A Young Mind in a Growing Brain

Jerome Kagan, Norbert Herschkowitz

• Publisher: Psychology Press
• Year: 2006
• eBook ISBN: 9781135604950
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

A Young Mind in a Growing Brain summarizes some initial conclusions that follow simultaneous examination of the psychological milestones of human development during its first decade and what has been learned about brain growth. This volume proposes that development is the process of experience working on a brain that is undergoing significant biological maturation. Experience counts, but only when the brain has developed to the point of being able to process, encode, and interact with these new environmental experiences.

This book's aim is to acquaint developmental biologists and neuroscientists with what has been learned about human psychological development and to acquaint developmental psychologists with the biological evidence. The hope is that each group will gain a richer appreciation of both knowledge corpora. The authors hope to appeal to neuroscientists, psychologists, psychiatrists, pediatricians, and their students.

The idea for this book was born in 1993 when the authors--a leading developmental psychologist and a pediatrician--met for the first time and recognized the complementarity of their backgrounds and the utility of a collaboration. The reception of their first two papers motivated this attempt to synthesize the available information over a longer developmental era. Learning a great deal over the past decade, the authors hope that their enthusiasm provokes an equally intense curiosity in readers.

1
Brain and Behavioral Development

How Close a Relation?

The assumption that psychological phenomena originate in brain activity was not obvious to the wisest ancients. It took over two millennia to arrive at the hypothesis that the timing of the milestones that define human psychological development was partially dependent on the maturation of neuronal circuits. These insights required the invention of machines and methods that permitted scientists to observe phenomena that were completely hidden a hundred years ago.

The chemistry of the synapse, myelination, and profiles of neural activation accompanying psychological activity has led to reasonable speculations regarding the contribution of neurophysiology to psychological events and deepened our understanding of thought, feeling, and behavior, because two sources of evidence are always better than one. The discovery of bacteria permitted better explanations of disease, the discovery of microwave radiation enriched conceptualizations of the origins of the universe, and research on brain development enhances our comprehension of developing psychological phenomena.

Correlations between the profile of neural activity at a particular time—which we call a brain state—and a mental or behavioral product are most obvious in infancy and early childhood because the young brain’s structural immaturity limits the psychological properties that can be actualized. Hence, there should be a closer tie between the developmental stage of the nervous system and the age when the first psychological competences of our species appears. Two hundred years ago, almost 70% of American children lived in two-parent farm families, saw both parents regularly, and, of course, did not enjoy radio, television, or airplane travel. Today, almost 70% of American children live with one parent, or in families in which both parents work in separate places in nonagricultural jobs, and the child has access to radio, television, and occasional travel. Nonetheless, the ages when language, inhibition of prohibited acts, and the assumption of responsibility first appear have changed very little over the past two centuries (Rogoff, 1996). The evidence to be summarized affirms the brain’s modulation of psychological growth, although a detailed knowledge of the mechanisms that mediate the modulation remain mysterious.

There was so little information on human brain growth a quarter century ago, it was impossible to map the sequential changes in behavior and abilities on a maturing brain. As a result, it was easy for psychologists to argue that experience was the primary determinant of new actions, cognitive abilities, and moods. Piaget (1950) argued that infants’ actions in and on the world created psychological structures that made it possible for 8-month-olds to reach toward the location where an adult had hidden an attractive toy seconds earlier. We now believe that the successful retrieval of the hidden toy requires the maturation of the hippocampus, medial temporal lobe, prefrontal cortex, and their interconnections. No amount of sensory–motor experience would permit a 4-month-old to reach to the correct location.

The degree of determinacy in the relation between a psychological product and a pattern of neural activity is controversial and the debate on this issue has some of the features of a culture war. Some neuroscientists believe that, given access to the total pattern of brain activity in a person at a particular moment, they could, in principle, predict exactly what thought or feeling would be experienced, or what behavior might be implemented in the next moment. An equal number of more skeptical biologists see only probability distributions defining the relations between brain and psychological states. The probability of an eye blink occurring to a puff of air applied to the cornea (the puff activates neurons that project to eye muscles) is very high. But the probability of a facial grimace to a drop of lemon juice placed on the tongue (due to activation of the neurons that project to the muscles of the face) is lower. Lower, still, is the probability that a child will become immobile on seeing a large spider on a table (due to activation of the amygdala) because the child’s prior history with spiders, and related expectations, determine whether the prefrontal cortex will or will not modulate the amygdala’s projections to brain stem sites.

Experience could make one person’s semantic network for “chocolate chip cookies” emphasize the semantic nodes for “mother,” “oven,” and “dinner,” whereas the primary nodes for another might be “a friend,” “restaurant,” and “lunch.” But the neuronal ensembles underlying these two different networks could involve exactly the same neurons in temporal and other cortical associational areas. Thus, a neuronal ensemble can represent different psychological forms in different individuals. This possibility implies that psychological structures have some autonomy and cannot be discovered with neuroscience evidence alone. One needs, in addition, information on the individuals’ past history.

When future neuroscientists can measure the electrochemical events occurring in a pair of synapsing neurons they will probably discover that these microprocesses are loyal to the assumptions of quantum mechanics. Should this prediction prove valid, there will be a necessary indeterminacy at every synapse, and, therefore, lack of perfect predictability between the brain’s reaction to a particular incentive and a psychological outcome (Lau, Roger, Haggard, & Passingham, 2004).

Many social scientists resist the strong form of determinism found in the writings of some neuroscientists because they know that each agent’s prior experiences—both recent and from the distant past—play a critical role. It is always necessary to state the conditions under which a relation between brain activity and a psychological outcome holds. The amplitudes of the sequential event-related potential (ERP) waveforms to the same olfactory stimulus changed when participants were tested three times over a 12-day interval (correlations ranged from 0.4 to 0.7) because their expectations on the second and third sessions were different from those on the first session (Welge-Lussen, Wille, Renner, & Kobal, 2003). Neurons in both the anterior and posterior portions of the orbitofrontal prefrontal cortex become active when a person receives a squirt of chocolate milk. However, the anterior neurons stop responding when the person has been sated on the chocolate milk and finds its taste unpleasant, although the posterior neurons continue to respond (Kringelbach, O’Doherty, Rolls, & Andrews, 2003).

If the brain’s reactions to olfactory and taste stimuli are affected by past experience, we can be certain that this influence is more dramatic for complex events with a rich network of associations. For example, the brain generates a distinct negative waveform at 170 msec to a human face (called the N170 because it has a negative polarity and usually occurs with a latency of 170 msec), but not to a pair of black dots enclosed within a circle. However, the N170 does occur if the pair of black dots is presented after the participant has seen a series of schematic faces and, therefore, anticipates the presentation of a face.

There is no consensus on how to conceptualize a psychological property, like a competence or an emotion. One position conceives of a psychological property as a permanent brain state always ready to influence behavior, much like a hand that is always capable of picking up an object. The less popular view regards a psychological property as a temporary state whose actualization depends on the context and the brain state at the moment. This difference is captured by the different meanings of the following two sentences:

1. Mary is an anxious person.
2. Mary has the capability for feeling anxious if criticized by a stranger.

Because an agent’s expectations are a function of life history, and it is usually impossible to know that history, there is some indeterminacy in the relation between an incentive, on the one hand, and the brain’s reaction and subsequent psychological product, on the other. Therefore, the verb “enable” is more appropriate than “cause” when we think about the relation between brain activity and a psychological reaction. Even as vocal a defender of biological determinism as E. O. Wilson (1999) agreed that, “There can be no simple determinism of human thought. . . because the individual mind can not be fully known. . . the self can go on believing in its own free will” (p. 131). This book assumes neither a fixed determinism between brain activity and a psychological product nor the equally extreme view that psychological development is independent of brain growth. We recognize that the middle ground is rarely popular in most controversies, but urge readers to maintain a tolerance for ambiguity as they reflect on the extensive corpus of facts scientists have discovered.

How to Conceptualize Brain and Behavior

We can select at least four different ways to structure the phenomena that define biological and behavioral development. The most desirable relies on theory as a guide. Physicists work with that advantage because they possess rigorous theory describing functional relations among concepts like mass, electron, energy, force, magnetism, and entropy. Thus, the organization of physics textbooks is determined by the nature of the theoretical relation, and the phenomena of friction and heat are separate from the quantum events of photons and quarks.

Unfortunately, neither neuroscientists nor developmental psychologists possess robust theory. Both disciplines are still trying to understand how brains enable human thought, feeling, and behavior. As a result, scholars exploit three other guides for organization: (a) comparison with an ideal, (b) shared features, and (c) a common history.

Ideal Forms. Most scientists, including psychologists and neuroscientists, hold notions of ideal forms. The neuroscientists often write as if the brain of the 20-year-old possesses optimal properties. For example, they note that the sensory areas of 3-month-olds contain 150% of the number of synapses of the 20-year-old. Psychologists, too, assume the young adult is the ideal when they claim that a 5-year-old has a poorer retrieval memory and less control over action than a college student.

This perspective assumes that the child and the elderly are less perfect forms. Although 19th-century biologists assumed that humans were the acme of evolution, most contemporary biologists acknowledge that the human species happens to have some qualities that are more, and some that are less, adaptive for their niche.

Shared Properties. Neuroscientists and psychologists often exploit a second strategy which relies on shared observable features. The former group considers neurons with the same shape (for example, pyramidal neurons), same class of receptor, or same location, as belonging to a common category. The psychologist is more slavishly devoted to this rule because of the inability to measure brain states in natural settings. Thus, all acts that mimic another are called imitation, all acts that hurt another are called aggressive, and all acts that help another are called altruistic. Unfortunately, psychologists are prone to use performance on one procedure as the basis for a broad category of competence. One of the most egregious errors made in clinical settings is to categorize the child as having “impaired memory functioning” simply because of a low score on the digit recall scale of the Wechsler Intelligence Scale. The correlations among recall memory for numbers, recognition memory for scenes, and implicit memory for words are so low it is a mistake to treat performance in any one situation as representing a child’s memorial talents.

One serious problem with treating similarity in a single feature as a basis for a common category is that acts that are similar in appearance often have different antecedents and, therefore, different meanings. A 2-day-old infant will protrude his or her tongue when an adult, bending over the infant, displays that action. But this newborn response should not be placed in the same category with a 4-year-old’s attempt to bake a cake alongside her mother. An infant’s striking a parent should not be classified with an adolescent’s murder of a peer at a street corner, or a mouse biting an intruder. Similarly, most physiological events are due to different antecedent conditions; for example, high vagal tone in a laboratory could be the product of restlessness, a relaxed mood, or an extreme degree of attentiveness to events in a testing room.

Because a particular behavior can be derived from different biological states, there are fewer classes of behavior than classes of brain states. This asymmetry is present in our language. Behaviors are described with predicates and there are fewer predicates with distinctive meanings than words for different agents or contexts. A person bites a cookie when eating, a thread when sewing, and a cellophane wrap when opening a gift. The word “bite” has different meanings in these three contexts because the intention and the brain state are distinct. Thus, the sentences, “the mouse bit the intruder animal” and “the infant bit her mother” have different meanings. But because English has only one predicate for this act, the word “bite” is used to describe both events.

Neuroscientists often borrow words intended originally to describe human psychological states and apply them to animals, with the tacit assumption that important features of the word’s meaning remain unchanged. For example, some scientists attribute “fear” to a mouse who stays in a dark area and does not enter a brightly lit one, but would not attribute “love” to a pair of copulating mice, or “pride” to a bird who had completed construction of a nest. Fear, love, pride, and a host of other words intended to describe human emotional states should not be indiscriminately applied to animals. New terms must be invented.

The understandable desire to minimize the psychological differences between humans and other animals serves the rational desire to use the evolutionary principle of inclusive fitness to explain human behaviors and social institutions. For example, some primatologists believe that capuchin monkeys understand the semantic concept “inequity” because they behave in a distinct way when they receive less tasty food than another animal a few feet away (Brosnan & de Waal, 2003). However, differential behavior to two distinct events is insufficient evidence to infer a semantic concept as abstract as “inequity.” Otherwise, scientists should award male monkeys possession of the semantic concept “estrus” because the animals behave in different ways when a female is or is not sexually receptive. Although many human sensory, motor, and physiological competences have legitimate analogs in other animals, unique properties often occur in evolution—flight in birds and internal fertilization in mammals are two examples.

There are at least three reasons why many scientists search enthusiastically for animal behaviors that seem to share essential features with human language, morality, inference, and consciousness. The usual argument is that all vertebrates have strings of DNA on their chromosomes that are responsible for the proteins that comprise the tissues and organs that many species share. Hence, it is reasonable to assume that the neural bases for the behaviors of mice and rats will resemble those that mediate behaviors serving similar functions in humans. A second legitimate argument is that scientists can perform experiments with animals that are impossible with humans and the results of this work might illuminate the human condition. Harry Harlow’s (1966) research with isolated infant monkeys was celebrated because the abnormal development of infant rhesus separated from their mothers and placed with inanimate objects implied that a similar outcome would hold for human infants. This discovery provided support for the popular assumption that human infants required intimate contact with their adult caretakers.

A less rational, but nonetheless attractive, reason for generalizing from animals to humans is that this view rationalizes the human qualities of aggression, selfishness, and multiple sex partners. These, and other ethically questionable tendencies, provoke a little guilt in some humans. However, if humans and chimpanzees share a common biology and psychology, perhaps humans should not feel ashamed or bothered by these motives and actions.

Finally, the assumption of biological proximity lends tacit support to the strong wish for a seamless unity among all living things. Many adults in contemporary societies would like to believe that humans could be a band of brothers and sisters, sharing common motives, values, emotions, and talents. Because the current strife across the world frustrates this idealistic hope, it is reassuring to believe that humans, chimpanzees, and monkeys might be “brothers under the skin.” However, it is worth noting that biologists who study varied bird species have not tried to find the anlage of flight, imprinting, or seasonal migration in crocodiles, snakes, or lizards because they know that these characteristics are novel evolutionary features that have no analogue among reptile species.

The human brain has a number of sufficiently distinct features to suggest that the relations between brain and behavior in rats, monkeys, and humans are not the same for many psychological processes. Even rats and cats behave differently during a 3-min delay between the appearance of a conditioned stimulus signaling food and food delivery (Bos, Meijer, Van Renselaar, van der Harst, & Spruijt, 2003). Flax is a poor model for Mendelian genetics, the spider is a poor model for mammalian reproductive physiology, and the mouse and monkey may not be useful models for all human properties. This claim is especially valid for language, inference, consciousness, and morality.

Although classification of forms based on a single feature remains a frequent strategy, individuals who share a single characteristic are usually heterogeneous with respect to other qualities that should be added to the shared feature. One of the most useful sources of supplementary information comes from the individual’s past.

Shared History. Shared history is a useful criterion to guide organization. The cladists in evolutionary biology use common ancestor forms to classify a contemporary animal group. Terriers and wolves are classed together because the former evolved from the latter. Terriers and Siamese cats are not placed in the same category, although they are more similar in size, tameness, and usual location.

Neuroscientists rely on origins when they study the derivatives of the neural crest cells, which have different final functions and locations in the newborn. Psychologists group together all adults who had been securely attached infants, abused children, or grew up in poverty, on the assumption that the members of each of these groups share significant features. The danger in this strategy is to ignore the differences between adults who share a contemporary feature but have different histories. For example, depressed adults whose first episode occurred before age 20 differ from those whose first bout of depression occurred after that age. The depressive mood of the former group is more chronic and responds less favorably to drug treatment (Stewart, Bruder, McGrath, & Quitkin, 2003).

Multiple Criteria. Ideal states, shared features, and common histories have both advantages and disadvantages as criteria. Hence, neuroscientists and psychologists exploit two or all three. The biological concept of species, for example, rests on similarity in contemporary features as well as evolutionary history. The classification of neurotransmitters relies on similarity in molecular structure, as well as their effects on p...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Dedication
• Contents
• Preface
• 1 Brain and Behavioral Development
• 2 Prenatal Development
• 3 Birth to 6 Months
• 4 The Second Transition: 7 to 12 Months
• 5 The Second Year
• 6 2 to 8 Years
• 7 Reflections
• References
• Author Index
• Subject Index