Transcript Chapter 15: Johnson, M. H. The human social brain: An *evo

Chapter 15: Johnson, M. H. The human social brain: An “evodevo” perspective (pp. 309-319).
The role of ontogeny in the evolution of the
human brain. Is the human brain genetically
designed to assume its final adult form?
Important quote from p. 311
“In contrast to the view the cortical
specialization for cognitive functions is “hardwired,” the empirical evidence indicates that
each human infant’s brain “discovers” the
typical pattern of cortical specialization
afresh.”
Evo-devo
• The evolutionary-developmental biological approach
“evo-devo” argues that the specific course human
brain development is itself an adaptation; evolution
designed the human brain specifically so it would
complete its development in an intensely social context
in order to be unique kind of information-processing
organ.
• Ultimately what natural selection “selects” is a
particular developmental trajectory leading to a certain
phenotypic state.
Origins of human cortical specialization
• Two theories
• Protomap theory: most important factors are intrinsic
(specified precisely by genes) and early occurring, not
dependent on neuronal activity.
• Protocortex theory: most important factors are extrinsic
(dependent on contextual inputs) and later-occurring, and
require neuronal activity.
Protomap
• Protomap support: Evidence from
mice studies that disrupting thalamic
inputs prenatally to cortex (via
knockout genetics) has only limited
affect on differentiation of newborn
cortex.
• Criticisms:
• Pre-natal neuronal activity could still
be important in differentiation of
newborn brain
• True differentiated “boundaries?” or
gradual changes in graded expression
• Thalamic inputs appear essential in
development of visual cortex in
primates
Interactive specialization
• Compromise position: intrinsic factors
(genetic “blueprint”) provides only for
graded zones of varying gene expression in
brain where functional specializations are
“poised” but not determined to arise.
Inputs and neuronal activity necessary for
functional specializations to ontogenetically
emerge within graded zones.
• Author’s model: Interactive specialization
• Functional specialization arising from
cortical interaction. As regions of the brain
interact with each other over the course of
development they “fine turn” each other’s
functions from general to increasingly more
specific.
Fusiform face area
• Ex: Fusiform face area
• Intrinsic constraints: Located on the temporal or ventral visual
stream pathway, receives inputs from pvc related to object
patterns. Also develops strong connections to hippocampal cortex
associated with memory storage. Storage and recognition of object
patterns. But necessarily faces?
• Subcortical biasing of eventual cortical specialization?
• Studies by author show that certain minimal face-like patterns
attract infant’s visual attention and that this appears to be driven by
subcortical brain activity.
Subcortical biasing of cortical specialization
• Evidence from imprinting studies with chicks
• Newborn chick imprint on moving objects see shortly after birth
• Imprinting appears to be controlled by intermediate and medial
part of mesopallium of chick brain (IMM; corresponds to
mammalian cortex)
• Lesioning IMM has greater detrimental effects on artificial
“imprints” (red balls, boxes, etc) than natural ones.
• Independent subcortical structure controls attention/orientation
biasing (probably optic tectum; superior colliculus in mammals)
• Two stage process: optic tectum biases chick to seek out and
attend to hen-like objects; IMM drives imprinting process. Similar
processes going on in human face processing?
• IMM and FFA are positioned similarly functionally in the brain
(receiving partially processed visual inputs; “tutored” socially after
birth).
Necessity of evo-devo approach
• Subcortical driving of cortical development
requires external, environmental inputs.
• By delaying brain development until it (brain)
is in the appropriate social context allows for
greater information extraction and retention
during the course of this process.
• This in turn along with increasing cortex size
creates increasing cortical processing power.