Circuits and Circumstances.
Nature v. Nurture.
15th January, 2015.
© R. Balbernie.
The Importance of Early Relationships:
A View from Interpersonal Neurobiology.
“Human relationships, and the effect of
relationships on relationships, are the building
blocks of healthy development. From the moment
of our conception to the finality of death, intimate
and caring relationships are the fundamental
mediators of successful human adaptation.” (p. 27)
National Research Council and Institute of Medicine
(2000) From Neurons to Neighbourhoods: The Science
of Early Childhood Development.
Committee on Integrating the Science of Early Childhood
Jack P. Shonkoff and Deborah A. Phillips, eds.
Washington D. C. :National Academy Press.
The brain is the only ‘computer’ that can:
adapt to any input by
changing both its own
software and hardware;
dictate the interests and
skills of the operator;
So eat your heart
and, crucially, it
never exists on its own.
This is simply how humans have evolved.
There may be exceptions.
Evolution and brain development.
Human babies are helpless and less
developed compared with most
mammals. – The primate with the
least developed brain at birth.
The pelvis changed to aid walking
as our ancestors became more
gracile, forcing the bones
surrounding birth canal to be
closer. But the enlarged skull
made birth risky. Homo sapiens.
Evolution of bipedal locomotion
lead to wider pelvic girdle in
females. This allowed bigger
babies with bigger brains.
Expanded brain size enabled tool
use and social complexity. Big
brains then selected for. More
processing power. Homo habilis.
Smaller babies needed!
Attachment, common to all
Early caregiving now alters
mammals, is co-opted by
the baby’s brain, allowing this
We never look back.
closeness to import culture.
“The evolution of human beings has consisted
largely of adaptation to one another.” (p. 27)
(Wright, R. (1996) The Moral Animal London: Abacus.
• “Our brains coevolved with culture and are
specifically adapted for living in culture – that is,
for assimilating the algorithms
and knowledge networks of
• “The human brain is the only
brain in the biosphere whose
potential cannot be realised
on its own. It needs to become part of a network
before its design features can be expressed.” (p.324)
Merlin Donald, (2001) A Mind So Rare. W.W. Norton & Co.
Culture is the mechanism for the survival of ideas.
Humans have evolved the capacity to use language in
order to teach and learn cultural information (e.g.
tool use, child rearing customs).
The evolutionary significance of ‘plasticity’.
As brains evolved and became more complicated
their formation became more patterned by the
surroundings in which they must function – the
‘knowledge networks of culture’– so that
specialised circuits are formed in response to the
demands of the local environment. The structural
organisation of the brain reflects it’s history.
“Most of human knowledge cannot be anticipated
in a species-typical genome …
and thus brain development
depends on genetically
based avenues for incorporating
experiences into the developing brain.” (p.53) Neurons to
Your brain is what you do with it.
It functions as an
using past experiences to
create a neurological
Thus preparing us for the next.
Flexibility enhances survival.
“Rather than slowly adapting specialised structures
in the brain to environmental demands over the
course of evolutionary time, selection has designed
a brain whose adaptation is its ability to adapt to
local environmental demands
throughout the lifetime of an
individual, and sometimes
within a period of days, by
forming specialised structures
to deal with these demands.”
(p 142) Buller, D. J. (2005) Adapting Minds.
The MIT Press.
So what do we adapt to?
“For the developing infant the mother
essentially is the environment.” (p. 78)
(Schore, A. N. (1994) Affect Regulation and the Development of the Self:
The Neurobiology of Emotional Development. New Jersey: Erlbaum.)
And how do we adapt?
“By initially overproducing connections that
have been spread to a variety of targets, and then
selecting from among these on the basis of their
different functional characteristics, highly
predictable and functionally adaptive patterns of
connectivity can be generated with minimal
prespecification of the details.”
(p. 202) Deacon, T. (1997) The Symbolic Species.
There is plenty of choice – A piece of brain
tissue the size of a grain of sand contains
100,000 neurons, and has 100,000,000
connections, all communicating with each other.
“Every physical feature of the human nervous system
– the brain cells, or neurons, that transmit information;
their axons and dendrites that reach great distances to
connect with one another; the tiny synapses that are
the actual sites of connection; and the supporting cells,
or glia, that keep it all going metabolically – responds
to life experiences and is continually remodeled to
adapt to them. The brain changes when you learn to
walk and talk; the brain changes when you store a new
memory; the brain changes when you figure out if
you’re a boy or girl; the brain changes when you fall
in love or plunge into depression; the brain changes
when you become a parent.” (p.6)
Lise Eliot. (2012) Pink Brain Blue Brain. London: Penguin.
Nurture and nature are inextricable.
“Genetic susceptibilities are activated and displayed
in the context of environmental influences. Brain
development is exquisitely attuned to environmental
inputs that, in turn, shape its emerging architecture.
The environment provided by the child’s first
caregivers has profound effects on virtually every
facet of early development,
ranging from the health and
integrity of the baby at birth
to the child’s readiness to
start school at age 5.”
Neurons to Neighborhoods.
Genes are not destiny.
• The epigenome is the operating system that controls
the structural genome by switching genes on and off.
• These chemical signals are written on top of the
gene without altering the genetic code.
• Such changes can be temporary or
enduring, the latter playing key roles in
brain and behavioural development.
• Early experiences cause epigenetic adaptations in
the brain that influence whether, when and how
genes build the capacity for future skills to develop;
e.g. how well or poorly we respond to stress.
“Structural genes … are codes for resources needed
for development. They are not the codes for the
course and end-points of development itself.” (p.30)
Richardson, K. (2008) How dynamic systems have changed our minds. pp. 25-40 in: Fogel,
King & Shanker (Eds.) Human Development in the Twenty-First Century. Cambridge:
Cambridge University Press.
Within the developing mind neural signaling sets
off the production of gene regulatory proteins,
which then attract or repel the enzymes that in turn
add or remove epigenetic markers. “For the growing
brain of a young child, the social world supplies the
most important experiences influencing the
expression and regulation of genes” (p.32). Siegel, D. J. (2012)
The Developing Mind (Second Edition). New York: The Guilford Press.
The new science of Epigenetics.
There is now a “growing body of work from the
developmental neuroscience field that supports the
view that epigenetic changes underlie the long-term
impacts of early-life experiences.” (p.404) Roth, T. L. & Sweatt, J.D.
(2011) Annual Research review: Epigenetic mechanisms and environmental shaping of the
brain during sensitive periods of development. The Journal of Child Psychology and
Psychiatry, 52 (4), 398-408.
Epigenetics refers to the
mechanisms that alter a gene’s
form, structure and function
without changing its sequence.
(Only the sequence is inherited.) It is as if certain
characteristics and behaviours are authorized while
others are prohibited, or switched off.
Early experiences alter gene expression.
(1) Early experiences spark
signals between neurons.
(3) Gene regulatory proteins attract or repel
enzymes that add or remove epigenetic markers.
Gene – a specific
segment of a DNA
(2) Neural signals
launch production of
proteins inside cell.
whether or not the
gene is ‘readable’
by the cell.
(4) Epigenetic ‘markers’ control where and how much
protein is made by a gene, effectively turning a gene on
or off, thus shaping how brains and bodies develop.
• Epigenetic changes allow a response to the
environment through changes in gene expression.
For the baby this environment is largely defined by
close relationships and family setting.
• Epigenetic modifications are inherited during
mitosis (and sometimes in meiosis) and can be
transmitted to the next
• Such intergenerational
persist into the fourth
generation despite a lack
of continual exposure to the original environment.
• Thus, in a negative
environment, mental health
difficulties might be transmitted
from parent to child (or even
from a grandparent) via a
• The emotional environment,
especially during pregnancy and
infancy, activates and silences
good and bad genes that are
crucial for mental well-being
and social and emotional
In the same way, more positively, the relationship
with the mother actively builds the baby’s brain.
The heightened states of excitation and elation that
the baby feels during interactions with the mother
correlate with biological changes involving
neurochemicals centrally involved in the regulation
of brain metabolic energy level and the maturation of
the cortex and limbic systems. This also triggers the
birth of new neurons,
protein synthesis and
neural growth. Thus
caregiving activates the
growth of the brain through
emotional availability and
The brain is comprised of four areas.
Growth of the brain occurs
from the inside out and the
You are born with 100 billion
brain cells, neurons, but these
are largely unconnected.
There can be about 10,000
synaptic connections for each
They can wire up at the rate
of 1 million per second!
You have more than 2 million
miles of neuronal fibres!
Growth from the bottom up and inside out.
Abstract thought, metacognition.
Strategic thinking, planning,
interpretation, setting priorities,
suppressing impulses, weighing
consequences of actions.
Formation & recall of memory.
insult may have a
Awareness Monitor stimuli for threat.
Fight, flight or freeze responses.
on the growth of
brain areas that
will receive input
from the affected
Procedural motor patterns.
Arousal / aggression.
(All autonomic functions)
Sleep cycles. Instincts.
Co-ordination of movement.
As the maturing brain becomes more specialized in
order to assume more complex functions, it is then
less capable of reorganizing and adapting.
But this does not imply it is impossible. See: Schwartz, J. M. & Begley, S.
(2002) The Mind and the Brain. New York: Harper Collins.
Many intrauterine and
perinatal insults can
alter migration of
neurons and have a
profound impact on
e.g. infection, lack of
smoking and alcohol.
Principal internal structure of a Multipolar Neuron.
Neurons have 3 sequential levels of information exchange, or messenger systems:
1) The communication across the synapse, that - 2) changes the internal
biochemistry of the cell, which - 3) activates mRNA (messenger ribonucleic acid)
& protein synthesis to change brain structure.
View of a synapse.
It is the process of
that stimulates each
neuron to survive,
grow and be sculpted
Experience-expectant brain growth.
• This take place when the brain is primed to receive
particular classes of information from the
environment in order to build basic skills.
• Since the brain over-produces synapses they are
‘forced’ to compete. This over-abundance of
synapses occurs during sensitive periods
• Neurons that fire together wire together.
• The ‘fittest’, or most used and
useful, synapses are selected;
and in neural development this
is defined by the level of
Initial growth of synapses.
And then it is all downhill!
6 year old.
14 year old.
Highly active synapses –
receiving more electrical
impulses and releasing a greater
amount of neurotransmitters –
stimulate their post-synaptic
targets more efficiently.
This heightened electrical
activity also triggers
molecular changes that
stabilise the synapse.
The axons of stabilised neurons become coated in
myelin, an electrical insulator. It plays a role in the
transfer of energy to neurons and may also support
This myelin sheath is
essential for the proper
functioning of the
This shows by an increase in white matter and a decrease in grey matter.
Less active synapses fail to stabilise, and so
eventually regress. It is a matter of: “Use it or lose
it!” right from the start. Synaptic pruning fine-tunes
the functional networks of the brain.
For the first 8 months after
birth the rate of creating
new synapses far outstrips
that of pruning. By age 1,
and through early childhood,
the rate of reabsorbing redundant connections gains
on the rate of creating new synapses. By
adolescence, in most cortical areas, this process
again reaches equilibrium.
Fewer but faster connections.
A second wave of synaptic proliferation and pruning
within the cerebral cortex occurs in late childhood;
and the final, critical part of this, affecting the
higher mental functions, occurs in the late teens.
This overproduction, or exuberance, occurs in the
parietal lobes – maintaining sense of self, logic and
spatial reasoning, connects senses with motor
abilities and creates the
experience of a sense of
our body in space; and the
temporal regions – linked
to auditory processing,
language and memory.
The maturation of grey matter in the cortex.
The regions that mature last – not until early adulthood –
are associated with higher-order functions such as
planning, reasoning and impulse control.
A decrease in grey matter shows
grey matter reflect selection of
neurons, organisation of neural networks and
enhanced processing efficiency. This occurs in a wave
that starts at the back of the brain and progresses to the front.
The prefrontal cortex (the area of ‘sober second
thought’, or the ‘chief executive’) is the last part
of the brain to mature. Adults depend on this area
of the brain to process emotional information,
resist impulses and exert voluntary control.
Unexpected stress may exhaust the prefrontal
cortex resources of the adolescent, undermining
executive functioning. Teenagers still rely heavily
on the amygdala to process
emotions, and frequently
read the cues wrongly so
the emotion, in self or other,
gets wrongly labelled.