INTRODUCTION

Psychophysiology is the study of the relation between psychological events and biological processes in human participants. The electrocardiogram (ECG) and heart rate (HR) have been commonly used measures throughout the history of psychophysiological research. Early studies found that stimuli eliciting differing emotional responses in adults also elicited HR responses differing in magnitude and direction of change from baseline (e.g., Darrow, 1929; Graham & Clifton, 1966; Lacey, 1959). Vast improvements in methods of measuring ECG and knowledge regarding the relation between HR and cognitive activity have occurred.

Heart rate has been particularly useful in developmental psychophysiological research. Researchers interested in early cognitive and perceptual development have utilized HR as a window into cognitive activity for infants before they are capable of demonstrating complex behaviors or providing verbal responses. Also, the relation between brain control of HR and the behavior of HR during psychological activity has helped work in developmental cognitive neuroscience. In this chapter, we address the use of the ECG and HR in research on infants. We review three ways in which HR has been used in psychophysiological research: HR changes, attention phases defined by HR, and HR variability (particularly respiratory sinus arrhythmia). Topics we focus on are the areas of the brain that are indexed with these measures, developmental changes associated with these measures, and the relation of these measures to psychological processes. Before covering research with infants, we briefly review background information on the heart, the ECG and HR, and its relation to psychophysiology.

INTRODUCTION

The study of social and emotional development presents multiple complexities to the researcher. For instance, infants and young children cannot provide verbal report of their feeling states or moods, and researchers often rely on questionnaire measures given to parents or caregivers regarding the social or emotional behavior of the child. In addition, stimuli that elicit emotions in infants and young children are often age specific and the potency of these stimuli depends upon the context in which they are presented. The ability to present still pictures or video stimuli designed to elicit emotion (as is often done in adult studies) is compromised by the infant or young child's ability to attend to the stimulus, and more particularly by their ability to interpret or understand the nature of the stimuli. Finally, infants and young children display a good deal of motor behavior in response to events that elicit emotion. Such motor activity is particularly problematic for the recording of physiological responses, which are often subject to motor artifact. These issues are certainly not specific to the study of social and emotional development, and are also faced by researchers interested in cognitive as well as social and emotional development. Lack of verbal report, interpretation of stimulus characteristics, importance of context, variations in state and motor reactivity are all general problems faced in the study of infants and young children.

The field of cognitive and affective neuroscience has burgeoned during the last 20 years, prompting the publication of several handbooks. The allied field of psychophysiology included two such comprehensive collections over the last 7 years but, surprisingly, only one chapter in each was dedicated to issues pertaining mainly to children (Fox, Schmidt, & Henderson, 2000; Fox, Schmidt, Henderson, & Marshall, 2007) as was the case some 20 years earlier (Porges & Fox, 1986).

Today, there has been considerable research attention directed toward understanding brain-behavior relations in a developmental context. Interdisciplinary approaches to the study of behavior in which development and brain are interfaced have blossomed. We now routinely observe researchers in developmental psychology interacting with people in the fields of behavioral and cognitive neuroscience, and vice versa. This book reflects the spirit of the multidisciplinary nature of science and the dialogue of our two disparate worlds: one as a social developmental psychologist (LAS) and the other as a cognitive neuroscientist (SJS).

The seeds for this book were sown five years ago as a result of our frequent discussions of science, life, and the human condition. In addition to the friendship that quickly developed from our many talks over the years, there soon emerged the realization that, although more and more developmental child psychologists were beginning to study brain-behavior relations in a developmental context, a lack of resources in the area from which they could draw was apparent.

INTRODUCTION

The measurement of electrodermal activity (EDA) or palmar sweat gland activity in children involves many of the same issues as in adults. There are, however, some special problems that can arise with children, all of which are inversely proportional to age. The most fundamental problem has to do with possible differences in which stimuli elicit electrodermal responses. This topic has not been well researched, but infants and toddlers appear to respond to a more restricted range of stimuli and children may not respond to some stimuli as well as adults do. The second problem has to do with difficulties in timing the presentation of stimuli, especially in toddlers and very young children for whom compliance with experimental instructions is substantially less than for older children and adults. A third problem, also related to problems with compliance, is managing the stress associated with attaching electrodes in a strange laboratory setting. This chapter will begin with the nature and measurement of the electrodermal effector system, followed by the problems specific to children.

For readers interested in a more thorough coverage of this topic than is provided by the present chapter, there are a number of reference sources. Introductions to psychophysiology, including EDA, are available in the texts by Stern, Ray, and Quigley (2001) and Hugdahl (1995). Consensus recommendations for how to record EDA are offered by Fowles and colleagues (1981).

INTRODUCTION

Visual abilities undergo major transformation during infancy and childhood. Although infants arrive in the world both able to see and to learn about what they see, many aspects of vision and visual cognition continue to develop well into childhood (e.g., Chung & Thomson, 1995; Lewis & Maurer, 2005). Event-related potentials (ERPs) are a useful tool for investigating the neurophysiological correlates of these developmental changes as they can provide information not available from behavioral measures alone. In particular, they provide precise information about the timing and some information about the spatial distribution of the brain events underlying visual processing. Since ERPs can be obtained in “passive” tasks, where participants simply look at visual displays without any requirement to make a verbal or behavioral response, they allow use of the same procedure across a wide range of age and ability levels. For example, visual ERPs have been used to study face processing in infants only a few months old (e.g., Halit, de Haan, & Johnson, 2003) and have been used to investigate aspects of visual processing in children with various developmental disorders, including autism spectrum disorder (e.g., Dawson et al., 2002; Kemner, van der Gaag, Verbaten & van Engeland, 1999), Down syndrome (e.g., Karrer et al., 1998), and attention deficit-hyperactivity disorder (reviewed in Barry, Johnstone, & Clarke, 2003). Along with these distinct advantages, however, ERPs also present challenges both in terms of experimental design and data collection, and analysis and interpretation.

INTRODUCTION

A sudden noise occurs while you are concentrating and you respond quickly and automatically – your body muscles flex, your eyes blink, and your facial expression registers a grimace of surprise. You have just experienced a startle reflex. The startle reflex (or startle response) is commonly measured in research studies by a blink response in humans, elicited by some startling stimulus such as a loud noise. The blink response is an early and reliable component of startle in humans. It occurs to stimuli in various sensory modalities (e.g., auditory, visual, cutaneous) and often begins within 30 ms after the onset of a sudden and intense stimulus.

The word “reflex” often seems to bring to mind a stable, simple, and unchanging response elicited under specific circumstances. But in the case of the startle reflex, this view is overly simplistic. Though this reflex can be reliably elicited, it turns out to also be highly modifiable by an extensive variety of stimuli, circumstances, and clinical conditions. The wide range of studies examining this process of modification is generally referred to as startle modification research. Fundamentally, the paradigms employed in this research involve situations in which the startle reflex is modulated or modified in amplitude, latency, or probability by another non-startling variable of interest. The remarkably wide range of factors that can modify startle is what has generated such a broad interest in its study.

INTRODUCTION

Developmental psychophysiological research is a relatively young field that is rapidly expanding partly because sophisticated, cost-effective technology now allows researchers to collect physiological data much more efficiently and effectively. This volume of developmental psychophysiology reflects both the newness as well as the growth of the field. As alluded to by many of the authors included in this volume, researchers collecting valid psychophysiological data in children face challenges that are magnified when compared to the collection of these same data in adults. However, developmental psychophysiologists are not alone in addressing these challenges as we can readily draw upon the experiences from specialists working in other related fields.

The fields of psychology and education have also contributed to our general knowledge about effective methods of assessing children. Notably, the number of texts written on behavioral and neuropsychological assessment of children is plentiful, and we can apply this knowledge to assessment of psychophysiological information as well. For example, the recent editions of assessment of children (Sattler 2001, 2002) comprehensively discuss skills necessary for test administrators to have in order to successfully assess children. Some of these skills include effective listening, building rapport with the child, and how to handle difficult behaviors and individual temperaments. A researcher who develops these assessment skills discussed by psychologists, neuropsychologists, and education professionals, along with the technical skills necessary for obtaining the desired psychophysiological measurements will be much more successful in obtaining reliable and valid research data.

INTRODUCTION

The field of developmental psychophysiology provides the methodology for examination of age-related changes in the functioning of the brain. The electroencephalogram (EEG) is an efficient, non-invasive, and relatively inexpensive method for studying brain development in infants and children and for relating brain development to changes in cognitive behaviors. Utilizing EEG allows for examination of these developmental changes without dramatic interference with normal ongoing behaviors. All of these characteristics make the EEG one of the more favorable methods for investigating brain-behavior relations with young populations (Casey & de Haan, 2002; Taylor & Baldeweg, 2002).

The EEG discussed in this chapter is sometimes called “quantitative EEG” and is used for basic research on brain activity during cognition or emotion and for basic research on brain maturation. Typically, quantitative EEGs used for basic research are digital records that are converted from the time domain to the frequency domain by means of spectral analysis, yielding spectral power at specific frequencies, or by means of phase coherence analysis, yielding the degree to which the EEG signals at two distinct scalp locations are in phase at a specific frequency. This quantitative methodology differs from the traditional use of the EEG in the clinical setting to localize seizures or tumors. It also differs from event-related potentials, or ERPs, which are brain electrical responses that are time locked to a specific set of stimuli. ERP methodology and research is reviewed in Chapters 2, 3, and 4 of this volume.

CONCEPTUAL FRAMEWORK

Recently, event-related neuroelectric oscillations have provided important tools with which to study information processing in the brain and with which to enrich our knowledge of brain maturation and cognitive development. The essential advantages of this approach are the ability to (1) analyze neuroelectric responses reflecting mechanisms of stimulus information processing in comparison to electrical activity in a passive state reflecting the neurobiological maturation of the brain; (2) refine electrophysiological correlates of information processing by separating functionally different but simultaneously generated responses from different frequency ranges; and (3) reveal differential developmental dynamics of the power and synchronization of neuroelectric responses, thus providing information about independent neurophysiological mechanisms during biological and cognitive development.

In this chapter, the conceptual background of event-related oscillations will be presented with a major focus on their relevance for developmental research, followed by methods, analytic tools, and parameters for assessment of event-related oscillations. Finally, major findings on the development of the delta, theta, alpha, and gamma response systems in the brain will be described.

EVENT-RELATED POTENTIALS

The electroencephalogram (EEG) is a time-varying signal reflecting the summated neuroelectric activity from various neural sources in the brain during rest or functional activation. An EEG response that occurs in association with an eliciting event (sensory or cognitive stimulus) is defined as an event-related potential (ERP). However, the ERP may contain EEG activity not related to specific event processing, as well as electric activity from non-neural sources.

The prerequisite for discussing changes in responsiveness and sculpting inhibitory processes of neocortical neurons during different behavioural states (see Chapters 6 and 7) is the description of various neuronal types and their functional properties, which is the subject of this chapter.

Varieties, immunoreactivity and connectivity of neocortical neuronal classes

The mammalian neocortex is a laminated structure that contains up to 28 × 109 neurons that are connected by about 1012 synapses. The attempt to simplify the functional complexity of the neocortex started with the description of the columnar organization into modules that have a basic similarity of internal design and operation (see Mountcastle, 1997, 1998). The neocortex consists of a large population of long-axon (output) neurons that are excitatory and reciprocally connected to each other in the same and/or opposite hemisphere as well as to thalamocortical (TC) neurons, and a smaller population of local-circuit inhibitory neurons.

Besides morphological techniques that distinguish these two neuronal classes (Figures 2.1–2.3), physiological identification of output neurons is possible using antidromic and orthodromic activations (Figures 2.4 and 2.5), which determine the sources of synaptic inputs and neuronal targets (Evarts, 1964, 1965; Steriade et al., 1974a) thus leading to systematizations with a limited number of neuronal categories. These are rather difficult techniques in behaving animals; with some exceptions (Steriade et al., 2001a, b), they are rarely used nowadays. Neocortical neurons have been classified into four categories according to their intrinsic electrophysiological properties, as determined by responses to intracellular current pulses (see Section 2.3).