Sarah-Jayne Blakemore

Adolescence: a foundation for future health.

Adolescence is a life phase in which the opportunities for health are great and future patterns of adult health are established. Health in adolescence is the result of interactions between prenatal and early childhood development and the specific biological and social-role changes that accompany puberty, shaped by social determinants and risk and protective factors that affect the uptake of health-related behaviours. The shape of adolescence is rapidly changing-the age of onset of puberty is decreasing and the age at which mature social roles are achieved is rising. New understandings of the diverse and dynamic effects on adolescent health include insights into the effects of puberty and brain development, together with social media. A focus on adolescence is central to the success of many public health agendas, including the Millennium Development Goals aiming to reduce child and maternal mortality and HIV/AIDS, and the more recent emphases on mental health, injuries, and non-communicable diseases. Greater attention to adolescence is needed within each of these public health domains if global health targets are to be met. Strategies that place the adolescent years centre stage-rather than focusing only on specific health agendas-provide important opportunities to improve health, both in adolescence and later in life.

Abnormalities in the awareness of action

Optimal motor control relies on internal representations of the actual, desired and predicted states of our limbs and the external world. Only certain components of these internal representations are available to awareness. We suggest that impairments of the components of internal representations might underlie a broad variety of neuropsychiatric symptoms, including the anarchic hand sign, phantom limbs, utilization behaviour and delusions of control.

Explaining the symptoms of schizophrenia: Abnormalities in the awareness of action

We propose that the primary cognitive deficit associated with delusions of control is a lack of awareness of certain aspects of motor control. This problem arises because of a failure in the mechanism by which the predicted consequences of an action are derived from a forward model based on the intended sequence of motor commands. This problem leads to a number of behavioural consequences, such as a lack of central error correction, many of which have been observed in patients with delusions of control and related symptoms. At the physiological level, delusions of control are associated with over-activity in parietal cortex. We suggest that this over-activity results from a failure to attenuate responses to sensations of limb movements even though these sensations can be anticipated on the basis of the movements intended. The lack of attenuation may arise from long range cortico-cortical disconnections which prevent inhibitory signals arising in the frontal areas which generate motor commands from reaching the appropriate sensory areas.

Why can't you tickle yourself?

It is well known that you cannot tickle yourself. Here, we discuss the proposal that such attenuation of self-produced tactile stimulation is due to the sensory predictions made by an internal forward model of the motor system. A forward model predicts the sensory consequences of a movement based on the motor command. When a movement is self-produced, its sensory consequences can be accurately predicted, and this prediction can be used to attenuate the sensory effects of the movement. Studies are reviewed that demonstrate that as the discrepancy between predicted and actual sensory feedback increases during self-produced tactile stimulation there is a concomitant decrease in the level of sensory attenuation and an increase in tickliness. Functional neuroimaging studies have demonstrated that this sensory attenuation might be mediated by somatosensory cortex and anterior cingulate cortex: these areas are activated less by a self-produced tactile stimulus than by the same stimulus when it is externally produced. Furthermore, evidence suggests that the cerebellum might be involved in generating the prediction of the sensory consequences of movement. Finally, recent evidence suggests that this predictive mechanism is abnormal in patients with auditory hallucinations and/or passivity experiences.

The role of puberty in the developing adolescent brain.

Adolescence refers to the period of physical and psychological development between childhood and adulthood. The beginning of adolescence is loosely anchored to the onset of puberty, which brings dramatic alterations in hormone levels and a number of consequent physical changes. Puberty onset is also associated with profound changes in drives, motivations, psychology, and social life; these changes continue throughout adolescence. There is an increasing number of neuroimaging studies looking at the development of the brain, both structurally and functionally, during adolescence. Almost all of these studies have defined development by chronological age, which shows a strong—but not unitary—correlation with pubertal stage. Very few neuroimaging studies have associated brain development with pubertal stage, and yet there is tentative evidence to suggest that puberty might play an important role in some aspects of brain and cognitive development. In this paper we describe this research, and we suggest that, in the future, developmental neuroimaging studies of adolescence should consider the role of puberty. Hum Brain Mapp, 2010.

The perception of self-produced sensory stimuli in patients with auditory hallucinations and passivity experiences: evidence for a breakdown in self-monitoring

BACKGROUND To test the hypothesis that certain psychotic symptomatology is due to a defect in self-monitoring, we investigated the ability of groups of psychiatric patients to differentiate perceptually between self-produced and externally produced tactile stimuli. METHODS Responses to tactile stimulation were assessed in three groups of subjects: schizophrenic patients; patients with bipolar affective disorder or depression; and normal control subjects. Within the psychiatric groups subjects were divided on the basis of the presence or absence of auditory hallucinations and/or passivity experiences. The subjects were asked to rate the perception of a tactile sensation on the palm of their left hand. The tactile stimulation was either self-produced by movement of the subjects right hand or externally produced by the experimenter. RESULTS Normal control subjects and those psychiatric patients with neither auditory hallucinations nor passivity phenomena experienced self-produced stimuli as less intense, tickly and pleasant than identical, externally produced tactile stimuli. In contrast, psychiatric patients with these symptoms did not show a decrease in their perceptual ratings for tactile stimuli produced by themselves as compared with those produced by the experimenter. This failure to show a difference in perception between self-produced and externally produced stimuli appears to relate to the presence of auditory hallucinations and/or passivity experiences rather than to the diagnosis of schizophrenia. CONCLUSIONS We propose that auditory hallucinations and passivity experiences are associated with an abnormality in the self-monitoring mechanism that normally allows us to distinguish self-produced from externally produced sensations.

Is Adolescence a Sensitive Period for Sociocultural Processing

Adolescence is a period of formative biological and social transition. Social cognitive processes involved in navigating increasingly complex and intimate relationships continue to develop throughout adolescence. Here, we describe the functional and structural changes occurring in the brain during this period of life and how they relate to navigating the social environment. Areas of the social brain undergo both structural changes and functional reorganization during the second decade of life, possibly reflecting a sensitive period for adapting to ones social environment. The changes in social environment that occur during adolescence might interact with increasing executive functions and heightened social sensitivity to influence a number of adolescent behaviors. We discuss the importance of considering the social environment and social rewards in research on adolescent cognition and behavior. Finally, we speculate about the potential implications of this research for society.

Action prediction in the cerebellum and in the parietal lobe

The ability of the central nervous system to predict motor behaviour is a central issue in experimental and computational studies of motor control. The parietal cortex and the cerebellum have been proposed to play a role in sensorimotor prediction. Here we discuss the roles of these two brain regions in various aspects of sensorimotor prediction according to results of recent empirical studies using a variety of techniques including electrophysiology, psychophysics, functional neuroimaging and the investigation of neurological patients.

Self-awareness and action

In this review we discuss how we are aware that actions are self-generated. We review behavioural data that suggest that a prediction of the sensory consequences of movement might be used to label actions and their consequences as self-generated. We also describe recent functional neuroimaging experiments and studies of neurological and psychiatric patients, which suggest that the parietal cortex plays a crucial role in the awareness of action.

Social cognitive development during adolescence

Social relationships are particularly important during adolescence. In recent years, histological and MRI studies have shown that the brain is subject to considerable structural development during adolescence. Brain regions that are implicated in social cognition, including parts of prefrontal, parietal and superior temporal cortex, undergo the most pronounced and prolonged change. However, the development of social cognition during adolescence and its neural underpinnings remains poorly understood. Here, we begin by outlining how the brain changes between childhood and adulthood. We then describe findings that have emerged from behavioural and neuroimaging studies of the recognition of facial expression during adolescence. Finally, we present new data that demonstrate development of emotional perspective taking during adolescence. In this study, 112 participants, aged 8-36 years, performed a computerised task that involved taking an emotional perspective either from the participants own point of view or from that of another person. The results showed that average difference in reaction time (RT) to answer questions in the first person perspective (1PP) and third person perspective (3PP) significantly decreased with age. The RT difference of adults tended to cluster close to the zero line (3PP = 1PP), while a greater proportion of pre-adolescents had higher difference values in both the positive (3PP > 1PP) and negative direction (1PP > 3PP) of the scale. The data suggest that the efficiency, and possibly strategy, of perspective taking develop in parallel with brain maturation and psychosocial development during adolescence.