Chapter 15 : Johnson, M. H. The human social brain: An “ evo-devo ” perspective (pp. 309-319).

1. Chapter 15: Johnson, M. H. The human social brain: An “evo-devo” 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 “hard-wired,” the empirical evidence indicates that each human infant’s brain “discovers” the typical pattern of cortical specialization afresh.”

2. 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.

3. 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.

4. 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

5. 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.

6. 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 subcorticalbrain activity.

7. 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).

8. Necessity of evo-devo approach • Subcorticaldriving 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.