric strategy
68
Egocentric spatial memory
Navigating according to your position in space (don't necessarily need visual cues, more a sense of direction with regards to your body [left, right, forward, backward]).
69
Allocentric spatial memory
Navigating according to landmarks (visual). The hippocampus is specialized in allocentric spatial memory/processing.
70
What are place cells?
Cells that fire when on human/animal moves to a particular spot. The memory of and environment may be stored as a specific combination of place cell activities in the hippocampus.
71
What are grid cells?
Cells that fire when rats pass the points of a hexagonal grid. The brain might use this pattern as a coordinate system for spatial navigation. There is a connection to place cells as well.
72
Describe the amnesia of Alzheimer's Disease
- begins with slight loss of memory and progresses to dementia
- major anterograde and retrograde amnesia in explicit memory tests
- deficits in short term memory and some types of implicit memory (verbal and perceptual)
- implicit sensorimotor memory is intact (ex. pavlovian conditioning, playing piano)
73
What causes the amnesia seen in Alzheimer's Disease?
Basal forebrain degeneration
- decreased acetylcholine
- acetylcholinesterase inhibitors are a common therapeutic approach
Diffuse damage
74
How does amnesia after concussion provide evidence for consolidation?
Posttraumatic amnesia:
- retrograde amnesia for the period before the blow
- some anterograde amnesia after
- concussion + coma: severity of the amnesia correlated with the duration of the coma
- period of anterograde amnesia suggests a temporary failure of memory consolidation
- when you first learn something it is in a stage that is very easy to disrupt; if information is allowed to consolidate normally, it will strengthen and persist in long-term memory; if disrupted, information will be lost and not consolidated into long-term memory
Information needs to process for a period of time, and concussions can disrupt this process, causing failure to consolidate.
75
Memory consolidation
- information that is recently learned is in a very fragile state
- behavioural information can overwrite labile information (ex. finding out your friend is pregnant vs. a boring fact)
- once the window of fragility has passed, information becomes more resilient and is less likely to be disrupted
76
Synaptic consolidation (aka local consolidation)
- involves local changes at the synapse
- depends on protein synthesis; needed for information to persist
- minutes to hours
- blocked protein synthesis = blocked consolidation
77
System consolidation
- involves gradual (and usually slower) reorganization of the brain regions that support memory
- often measured as sensitivity of long term memory to hippocampal damage
- days-weeks-years, depending on type of memory
- evidence that memories are eventually unloaded form the hippocampus and stored in the neocortex
- hippocampus memory can become hippocampus independent
78
Reconsolidation
Traditional view: short-term memories consolidate over time, and once a memory is a long-term memory it remains fixed or permanent.
Reactivated memories are also in an active/labile state and stabilize over time into an inactive state. Remembering may return inactive memories to an active state.
Reconsolidation allows the updating of long-term memories.
79
Hebb's cell assembly concept:
1. the cell assembly
2. activation of the cell assembly by a stimulus
3. reverberating activity continues activation after the stimulus is removed (cells continue to fire for some time after)
4. Hebbian modification strengthens the reciprocal connections between neurons that are active at the same time
5. the strengthened connections of the cell assembly contain the engram for the stimulus
6. after learning, parietal activation of the assembly leads to full activation of the engram (leads to pattern completion)
7. "Circle"
An old model that fits our current understanding of synaptic consolidation.
80
Multiple Trace Theory
The hippocampus stores memories permanently, but they become "stronger" over time.
With each reactivation a new "index" in the hippocampus, a new trace is created. Multiple "indexes" are less likely to be damaged by lesions.
81
Standard Consolidation Theory
The hippocampus stores memories temporarily. The memory trace is transferred from the hippocampus to various cortical regions.
82
After formation, cells need to: _________, _________, and _________
1. Differentiate (ex. muscle cells, liver cells, neurons, glia...)
2. Migrate to the appropriate location
3. Establish functional relations with other cells
83
Early embryonic cells are _________
totipotent (all cells are the same when first formed)
84
Embryonic development of the central nervous system
1. Induction of the neural plate
2. Neural proliferation
3. Migration and aggregation
4. Axon growth and synapse formation
5. Neuron death and synapse rearrangement
85
Induction of the Neural Plate
- in the ectoderm
- ~3 weeks after conception: neural plate, neural groove, neural tube central canal and neural crest
- neural crest represents the cells that will become the adult peripheral nervous system
86
What happens to neural plate cells during induction?
They become multipotent, meaning they can develop into any type of nervous system cell.
87
What are the 2 properties of stem cells?
1. They have unlimited divisions without differentiation
| 2. They have the potential to differentiate into different cell types
88
After the _________ of the neural tube, there is a massive _________ in the number of cells. This is part of _________.
closure, increase, neural proliferation
Occurs mainly in the ventricular zone, and there are species-specific sequences.
89
Migration and Aggresgation
Many of these newly formed cells migrate away from where they are born, then they complete their differentiation once they reach their destination.
90
What are 2 forms of neuronal migration?
1. Glial Mediated Locomotion
- occurs in a radial manner
- medial cells provide temporary "scaffold" for neuronal migration
- partially differentiated neurons "crawl" along this network of glial cells
2. Somal Translocation
- radial, tangential, or multipolar
- extension explores environment for chemical signals ("guidance molecules")
91
Aggregation
Once migrated, the cells come together and acquire the organization typical of the CNS structure to which they belong (cortex, nuclei, hippocampus...)
Cell-adhesion molecules (CAMs), on the surface of neurons and glial cells; important in migration, recognition, and adhesion.
92
Give examples of neuron migration disorders:
Kallmann Syndrome: abnormal genitals and dysfunctional sense of smell related to failed migration of neurons secreting sex hormones and coding for odours.
Dyslexia and Schizophrenia: neural migration errors implicated...
Lissencephaly: "smooth brain", sever mental retardation
93
Axon Growth and Synapse Formation ("synaptogenesis")
Growth cone: at the tip of a growing axon; it extends and retracts filopodia (finger-like processes).
94
Chemoaffinity Hypothesis
Target-specific chemical labels, hypothesis supported by in vitro studies (no spatial cues, only chemical), and the discover of several such chemical labels.
95
Explain Sperry's classic study of eye rotation and regeneration
- When an insect is dangle in front of a normal frog, the frog strikes it accurately with its tongue
- When the eye is rotated 180° without cutting the optic nerve, the frog misdirects its strikes by 180°
- When the optic nerve is cut and the eye is rotate by 180°, at first the frog is blind, but once the optic nerve has regenerated the frog misdirects its strikes by 180°. This is because the axons of the optic nerve, although rotated, grow back to their original synaptic sites
96
Topographic Gradient Hypothesis
2 intersecting gradients (up-down and left-right) of chemicals on the originating tissue guide axonal growth from one topographical array (such as a retina) to another (the optic tectum).
Growth cones are capable of integrating information from different signals until they find their location that is specific to their specific cell.
97
Synapse Formation = Synaptogenesis
Synaptogenesis is neuron-neuron chemical "talk".
Another key role for glial cells (astrocytes):
1. In vitro studies: neurons cultured with astrocytes form 7 times as many synapses as those without astrocytes
2. In vivo studies: synapse-promoting and inhibiting signals interact...
98
Neuron Death and Synapse Rearrangement
There is an overproduction of neurons, about 50% more than are actually needed; the "surplus" neurons die. The more potential for connections means the more likely connections will be formed.
99
What are the functions of neuron death?
1. Neurons that make incorrect connections die. Developing neurons are very promiscuous and make lots of connections; not all are essential.
2. New neurons replace the "lost" neurons and make more focused synapses. Cell death increases the overall accuracy of synaptic connections.
100
What are the 2 general types of neuron death?
1. Apoptosis: active process of cell death. A "clean" process = active, programmed "cellular suicide"; attracts microglia to clean up and prevent inflammation.
2. Necrosis: passive cell death. A "dirty" process; can cause inflammation as cellular structures "leak" into extracellular fluid.
101
Cancer occurs when cell death is ________.
reduced
102
Neurodegenerative diseases occur when cell death is ________.
increased
103
What causes neurons to die?
Competition for target-supplied neurotrophins.
104
What are some functions of neurotrophins?
1. promote neuronal growth
2. promote neuronal survival/maintenance of synapses
3. can function as axon guidance molecules
4. can stimulate synaptogenesis
5. absence can actively trigger apoptosis
105
Postnatal development of the prefrontal cortex
Sensory and motor areas reach full maturity before cognitive areas.
Relatively slow, more gradual development into late adolescence. Linked to parallel development of "higher" cognitive functions... "Executive functions".
106
Give examples of executive functions
1. working memory
2. planning and carrying out sequences of actions
3. following rules for behaviour
4. context dependent inhibition of appropriate responses
107
Explain error perseveration
Making the correct response under certain rules, but then the rules change and person has to figure out the change. Never actually told what the rule is, they only receive feedback if what they are doing is right or wrong.
7-12 month old infants and patients with schizophrenia exhibit perseveration, which means a failure to inhibit original, learned response, which is now incorrect.
108
What are 2 types of experience?
Permissive experiences (necessary; ex. light in the eye).
Instructive experiences (influential; ex. early music training).
109
What are 2 effects of timing?
Critical period (absolutely essential; rare).
Sensitive period (greater effect of stimuli during a certain period).
110
What are 3 possible mechanisms of experience effects on neurodevelopment?
1. Direct Gene Replication (ex. for cell adhesion molecules involved in cel adhesion and migration).
2. Neurotrophin Release Regulation: post synaptic release affects pre-synaptic survival.
3. Regulation of Spontaneously Active Neural Circuits
111
What are some neurodevelopmental effects of rats being reared in an enriched environment?
- thicker cortices
- more synapses
- more dendritic spines
112
Animals reared in the dark have ________ problems and ________ synapses in visual cortex.
vision problems, fewer
113
What happens to neurodevelopment when both eyes are blindfolded?
Cortical degeneration
114
What happens to neurodevelopment when only one eye is blindfolded?
There is accelerated cortical degeneration. Thought to be because there is competition between left and right eyes for cortical input.
115
Why is Autism so complicated to study?
It is very heterogeneous, meaning it varies from person to person. There are usually common core functions, but there are many other non-diagnostic functions and are very variable.
116
What are the 3 symptoms for diagnosis of autism?
1. Reduced capability of interpreting others' emotions
2. Reduced social interaction and communication
3. Preoccupation with a single subject/activity
(these are apparent before the age of 3)
117
Autism
Functions can be impaired, normal, or improved.
Even when severely mentally retarded, patients normally preserve: rote memory - musical and artistic abilities, the ability to solve jigsaw puzzles.
118
What does savant mean, in terms of the ASD.
Intellectually affected individuals who display amazing and specific cognitive or artistic abilities.
119
What are some common physical features in autistic children?
Ears: square shape, low on head, rotated slightly backwards, tops flopped over
120
What is a known environmental factor that leads to autism?
Thalidomide: morning sickness medication that caused many, many birth defects. Used in the first few weeks of pregnancy, which means that neural development is taking place that early in pregnancy.
121
What are the 4 phases of brain growth in autism?
1. slight prenatal undergrowth
2. rapid and large overgrowth at 6-14 months
3. overall slow down in growth rate at age 1-5
4. gradual decline in brain size; by adolescence brain size is no different from that of average healthy brains
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