Neural Plasticity of
Development and Learning
Galvan, 2010
Presented by Kristen Morin and Sunil Patel
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Neural Plasticity of Development and
Learning
I. Defining Development and Learning
II. Neural Plasticity
III. Progressive and Regressive Changes with Learning
IV. Plasticity of Developmental Timing
V. Neural Mechanism- Same or Different?
VI. Methodological Considerations/Potential Confounds
VII. Conclusions
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I. Defining Development and Learning
What is Development?
organismic changes as a result of growth, maturation, and/or
experience
What is Learning?
acquisition of a skill or knowledge through study, instruction,
and/or experience
The Common Denominator?
Experience
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The Debate: Are they...
Inseparable constructs [Casey et al., 2006]
•
Learning occurs within a developmental framework
Distinguishable by time periods [Smith and Thelan, 2003]
•
Learning: days, hours, months of practice,
•
Development: weeks, months, years of change
On a continuum [Galvan, 2010]
•
Both are processes that induce neural plasticity via shifts in mechanisms
•
e.g. Discrimination of phonetic speech sounds in all languages by infants [Kuhl et. al., 1997]
Complementary processes [Karmiloff-Smith, 1994] [Greenough et. al. 1987]
•
Biological predispositions (experience-expectant development) are subsequently modified by
experience (experience-dependent learning)
•
Evolutionary tendency to modify existing systems (avoids redundancy)
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... as a Continuum
Endpoints receive
inputs from both
processes
Experience-expectant
largely influence emergent phenotype (development)
utilize environmental information common to all members of a
species (common input) throughout evolutionary history (common
timeline)
neural changes follow phylogenic norm (typical plasticity)
Experience-dependent
greater influence in learning
utilize information from the unique experiences (specific inputs) of
each particular individual (fluid timeline)
neural changes result from individual experience [unique plasticity)
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Neural Plasticity of Development and
Learning
I. Defining Development and Learning
II. Neural Plasticity
III. Progressive and Regressive Changes with Learning
IV. Plasticity of Developmental Timing
V. Neural Mechanism- Same or Different?
VI. Methodological Considerations/Potential Confounds
VII. Conclusions
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II. Neural Plasticity
Functions in Development:
- acquisition of new information
Thinking and Learning
neurogenesis
activity dependent
synaptic plasticity
programmed
cell death
- adaptations to fluctuating
environments or conditions
- recuperation from injury
Changes in Neural
Organization
(Functional + Structural)
[Johnston, 2009]
neuronal circuitry
dendritic spines
Changes in Behavior
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Tools in Neuroimaging
Cross-Sectional Approach
e.g. Cortical representation of fingers in
musicians vs. non-musicians [Elbert et al., 1995]
[Pros] time and cost vs. [Cons] Lower
statistical power, potential confounding
variables, cohort effects
Longitudinal Method
e.g. Increased number of dendrites in visual
cortex of trained vs. untrained animals
[Greenough et al., 1979]
[Pros] high statistical power (within subject
comparisons) vs. [Cons] practice effects,
increased time and costs, lower retention of
subjects
Trans-cranial Magnetic
Stimulation (TMS)
e.g. Repeated TMS delivered to superior
temporal cortex causes macroscopic
changes in gray matter [May et al., 2007]
[Pros] Non-invasive, therapeutic potential
vs. [Cons] Subcortical effects difficult to
determine, measure, or ensure, potential
for inaccuracy when targeting specific ROI
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Neural Plasticity of Development and
Learning
I. Defining Development and Learning
II. Neural Plasticity
III. Progressive and Regressive Changes with Learning
IV. Plasticity of Developmental Timing
V. Neural Mechanism- Same or Different?
VI. Methodological Considerations/Potential Confounds
VII. Conclusions
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III. Progressive and Regressive
Changes with Learning
functional changes in neural activity following training are contradictory
Potential explanations for...
A. Regressive changes
Dual-processing framework of learning- central resources essential for
controlled processing in novices becomes less critical as skill level
improves to point of automatic processing [Chein & Schneider, 2005]
Developmental process of selective pruning
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III. Progressive and Regressive
Changes with Learning
functional changes in neural activity following training are contradictory
Potential explanations for...
B. Progressive changes
Constructivist Manifesto- connectivity progresses from fewer to greater
connections [Quartz & Sejnowski, 1997]
Recruitment of additional cortical units with practice
e.g. increased prefrontal and parietal activation related to working memory
capacity in children [Klingberg et. al., 2002]
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Neural Plasticity of Development and
Learning
I. Defining Development and Learning
II. Neural Plasticity
III. Progressive and Regressive Changes with Learning
IV. Plasticity of Developmental Timing
V. Neural Mechanism- Same or Different?
VI. Methodological Considerations/Potential Confounds
VII. Conclusion
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IV. The Plasticity of Developmental
Timing
Sensitivity to experience-expectant outcomes can be manipulated
-
Suggested in animal research (e.g. monocular deprivation effects in kittens reared in the
dark for 6, 8, 10 months) [Cynader and Mitchell 1980]
Processes reliant on experience-expectant mechanisms show
experience-related plasticity in developmental onset
-
Enrichment-experiments conducted with infants (e.g. infants show increased reaching
behavior with sticky mittens (and later without mittens) prior to typical motor development
allowing for actual grasping of objects) [Needham et. al., 2002]
-
Help avoid potential confounds of domain general experience with which older children
are already equipped.
Q: Does accelerating developmental timing result in neural
changes? And would these changes have downstream effects?
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Neural Plasticity of Development and
Learning
I. Defining Development and Learning
II. Neural Plasticity
III. Progressive and Regressive Changes with Learning
IV. Plasticity of Developmental Timing
V. Neural Mechanism- Same or Different?
VI. Methodological Considerations/Potential Confounds
VII. Conclusion
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V. Neural Mechanism- Same or
Different?
Same Learning Process: Prediction Error Signal (PES)
Neural activation in adults, accompanies learning by trial and error [Hollerman &
Schultz, 1998]
Thought to be mediated primarily through dopamine as a “learning signal”
event unexpected: increase firing rate/increase activation of dopamine rich-regions
event expected: decrease in dopamine signal [Fiorillo et al., 2003; 2008]
Different emergent plasticity across development
Infants: provides basic architecture for the neural system.
Adults: modifies existing system
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Utility of “Noise”:
Performance confounds between children and adults
Alternative neural strategies engaged by children to compensate
for system maturity of adults: confound or useful?
Dynamic Systems Theory utilizes variability in performance [Smith & Thelan, 2003]
-
developmental trajectories of change over short time periods (inter-subject
longitudinal) and/or over longer developmental span (cross-sectional)
Developmental vs. performance-related neural activity post-hoc
-
performance-matched subgroups, age subgroups, or neither [Schlagger et al., 2002]
[Brown et al.,2005]
-
Identified progressive and regressive changes associated with
age
-
potential to investigate training-related, age-related or
independent neural changes in future experiments
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Longitudinal training studies across
development
“The only way to identify the root of neural
plasticity as either experiential or
developmental is to conduct a longitudinal
study”
Recent studies have proven feaseability despite inherent challenges
-
[Durston et al., 2006] combined cross-sectional and longitudinal study of response inhibition
task
[Hyde et al., 2009] Implemented a training component building upon existing studies in adult
musicians and matched non musicians that showed structural and functional differences in
brain areas associated with music production.
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Longitudinal training studies across
development
Recent studies have proven feasibility despite inherent challenges
-
[Durston et al., 2006]
Longitudinal results: Attenuation of dorsolateral prefrontal cortex with age
Cross-sectional results: increased activation in ventral prefrontal cortex with
improved task performance
[Hyde et al., 2009]
Trained children showed greater behavioral improvements on music discrimination
and related tasks.
-
-
-
Structural changes in right perecentral gyrus, corpus collosum, and the primary
auditory region.
Findings consistent with same findings in adults, provide new evidence for traininginduced structural brain pasticity in early childhood.
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Questions to be Addressed
-
Which neural systems show greater or less training-related
plasticity earlier in development?
-
Greater plasticity in learning and receiving language input during infancy.
-
How do the timescales of neural plasticity change across
development?
-
Which behaviors cannot be “sped up” by exposure earlier in
development because of time locked experience-expectant
mechanisms?
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Neural Plasticity of Development and
Learning
I. Defining Development and Learning
II. Neural Plasticity
III. Progressive and Regressive Changes with Learning
IV. Plasticity of Developmental Timing
V. Neural Mechanism- Same or Different?
VI. Methodological Considerations/Potential Confounds
VII. Conclusion
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VI. Methodological Considerations
and Potential Confounds
Resources: Steep scanner costs and the need for a healthy sample size of
both children and adults, along with the need for specialized training staff call for
a very expensive experiment.
Subject attrition: Subject burden for training is high. Participants are
required to maintain cognitive and training engagement as they visit the lab for
multiple sessions. Paying closer attention and being sensitive to families’
needs can help achieve successful subject retention.
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VI. Methodological Considerations
and Potential Confounds
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Scanner Related Anxiety: Subjects, particularly
children, may have increased head movements as
well as increased vigilance which may skew
results.
•
Performance Differences: Without addressing
performance differences the differences in brain
activity between children and adults can
inappropriately be misinterpreted as maturational
differences.
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Neural Plasticity of Development and
Learning
I. Defining Development and Learning
II. Neural Plasticity
III. Progressive and Regressive Changes with Learning
IV. Plasticity of Developmental Timing
V. Neural Mechanism- Same or Different?
VI. Methodological Considerations/Potential Confounds
VII. Conclusion
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VII. Conclusions
- Consider if and how development differs from learning.
- How does this distinction translates to differences or
similarities in neural mechanisms?
- The local neural environment in which plasticity occurs is a
critical component of change.
- Inherent challenges in developmental study have prevented
significant advances in addressing plasticity-related
questions.
- It’s IMPORTANT to embrace longitudinal studies in
order to uncover mechanisms underlying plasticity
across development.
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