Friedhelm C. Hummel and Leonardo G. Cohen
This article explains the role of brain stimulation in neurorehabilitation. The outline of this article is formed by the characterization of some of the problems faced in the field of nuerorehabilitation. Furthermore, it describes results of studies conducted to understand the functional changes in the motor cortices of hemispheres after stroke. This article finally discusses some of the interventional approaches proposed to improve motor function. Stroke is the main cause of long-term disability among adults. The disability resulting from stroke impairs the quality of life. Post-stroke recovery remains an important clinical focus. Various modalities of brain have been proposed as strategies to enhance motor function when combined with conventional neurorehabilitative interventions after a stroke. Before these approaches can reach the clinic, their results need to be replicated in larger samples and controlled conditions to determine their value.
Lynn M. Maher
Broca’s aphasia serves as a platform for discussions of the cognitive and neural mechanisms of sentence production and how those systems break down in individuals with damage in left inferior frontal regions beyond Broca’s area, suggesting a role for such regions in syntactic processing. Standardized and nonstandardized diagnostic tools facilitate assessment of comprehension and production of grammatical functions that can be impaired in Broca’s aphasia. Several treatment approaches address impairment in sentence production that emanates across various processes in sentence formulation. The nomenclature surrounding Broca’s aphasia provides a launching pad to guide analysis and intervention for the communication impairments experienced by these individuals.
Joseph Classen and Katja Stefan
This article reviews several protocols of repetitive transcranial magnetic stimulation (rTMS)-induced plasticity. rTMS, when applied to the motor cortex or other cortical regions of the brain, may induce effects that outlast the stimulation period. The neural plasticity, which emerges as a result of such interventions, has been studied to gain insight into plasticity mechanisms of the brain. In two protocols the structure of rTMS trains is modified, informed by the knowledge of the physiological properties of the corticospinal system. Pulse configuration, stimulus frequency, stimulus intensity, the duration of the application period, and the total number of stimuli are some variables that have to be taken into account when reviewing the physiological effects of rTMS. This article also introduces the concept of patterned rTMS pulses and rTMS with ischemic nerve block. In addition, rTMS has raised considerable interest because of its therapeutic potential; however, much needs to be done in this field.
This article establishes the concept of a methodological approach to combine brain imaging with brain stimulation. Transcranial magnetic stimulation (TMS) is a tool that allows perturbing neural activity, in time and space, in a noninvasive manner. This approach allows the study of the brain-behaviour relationship. Under certain circumstances, the influence of one region on other, called the effective connectivity, can be measured. Functional connectivity is the extent of correlation in brain activity measured across a number of spatially distinct brain regions. This tool of connectivity can be applied to any dataset acquired with brain-mapping tools. However, its interpretation is complex. Also, the technical complexity of the combined studies needs to be resolved. Future studies may benefit from focusing on neurochemical transmission in specific neural circuits and on temporal dynamics of cortico-cortical interactions.
Sven Bestmann, Christian C. Ruff, Jon Driver, and Felix Blankenburg
Transcranial magnetic stimulation is used for a wide range of applications in cognitive, clinical, and neuroscience. However, the precise physiological mechanisms by which TMS influences brain function are only partially understood. Combining TMS with functional magnetic resonance imaging (fMRI) provides a more complete picture of the neural underpinnings of TMS effects. This article gives an overview of methodology and technical aspects concerned with combining TMS with fMRI. Furthermore, it explains the challenges involved with the combination of TMS with fMRI and proposes solutions to the same. It also focuses on recent applications of concurrent TMS-fMRI. Combining TMS with fMRI may allow a new noninvasive probe technique for the human brain. TMS-fMRI can be used to compare TMS-evoked effective connectivity in health and disease. It can potentially be used to investigate connectivity changes during different states, with different degrees of involvement for interconnected brain regions during different tasks.
Cees van Leeuwen
Visual perception requires parallel processing of distributed information. To achieve true parallelism, in which multiple patterns can be processed simultaneously, dynamic synchronization in ongoing, oscillatory brain activity plays a crucial role. On a large time scale, it can help create and maintain an optimal brain connectivity structure that is clustered, modular, and connected. Over a range of shorter time scales, dynamic synchrony is instrumental in coordinating and controlling the flow of information in the brain. Dynamic synchronization modulates in a pulsed manner the receptivity of sensory systems, the effectivity of neural communication and the binding of visual stimulus information. Collectively, these processes control communication in the brain and determine what we experience.
Alexander Wolters, Ulf Ziemann, and Reiner Benecke
The cortical silent period (cSP) refers to an interruption of voluntary muscle contraction by transcranial stimulation of the contralateral motor cortex. This article summarizes the physiology of cSP and gives guidelines as to how the cSP should be recorded and analysed, and refers to useful clinical applications. It describes the mechanisms at the spinal and supraspinal level can account for the cSP. It is currently thought that the cSP is mediated by gamma-aminobutyric acid receptors. cSP measurements are easy to obtain but require a standardized protocol to allow useful interpretation. Conditioning electrical stimulation of cutaneous nerves shortens the cSP. A conditioning transcranial magnetic stimulation pulse also affects cSP duration. The cSP duration is influenced by pathological conditions. cSP is an attractive probe to assess motor cortical inhibition in health and disease.
Tetsuya Iidaka and Tokiko Harada
This chapter reviews how cultural values modulate emotional processing in the amygdala? Here we discuss a functional magnetic resonance imaging experiment whereby Japanese participants performed an emotional dot-probe task in which they were presented with an unpleasant picture (insect) and a neutral picture (chair). The unpleasant picture condition evoked a greater amygdala response. Between-condition differences in amygdala response were negatively correlated with individualism and collectivism cultural value scores, indicating that individuals who were more collectivistic showed a greater amygdala response. In a second experiment, we modulated individual cultural differences (individualism vs. collectivism) with a cultural priming task in Japanese participants, half of whom were primed with an individualistic scenario and half with a collectivistic scenario. Significant activation of the right amygdala was observed in the collectivistic-primed group. Biological variability in responses to emotional stimuli exists in individuals living in a relatively unitary culture, such as Japan; the neural response of the amygdala was significantly associated with the cultural values of individualism and collectivism.
Design and analysis of motor-evoked potential data in pediatric neurobehavioral disorder investigations
Donald L. Gilbert
This article discusses how transcranial magnetic stimulation (TMS) can be used to study the pathophysiological substrata of pediatric neurological and neurobehavioural disorders and to provide practical guidance for future research. It outlines the substantial challenges inherent in studying in vivo the neurobiology of pediatric neurobehavioural disorders, such as safety, quantitative versus categorical measures, and challenges in correlational studies. It discusses ways in which TMS generates quantitative measures that may function as endophenotypes for neurobehavioural disorders. Combining TMS with other modalities may also be informative. Single- and paired-pulse TMS is safe and well tolerated in children. The application of rigorous experimental designs and a combination of TMS with other research methods may increase the knowledge of pathophysiology and treatment of pediatric neurobehavioural disorders.
Eric M. Wassermann
The transcranial application of weak direct current (DC) to the brain is an effective neuromodulation technique that has had more than a century of experimental and therapeutic use. Focal DC brain polarization is now undergoing renewed interest, because of the wide acceptance of TMS as a research tool and candidate treatment for brain disorders. The effects of static electrical fields on cortical neurons in vivo have been known since the advent of intracellular recording. These effects are highly selective for neurons oriented longitudinally in the plane of the electric field. DC can enhance cognitive processes occurring in the treated area. The earliest clinical application of DC polarization was in the field of mood disorders. However, due to lack of temporal and spatial resolution, this technique does not appear particularly useful for exploring neurophysiological mechanisms.
Charles M. Epstein
This article elucidates on the concept of electromagnetism and electromagnetic induction with a view to explaining the theory of magnetic stimulation, used to cure diseases in human beings. Magnetic stimulation follows the principles of electromagnetism. A changing primary current induces secondary currents, which are called eddy currents, in the nearby conductors (human tissue in this case). The strength of the electric field is measured by its electromotive force (emf), which in turn, is measured in volts. The changing primary current also gives rise to an induced voltage in the primary loop itself. The essential circuitry of a magnetic stimulator is composed of three elements, the capacitor, inductance of the stimulation coil, and a switch to connect them. This article also explains the process of the energy flow system through the inductor-capacitor system, applying this principle to the biphasic TMS pulse.
Emergence of Higher Cognitive Functions: Reorganization of Large-Scale Brain Networks During Childhood And Adolescence
Pedro M. Paz-Alonso, Silvia A. Bunge, and Simona Ghetti
In the present chapter, we first provide an overview of neurodevelopmental changes in brain structure and function, which have implications for the development of higher cognitive functions as well as for other areas of research within developmental cognitive neuroscience. Second, we highlight neuroimaging evidence regarding the development of working memory and cognitive control processes, and the main neural mechanisms and brain networks supporting them. Third, we review behavioral and neuroimaging research on the development of memory encoding and retrieval processes, including episodic memory and mnemonic control. Finally, we summarize important current and future directions in the study of the neurocognitive mechanisms supporting the development of higher cognitive functions, noting that multidisciplinary approaches, different level of analyses, and longitudinal designs are needed to shed further light on the emergence and trajectories of these functions over development.
The Encultured Genome: Molecular Evidence for Recent Divergent Evolution in Human Neurotransmitter Genes
Chuansheng Chen, Robert K. Moyzis, Xuemei Lei, Chunhui Chen, and Qi Dong
This chapter aims to stipulate a line of research on the role of culture in recent human evolution. We discuss and evaluate several common arguments against recent human evolution. Second, we summarize empirical evidence for recent human evolution from classic examples to recent genome-wide searches. Third, using three data sets, we present detailed analyses of the extent of universal and group-specific selection of genes that are most relevant to human behaviors, namely neurotransmitter genes. We found that (1) a large number of neurotransmitter genes expressed in the central nervous system showed evidence of recent selection; (2) approximately one-fourth of these selection events appeared to be common among the four groups studied (i.e., Africans, Europeans, East Asians, and Australian Aborigines); and (3) selected gene variants were generally associated with better school-related skills but poorer performance on some cognitive and socioemotional traits, which seemed consistent with the human self-domestication hypothesis.
Zafiris J. Daskalakis and Robert Chen
Transcranial magnetic stimulation was first introduced in the late 1980s. Numerous studies have used TMS as an investigational tool to elucidate cortical physiology and to probe cognitive processes. This article introduces TMS paradigms and presents information gathered on cortical neuronal connectivity. TMS paradigms that demonstrate intracortical inhibition include short-interval cortical inhibition (SICI), cortical silence period (cSP) and long interval cortical inhibition (LICI). There are two types of cortical inhibitions from the stimulation of other brain areas, interhemispheric inhibition and cerebellum inhibition. The inhibition of the motor cortex can also be induced through the stimulation of peripheral nerves. This article talks about studies that describe interaction between inhibitory and facilitatory paradigms, the results of which are discussed in terms of cortical physiology and connectivity. The study of the interactions among cortical inhibitory and excitatory circuits may help to elucidate pathophysiology of neurological and psychiatric diseases.
V.S. Ramachandran and David Brang
Synaesthesia has been described as a perceptual experience in which a stimulus presented through one modality will spontaneously evoke a sensation experienced in an unrelated modality. While synaesthesia can occur in response to drugs, sensory deprivation, or brain damage, research has largely focused on individuals with the heritable trait, amounting to roughly 4% of the population. These experiences typically occur from increased connectivity between associated modalities, and synaesthesia is known to be involuntary, automatic, and stable over time. Furthermore, research suggests all individuals show similar cross-modal interactions to those of synaesthetes, begging the question of how different developmental synaesthesia is from acquired, drug-induced, and even sub-threshold synaesthetic associations in the normal population. This review examines the physiological basis of synaesthesia as well as the impact of learning, then works to draw parallels with synaesthesia and other similar phenomena, and closes with our current understanding of hereditary in synaesthesia and directions for future research.
How do genes affect the human brain, cognition, and culture? This chapter focuses on these interrelated areas through the lens of the serotonin transporter (5-HTT), specifically examining the behavioral regulation system in Japanese people. First, relationships between the 5-HTT gene and impulsive behavior under aversive conditions are discussed. Next, this chapter shows that in collectivistic nations, individuals with higher interdependent self-construal optimize activation of the right ventrolateral prefrontal cortex (rVLPFC) when suppressing thoughts of death. Finally, as a function of psychosocial resources, higher levels of social trust affect adaptive processes and increase rVLPFC activity, all of which are geared toward modulating social pain. Thus, S allele carriers are more likely to adapt to collectivistic cultures because of the functional properties of the S allele, which may in turn promote collectivistic cultural norms.
Julian E. Asher and Duncan A. Carmichael
Synaesthesia is a neurodevelopmental condition characterised by anomalous sensory perceptions and associated alterations in cognitive function. This chapter summarises what is known about the familial transmission of synaesthesia and its genetic underpinnings. Early familiality studies showed evidence for a strong genetic predisposition, a highly skewed female: male ratio, and an absence of male-to-male transmission. These patterns supported an early hypothesis of a single-gene X-linked dominant mode of inheritance with male lethality. Subsequent analyses in larger samples indicated that the mode of inheritance was likely to be more complex, with both the strong female skew and absence of male-to-male transmission brought into question. We review in detail the first whole genome linkage scan for auditory-visual synaesthesia (Asher et al. 2009) and a subsequent family linkage study on coloured sequence synaesthesia (Tomson et al. 2011). Together these results suggest linkage to five chromosomes (2, 5, 6, 12 and 16) but give no support for linkage to the X-chromosome. We discuss candidate genes within these regions and potential implications for the aetiology of synaesthesia. We also discuss the implications of these pioneering genome scans for our understanding of synaesthesia and of how different synaesthetic phenotypes may arise from different genetic predispositions interacting with other genes and with the environment.
Simone Rossi, Stefano F. Cappa, and Paolo Maria Rossini
Transcranial magnetic stimulation (TMS) is a sophisticated approach for interfering with human memory and reasoning due to its ability to transiently interfere with the functions of the specialized cortical network, especially when applied as repetitive (r)TMS. This article reviews TMS studies dealing with short-term retention, working memory, and with the episodic component of declarative memory. It also considers certain aspects of semantic memory and nonverbal reasoning. Furthermore, it discusses methodological considerations about the experimental designs, which can be used for the investigation of human cognitive functions. This article emphasizes the fact that higher cognitive functions provide an example as to how underlying physiological mechanisms cannot be fully disclosed by investigations based on a single technique. Studies to develop a true multimodal approach are being undertaken. In this light, behavioural interference studies will gain new power in combination with disruptive and correlational methodologies, establishing causality in a more sophisticated manner.
Jacinta OʼShea and Matthew F. S. Rushworth
This article reviews the contribution of transcranial magnetic stimulation (TMS) research to the understanding of attention, eye movements, visual search, and neglect. It considers how TMS studies have confirmed, refined, or challenged prevailing ideas about the neural basis of higher visual cognition. It shows that TMS has enhanced the understanding of the location, timing, and functional roles of visual cognitive processes in the human brain. The main focus is on studies of posterior parietal cortex (PPC), with reference to recent work on the frontal eye fields (FEFs). TMS offers many advantages to complement neuropsychological patient studies to enhance the understanding of how the fronto-parietal cortical nerves function. The visuo-spatial neglect- and extinction-like deficits incurred by parietal damage have been modelled successfully using TMS. Future work might be directed at teasing apart the distinct functional roles of nodes within this frontoparietal network in different sensorimotor contexts.
Identifying a Cultural Resource: Neural Mechanisms Underlying Familial Influence on Adolescent Risk Taking
Eva H. Telzer, Andrew J. Fuligni, and Adriana Galvan
Family obligation, which implies children’s role in the support and assistance of their family, is a fundamental aspect of family life. Family obligation has important implications for the adjustment of adolescents from Mexican backgrounds, relating to lower levels of risky behavior. Risk taking underlies many behavioral and health factors, such as substance use and externalizing behavior, that contribute to the public health burden during the adolescent period. Advances in developmental neuroscience have identified key neurobiological underpinnings of adolescent risk taking, but there is little understanding of how these neural processes interact with cultural and social processes to promote or prevent risk taking. We present a multimethod, longitudinal program of research that uses self-reports of risk taking and substance use, experimental tasks, and functional magnetic resonance imaging to examine the mechanisms by which a culturally meaningful type of family relationship—family obligation—buffers Mexican youth from drug use and risk taking.