Download plastic

Origin of Mind
Chapter 4
Evolution and Development
of Brain and Cognition
pp.85-124
Is the Human Mind Unique?
It is unique in its advanced level of development, but not in the
process by which it achieved this development.
The human mind is a product of the activity of the brain, and
the human brain (like any other brain) is a product of
evolutionary selection pressures.
Selection pressures have produced not only the innate instincts
of simpler animals, but also the most highly advanced forms of
human cognition.
Continuum of Brain Plasticity
CONSTRAINED
more specific
governed by genes
inherited from ancestors
Better suited for
addressing invariant
features of the
environment
PLASTIC
more adaptable
governed by experience
developed over time
Better suited for
addressing variant
features of the
environment
Inheriting the Brain: The Tree of Life
Inheriting the Brain: Homologous Structures
A homologous characteristic is a trait that appears in two or
more organisms due to their sharing a common ancestor.
Inheriting the Brain: Homologous Structures
Humans share many homologous brain structures and attributes
with other mammals. This includes the appearance of the
neocortex, which is the newest and outermost layer of the
cerebral cortex.
- Thalamus
a. Superior colliculi
b. Inferior colliculi
- Hypothalamus
- Hippocampus
- Neocortical regions
a. Auditory
b. Visual
c. Somatosensory
Inheriting the Brain: Neocortical Regions
p.91
Inheriting the Brain: Genes
Humans also share certain homologous genes with other
mammals (and even non-mammal species) that control key
aspects of the prenatal
development of the brain.
However:
a. Humans have a greater
number of genes that are
devoted to brain development.
b. Some homologous genes may
be expressed differently in
different species.
Inheriting the Brain:
Two Models of Neocortical Development
Arealization – formation of the functional subdivisions of the
neocortex (e.g. visual cortex) during prenatal development.
1. Intrinsic Model: Arealization is a result of the characteristics
of the neocortex itself.
Protomap hypothesis: The neocortex differentiates automatically
during its development, according to genetic controls.
2. Extrinsic Model: Arealization is a result of thalamic inputs.
Protocortex hypothesis: The neocortex is undifferentiated until
the thalamus directs particular neural signals (e.g. auditory) to a
particular neocortical area, causing subdivisions to form.
Inheriting the Brain: Comparative Ecology
Comparative ecology – the study of variations in the ecological
niche of different species.
When we compare species that are closely related (having a
recent common ancestor) but have adopted different survival
strategies, we can observe alterations in brain organization that
are not likely the result of long-term evolutionary changes.
When a body part becomes more specialized for obtaining food,
the corresponding area of the somatosensory cortex (which
contains a sensory “map” of the body) can become enlarged.
This is called cortical magnification (see next slide).
Inheriting the Brain: Comparative Ecology
p.100
Molding the Brain:
How Experience Shapes The Mind
While it is certain that selection pressures allowed us to develop
brains in the first place, selection pressures are not necessarily
responsible for the specialization of all brain areas.
Most notably, if the neocortex were to expand for reasons other
than selection pressures, the resulting unspecialized neocortical
areas could make the brain highly plastic. If so, the plasticized
brain could be profoundly “molded” by incoming stimuli.
Molding the Brain: Allometric Expansion
Allometry - systematic relations among different features of the
body.
1. There is an allometric relation between body size and brain
size: they tend to roughly maintain their ratio. It is conceivable
that an increase in body size (perhaps due to climatic pressures)
caused an incidental allometric expansion of the brain. However,
the body-brain size relationship is unreliable.
2. Finlay and Darlington (1995) – based on an analysis of the
sizes of 12 brain regions in 131 species, they proposed that a
neocortical expansion due to genetic changes affecting
progenitor cell division had resulted in an incidental allometric
expansion of other brain areas.
Molding the Brain: Allometric Expansion
cont'd.
...However, other researchers have analyzed the same data set
as Finlay and Darlington (1995) and have drawn a different
conclusion: that ecological and social adaptations, not allometric
expansion, caused the increases in neocortical volume.
This conclusion was further
solidified by a comparison of
the brain proportions of New
and Old World monkeys.
These geographically
separated but socially similar
groups demonstrated
convergent evolution of their
brain proportions.
Molding the Brain: Injury and Learning
Brain injury, or the amputation of a body part, can result in
subsequent reorganization of disrupted cortical functioning.
Learning, particularly rehearsal (repetitive actions) can lead to
changes in cortical functioning. Similarly, stimulation with or
deprivation of certain stimuli can alter the behavior of the
cortex.
Functional adaptations due to injury and learning are examples
of plasticity.
Soft Modularity
Refer to TABLE 4.1 on p.114, and TABLE 4.2 on p.117 for a
complete explanation of the types of modules and plasticity.