Human Cognitive Developmental Neuroscience Jan 27
Wiki Definition Developmental cognitive neuroscience is an interdisciplinary scientific field that is situated at the boundaries of Neuroscience Psychology Cognitive Development Psychiatry
What it is From birth to teen ears, there is a 4-fold increase in brain volume. There are also marked improvements in motor, cognitive, & perceptual abilities. Human developmental cognitive neuroscience considers the relationship between these events. Study of hierarchical change processes
Waddington (1957) Development is like a ball rolling down an uneven surface, able to take different directions as a function of its intertia, direction, and the landscape. Typical development would see balls ending up in the same general areas and atypical development would be balls in different areas of the landscape.
What it isn t (or shouldn t be) Brain mapping at different ages. Ex. Hippocampus lights up in task A in adults but not kids. Hence hippocampus develops between childhood and adulthood
Brain mapping at different ages. Ex. Hippocampus lights up in task A in adults but not kids. Hence hippocampus develops between childhood and adulthood Not shocking! What it isn t (or shouldn t be)
Brain mapping at different ages. Ex. Hippocampus lights up in task A in adults but not kids. Hence hippocampus develops between childhood and adulthood Not shocking! and So What? What it isn t (or shouldn t be)
Was this a genetically predetermined change in hippocampal activity? Did it result in some change in memory? Was the change in hippocampal function driven by some environmental exposure in this age-range? Would it have happened without the exposure? Questions Unanswered
Prolonged and delayed development of the human brain The human brain develops much slower than that of other primates or mammals. The more delayed the brain development is the larger will the relative volume of the later developing structures (neo-cortex) be.
Postnatal development: progressive processes By the 7 th month of gestation almost all neurons are present. What grows postnatally, are synapses, dendrites, and fiber bundles connecting brain areas. Also, the neurons get surrounded by myelin sheaths which allow for more efficient (saltatory) transmission of the electrical current.
Growth of the dendritic tree On the level of single neurons, the dendritic tree increases in size (longer axons) and complexity. Synaptic contacts between cells become denser. Peak synaptic density differs with region: Auditory cortex: 3 months Visual cortex: 4-12 months Prefrontal cortex (PFC): > 1 yr Johnson 2005: 28 At peak, levels of 140-150% of adult densities are measured.
Postnatal development: regressive processes Glucose level: after a sharp postnatal rise up to 150% of adult level, it decreases again to adult levels at about 9 yrs of age. Synaptic density: after a peak, synapses are pruned back to adult levels. Again, the timing of this pruning differs with region. The initial overproduction is important for brain plasticity. synaptic density glucose uptake The fact that the peak of glucose uptake does not coincide with the peak in synaptic density shows that reduction of synapses/neurons/ axons, etc. may not be the reason for lower brain metabolism.
Studying Brain Development Structural change: What do we know? Total volume increases White matter increases Grey matter increases and decreases Heterochronic change Giedd et al, Nature Neuroscience, 1999
So, brain stuff grows and new cognitive, emotional, motor, perceptual processes emerge as a result of the genetically predetermined growth, right? Probably not. Got it!
Cause of developmental change Deterministic epigenesis Unidirectional structure-function development: Genes brain structure brain function experience Certain cognitive functions are either present or absent at a point in time. Probabilistic epigenesis Bidirectional structurefunction development: genes brain structure brain function experience Development is a progressive restriction of possible states and paths development depends on constraints operative at a given time
Major theoretical approaches Maturation Interactive Specialization Skill Learning Neuroconstructivism
I. Maturation A Theory Born of Monkeys? One of Major Proponents -Adele Diamond The goal is to relate the anatomical maturation of specific regions of the brain to newly emerging sensory, motor, and cognitive functions. Ex.
AnotB and Delayed Response
After several A trials
Switch hiding to Well B
Error
Given this evidence from monkey work, it is inferred that DLPFC in infants who make this error, < 9 months, is not functional. Maturation makes accurate performance possible. AnotB as Marker Task for Prefrontal Function
II. Interactive Specialization Major Proponent Mark H. Johnson Acquiring a new skill in development does not entail the maturation of a new structure but rather the reorganization of interactions between existing, partially active structures. The onset of new behavioral competencies is associated with changes in activity over several regions, and not just with the onset of activity in on or more regions.
II. Interactive Specialization Changes in white matter connectivity underly changes in behavioral competencies Assumption that there is no direct structure-function relationship (DLPFC and inhibition in AnotB) but rather a network of regions
ERP experiments with simple word recognition tasks show that differences between known words and controls are found over large areas but the difference narrows to the leads over left temporal lobe (implicated) when vocabulary reaches 200 words irrespective of maturational age. Neville, Mills, Lawson (1992) Evidence Ex. 1
Patients with William s Syndrome have cortical activation patterns that are different from controls even in areas where they perform as well as controls. Idea is that initial brain abnormalities are compounded by deviant patterns of interaction and connectivity between regions. Evidence Ex. 2
III. Skill Learning Hypothesis Adult fmri data suggests changes in the neural basis of behavior that are a result of acquiring perceptual or motor expertise. The idea is that some of the changes in the neural basis of behavior in infancy will mirror those observed during more complex skill acquisition in adults
Ex. Face Processing In humans, face perception is uniquely associated with activity in the fusiform face area located in the fusiform gyrus in the inferior temporal lobe (e.g., Kanwisher). Face Module
Visual Expertise? Gauthier and colleagues suggest that faces are special because we have become experts at within-category discriminations Claims that becoming an expert at "Greeble" discrimination involves the fusiform face area, as do other types of within-category discrimination (e.g. model car collectors) Experiment: perhaps fusiform area can be trained to recognize novel objects. Greeble learning experiment. Over 10 hours on naming Greeble objects
Result FFA learns to respond to Greebles. Perhaps this is how development proceeds emergent modularity
Durston, M.C. Davidson, N. Tottenham, A. Galvan, J. Spicer, J.A. Fossella, & B.J. Casey, 2006
Neuroconstructivism Gene/gene interactions, gene/ environment interactions and the processes of ontogeny (pre and postnatal) are all considered to play a vital role in how the brain progressively sculpts itself and how it gradually becomes specialized over developmental time. Karmiloff-Smith, Marschal, Johnson
Functional brain systems are interrelated with other functional systems, and are located within the body and environment. All of these levels provide sources of information such that only fragments need to be represented by each to support adaptive behavior and change.
Cooperation-integration of multiple contributors to a function Competition -from the many initial contributors to an immature function, only a subset will be involved in the mature function. Chronotopy- stresses that time is a dimension of development. e.g., genes express at specific times, need to say words before you can build sentences. Outocome of these developmental processes are partial representations. Context-dependence
Ex. Neuroconstructivist approach Visual Perception The ventral stream of visual object processing (V1 to IT) Competition- occurs at each stage along stream and reflects both bottom-up and top-down biases Cooperation-in order to identify an object, it is necessary to group features of the visual input that belong to that object (color, orientation) and to segment them from the background. Involves feed-forward and feedback connections between areas involved in object perception Chronotopy-later developing neurons in higher-order areas can exploit the earlier, partial representations developed in lower, peripheral regions.
In Sum Ongoing research in the field is designed to address which of these (if any) approaches best captures brain/behavior interactions developmentally Discovery in this field has the most profound (arguably) influence on developmental disorders (autism, ADHD)
Functional specialization of regions of the cerebral cortex arises through intrinsic genetic and molecular mechanisms Alternatively, some aspects of human functional brain development involve a prolonged process of specialization that is shaped by postnatal experience. Two Developmental Neuroscience Global Perspectives: Nature/ Nurture
Human infant is born with innate modules ad core knowledge relevant to the physical and social world. Alternatively, many of the changes in behavior observed during infancy are the result of general mechanisms of learning and plasticity. Two Cognitive Development Global Perspectives: Nature/ Nurture