Investigating the Developing Brain: New Techniques and Questions in Cognitive Neuroscience

1. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press Chapter 15 Development “Life is a flame that is always burning itself out, but it catches fire again every time a child is born.” George Bernard Shaw fMRI study of infant speech processing

2. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press Chapter Outline 1.0 Introduction 2.0 Prenatal development: from blastocyst to baby 3.0 The developing brain: a life-time of change 4.0 Developing mind and brain 5.0 Early brain damage and developmental plasticity 6.0 Summary

3. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 1.0 Introduction New techniques for investigating the developing brain The field of developmental cognitive neuroscience is a young one: the advent of new non-invasive ways to measure brain function in infants and children has literally revolutionized the study of human development. fMRI study of infant speech processing

4. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 1.0 Introduction New techniques for investigating the developing brain New techniques for processing brain images allow us to assess key aspects of brain growth during childhood -- such as gray-matter density and cortical thickness

5. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 1.0 Introduction The mystery of the developing brain: old questions and new A central question in human development is how the trading roles of nature and nurture contribute to brain growth. A related issue is to what extent the brain is flexible (or ‘plastic’) in adapting to new situations in its environment and to recover from damage. Neuroimaging techniques are allowing us to investigate these questions in new and exciting ways.

6. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Epigenesis Does our genetic makeup predetermine who we will become? Or does our experience shape who we are? Clearly both genes and the environment have an impact on the developing human. A central question: does gene expression unfold, followed by the development of brain structures and functions that later are affected by experience? Or does experience -- the local environment, whether within a cell, a system, or the brain itself -- have an affect on gene expression?

7. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Nature and nurture: Bidirectional influences on development One approach to understanding the trading roles of genetics and experience on development was put forth by Gottlieb and Halpern (2002) who proposed that there are bidirectional influences between genetic expression and the environment during epigenesis.

8. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby The anatomy of brain development Much of early brain development occurs in the first weeks following fertilization. Shortly after conception, a fertilized cell (zygote) undergoes a rapid process of cell division.

9. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby The anatomy of brain development This results in a cluster of proliferating cells call the blastula that resembles a bunch of grapes. In mammals, blastulation leads to the formation of a blastocyst. The blastocyst has an inner cell mass and an outer cell mass, and is comprised of 70-100 cells. The next stage of development will lead to formation of the embryo.

10. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby The anatomy of brain development After a few days, the blastocyst differentiates into a three-layered structure called the embryonic disk. Each of these layers will subsequently differentiate into a major organic system. The endoderm (inner layer) will become internal organs, the mesoderm (middle layer) will become skeletal and muscular structures, and the ectoderm (outer layer) will develop into the skin surface and the nervous system.

11. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby The anatomy of brain development Development of the nervous system begins with a process known as neurolation. A portion of the ectoderm (outer layer) begins to fold in on itself to form a hollow cylinder called the neural tube. The neural tube differentiates along three dimensions: length, circumference, and radius.

12. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby The anatomy of brain development The vertebrate brain and spinal cord develop from the neural tube. Lateral (top panel) and dorsal (bottom panel) views of human embryos at successive stages of embryonic development show the growth pattern of the forebrain, midbrain, and hindbrain.

13. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Proliferation zones The vast majority of the cells that will compose the brain are born in proliferation zones in the neural tube. These zones are close to the hollow center portion of the tube that will later become the ventricles of the brain.

14. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Neural migration After young brain cells -- neurons -- are born, they have to migrate from the proliferation zones to the particular region where they will be employed in the mature brain. Two types of neural migration: Passive cell displacement where young cells are simply pushed further away from the proliferation zone by more recently born cells.

15. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Neural migration Two types of neural migration: Passive cell displacement Inside-out pattern is a more active form of migration and involves the young cell moving past previously generated cells to create an ‘inside-out’ pattern. This pattern is found in the cerebral cortex and in some subcortical areas that have a laminar structure (divided into parallel layers).

16. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Neural migration The best studied example of active neural migration comes from the prenatal development of cerebral cortex and the radial unit model proposed by Pasko Rakic in 1988. According to this model, the laminar organization of the cortex is determined by the fact that each relevant proliferative unit gives rise to about 100 neurons. The progeny of each of these units all migrate up the same radial glial fiber, with the latest to be born traveling past their older relatives

17. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Nature and nurture revisited • The prenatal environment can have long-lasting effects, both good and bad, in brain development. The developing infant is susceptible to events occurring within this environment. One such event is the incursion of a teratogen, defined as any agent that causes damage during the prenatal period. • Examples of teratogens are: • Prescription and even non-prescription drugs • Caffeine • Illegal drugs such as cocaine and heroin • Tobacco and marijuana products • Alcohol

18. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Teratogens: long-term effects of smoking during pregnancy Longitudinal studies assessing the long-term effects of smoking cigarettes or marijuana during pregnancy have provided new evidence about their impact on the child’s cognitive development. Results of a Canadian study following children from birth through age 16: Exposure to cigarette smoke resulted in lower general intelligence along with problems with working memory.

19. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Teratogens: long-term effects of smoking during pregnancy Results of a Canadian study following children from birth through age 16: Exposure to marijuana smoke resulted in deficits in executive functions such as attention and working memory, along with problems in visual processes such as visual integration and analysis. Exposure to marijuana smoke results in reduced right hemisphere activity and increased left hemisphere activity in frontal lobe circuits for visuospatial working memory.

20. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 Prenatal Development: from Blastocyst to Baby Prenatal music and voice perception What do babies know before they are born? Is it important for a mother-to-be to talk to her unborn baby? Is there an impact on later cognitive function? There has been a massive commercial effort to provide parents-to-be with material that is claimed to help the baby’s cognitive growth. The verdict is still out on whether these prenatal experiences actually affect later cognitive development, however, and new studies investigating this aspect of prenatal development are needed to provide scientific evidence in their support.

21. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 The Developing Brain: A Lifetime of Change The rise and fall of postnatal brain development • The newborn brain -- there are many additive changes that occur after birth: • overall brain volume quadruples between birth and adulthood • an increase in the size and complexity of dendritic trees of most neurons, called dendritic arborisation • an increase in the density of synapses, or synaptogenesis • an increase in the fatty sheath that surrounds neuronal fibers -- called myelination -- that increases the efficiency of electrical transmissions

22. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 The Developing Brain: A Lifetime of Change The rise and fall of postnatal brain development The newborn brain -- there are many additive changes that occur after birth: Dendritic arborisation of cells in visual cortex shows the increase in dendritic length between birth to adulthood

23. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 The Developing Brain: A Lifetime of Change The rise and fall of postnatal brain development The newborn brain: there are also regressive changes that occur after birth: synaptic densities also undergo a loss of synapses, called pruning. The timing of these processes varies between cortical regions.

24. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 The Developing Brain: A Lifetime of Change Regional differences in brain development For example, synaptic density in the visual cortex begins to reach adult levels after about 2 years of age, however synaptic density of prefrontal cortex does not reach adult levels until the teenage years.

25. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 The Developing Brain: A Lifetime of Change Regional differences in brain development Gray-matter densitychanges during the lifespan: gray-matter density decreases rapidly in some regions (such as the frontal cortex during adolescence) and more steadily in others (such as the superior temporal sulcus) during the lifespan.

26. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The first year of life: an explosion of growth and development We have many objective measures of brain development -- such as gray-matter density and overall brain volume: a key question in developmental cognitive neuroscience is how do those brain changes relate to cognitive development? Three aspects of cognitive development have been the focus of many developmental studies: language acquisition, executive function development, and social cognition.

27. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The first year of life: an explosion of growth and development Developing the linguistic brain: infant language capabilities Language is not a unitary system, but is comprised of many aspects of linguistic knowledge. Three core aspects of linguistic knowledge are: phonology (sound-based), syntax (grammar-based), and semantics (meaning-based).

28. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The first year of life: an explosion of growth and development Developing the linguistic brain: infant language capabilities A classic finding in adults is that language functions are left-dominant. Does this develop over time, or is present at birth? While this question is still being elucidated, an fMRI study of 2-3 month infants showed greater activation in temporal language regions on the left side in response to speech.

29. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The first year of life: an explosion of growth and development Developing the executive brain: What do babies know? Babies as young as 4 months old can make predictions about their physical environment: in this experiment, the baby is unsurprised at the possible event of a flap being raised and stopping at a solid block, but is surprised at the impossible event of the flap rotating through the solid block, indicating that he appreciates that objects are solid.

30. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The first year of life: an explosion of growth and development Developing the social brain: faces and places Face perception in newborns: newborn infants track schematic faces longer than scrambled faces or blank head shapes, indicating a preference for faces at birth.

31. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The linguistic brain: language acquisition While the first year of life represents an unparalleled stage of of explosive brain growth and cognitive development, many aspects of cognitive growth take years to mature -- such as language systems. Studies using EEG and event related potentials reveal a staged pattern of acquiring the sound-, meaning-, and grammar-based knowledge necessary for language acquisition.

32. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The linguistic brain: syntactic knowledge at age 2 years By the age of 2, children’s brains respond to syntactically incorrect sentences indicating that implicit processes for extracting grammatical rules are in place.

33. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The executive brain: taking cognitive control Even young infants must learn what information in their world is important and what is unimportant or irrelevant. These learning mechanisms fall under the general category of ‘cognitive control’ and have been the focus of much study in child development.

34. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The executive brain: taking cognitive control In adults, the prefrontal cortex is active for cognitive control tasks. Studies with children show that younger children exhibit broader, more diffuse brain activation in these tasks than adults. Brain figures (right) show regions of increasing and decreasing activation as a function of age (Casey et al., 2005).

35. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The executive brain: Attentional processes in childhood • An attention model proposed by Posner and colleagues has been combined with the Attention Network Task (ANT) to investigate attentional processes in adults. • Posner’s attention model describes three differing but highly overlapping neural networks for: • Alerting to new and relevant information • Orienting and reorienting to relevant information or stimuli • Executive control of attentional processes

36. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The executive brain: Attentional processes in childhood Konrad and colleagues (2005) used fMRI and a modified form of the Attention Network Task to investigate attentional processes in children aged 8-12 years. The task involves four different cue and target conditions to investigate alerting, orienting, and executive control of attentional processes.

37. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The executive brain: Attentional processes in childhood In the alerting condition, adults showed increased activation of the right cingulate gyrus (top) and in the brainstem (bottom) as compared to the children. Konrad and colleagues suggested that these results reflect differing ‘top-down’ modulation of alerting mechanisms in adults that may not be fully established in children in the age range 8-12 years.

38. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The executive brain: Attentional processes in childhood In the orienting condition, adults showed increased activation of the right temporal-parietal junction (top) as compared to the children. Children showed increased activation in the putamen and insula (middle) and in the superior frontal gyrus (lower) as compared to adults . These findings may represent the recruitment of differing brain regions for performing the tasks due to immature cognitive control mechanisms in children.

39. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The executive brain: Attentional processes in childhood In the executive control condition, adults showed increased activation in superior parietal cortex (left) and inferior frontal gyrus (right) as compared to the children.

40. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The executive brain: Attentional processes in childhood In the executive control condition, children showed increased activation in superior temporal gyrus (left) and superior frontal gyrus (right) versus adults . Cumulatively, this study shows a strikingly different pattern of activation for children as compared to adults in each of the attentional processes studied. More evidence is needed, however it may be the case that that cognitive control systems are functional -- but immature -- in young children as compared to adults.

41. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The social brain: face perception in childhood • Face perception has been the focus of many neuroimaging and behavioral studies in newborns, infant, children, and adults. Why is this area of research so important? • Investigating brain regions that may be specialized for perception of species-specific faces may shed light on the nature vs. nurture debate: • Are we predisposed to attend to, focus on, and interpret cues in faces? Or does our vast experience with faces provide information processing abilities that are not specific to faces but instead use general visual object perception networks?

42. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Developing Mind and Brain The social brain: face perception in childhood While infants clearly show a preference for looking at faces, the neural processes that underlie the decoding of emotional cues in faces are not well understood. Results of studies to date provide evidence that younger children have more diffuse brain responses to emotional cues, older children have more focal responses -- although not adult-like. Cumulatively, these findings indicate that face perception is a slow-to-mature process. While the nature vs. nurture debate rages on, it appears that both a predisposition to attend to faces and maturational processes based on experience are involved in human face perception.

43. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 5.0 Early Brain Damage and Developmental Plasticity Large and small scale perinatal brain damage What is the long-term outcome of early (perinatal) brain damage? In adults, brain damage due to stroke or injury typically leads to deficits that may be severe and long-lasting. Is this the case when damage occurs near birth?

44. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 5.0 Early Brain Damage and Developmental Plasticity • Three patterns of perinatal injury: • A large unilateral lesion involving most of one cerebral hemisphere (left) • A small lesion confined to one cerebral lobe (middle) • A deep lesion involving both cortical and subcortical regions (right)

45. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 5.0 Early Brain Damage and Developmental Plasticity Global versus local: visuospatial deficits One way to investigate the effects of early brain damage is to utilize tasks that have been shown to elucidate hemisphere-specific deficits in brain damaged adults: a copying task where the figure has both global and local (detailed) information. A classic finding is that right-damaged patients fail to copy the global aspects of the figure while left-damaged patients fail to copy the local aspects.

46. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 5.0 Early Brain Damage and Developmental Plasticity Global versus local processing in the brain An fMRI study of typical adolescents shows classic hemisphere asymmetries in processing global and local information; adolescents with unilateral brain damage show both global and local processing are accomplished in the undamaged hemisphere (Stiles et al., 2005).

47. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 5.0 Early Brain Damage and Developmental Plasticity What is the long-term outcome of early (perinatal) brain damage? The longitudinal studies of Stile and colleagues provide evidence that there may be long-lasting damage to cognitive processes, such as spatial cognition mechanisms used in decoding global and local information. However, they also provide evidence for a brain system that is highly flexible, with compensatory recruitment of neural territory in the undamaged hemisphere to support these types of mechanisms.

48. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 6.0 Summary The advent of new techniquesfor non-invasively studying human development has provided the means to address new questions about cognitive development, some of which were never addressable before -- such as what does a baby know before birth? Does an infant understand the grammar of language? The nature vs. nurture debate continues … At every stage of development, there are important genetic effects and biological constraints at work in the unfolding of the human brain and mind. Similarly, at each stage there are critical effects of the surrounding environment, whether at the level of a cell, a system, or the brain itself.