Magnetic stimulation studies of visual cognition

The panoply of non-invasive techniques for brain imaging is responsible for much of the current excitement in cognitive neuroscience; sensory, perceptual and cognitive behaviour can now be correlated with cerebral blood flow as assessed by functional imaging, the electrical fields generated by populations of neurons or changes in magnetic fields created by electrical activity. Correlations between localized brain activity and behaviour, however, do not of themselves establish that any brain area is necessary for a particular task; necessity is the domain of the lesion technique. Transcranial magnetic stimulation (TMS) is a technique that can be used non-invasively to produce reversible functional disruption and has already been used to investigate visual detection, discrimination, attention and plasticity. The power of TMS as a `lesion' technique lies in the opportunity to combine reversible disruption with high degrees of spatial and temporal resolution. In this review we trace some of the major developments in the use of TMS as a technique for the investigation of visual cognition.     

Introducing Transcranial Magnetic Stimulation (TMS) and its Property of Causal Inference in Investigating Brain-Function Relationships

Transcranial magnetic stimulation (TMS) is a method capable of transiently modulating neural excitability. Depending on the stimulation parameters information processing in the brain can be either enhanced or disrupted. This way the contribution of different brain areas involved in mental processes can be studied, allowing a functional decomposition of cognitive behavior both in the temporal and spatial domain, hence providing a functional resolution of brain/mind processes. The aim of the present paper is to argue that TMS with its ability to draw causal inferences on function and its neural representations is a valuable neurophysiological tool for investigating the causal basis of neuronal functions and can provide substantive insight into the modern interdisciplinary and (anti)reductionist neurophilosophical debates concerning the relationships between brain functions and mental abilities. Thus, TMS can serve as a heuristic method for resolving causal issues in an arena where only correlative tools have traditionally been available.     

State-dependency in brain stimulation studies of perception and cognition

We address the importance of understanding initial states of neuronal populations and of state-dependent responses in cognitive neuroscience experiments with special emphasis on brain stimulation studies of perception and cognition. The approach we present is based on evidence that behavioural and perceptual effects of transcranial magnetic stimulation (TMS) are determined by initial neural activation state; by systematically manipulating neural activation states before application of TMS, one can selectively target specific, even spatially overlapping neural populations within the affected region. This approach is potentially of great benefit to cognitive neuroscience and remediation programmes as it combines high spatial and functional resolution with the ability to assess causality.     

Mechanisms and the current state of transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is unique among the current brain stimulation techniques because it is relatively non-invasive. TMS markedly differs from vagus nerve stimulation, deep brain stimulation and magnetic seizure therapy, all of which require either an implanted prosthesis or general anesthesia, or both. Since its rebirth in its modern form in 1985, TMS has already shown potential usefulness in at least three important domains-as a basic neuroscience research instrument, as a potential clinical diagnostic tool, and as a therapy for several different neuropsychiatric conditions. The TMS scientific literature has now expanded beyond what a single summary article can adequately cover. This review highlights several new developments in combining TMS with functional brain imaging, using TMS as a psychiatric therapy, potentially using TMS to enhance performance, and finally recent advances in the core technology of TMS. TMS' ability to non-invasively and focally stimulate the brain of an awake human is proving to be a most important development for neuroscience in general, and neuropsychiatry in particular.     

Retooling Techno-Moral Scenarios. A Revisited Technique for Exploring Alternative Regimes of Responsibility for Human Enhancement

The techno-moral scenarios (TMS) approach has been developed to explore the interplay between technology, society and morality. Focused on new and emerging sciences and technologies, techno-moral scenarios can be used to inform and enhance public deliberation on the desirability of socio-technical trajectories. The article presents an attempt to hybridise this scenario tool, complementing the focus on ethics with an explicit acknowledgement of the multiple meanings of responsibility and of the plurality of its regimes, i.e. the institutional arrangements presiding over the assumption and assignment of responsibilities. We call this integrated technique ‘rTMS’ to stress the continuity with the original technique and, at the same time, to highlight the additional element we aim to develop: responsibility. The article describes this approach and illustrates a loosely standardised procedure that can be used to organise and conduct public engagement workshops based on rTMS.     

Group cognition,membership change,and performance: Investigating the benefits and detriments of collective knowledge

This study analyzes the effects of group membership change on group cognition and performance to determine how groups can simultaneously leverage oldtimers’ collective knowledge and a newcomer’s expertise. Our analysis focuses specifically on the interrelated effects of the two components of a transactive memory system (TMS)—TMS structure and TMS processes—to explain the cognitive mechanisms through which membership change affects group performance. Results from a laboratory study show that groups that experience partial membership change tend to rely on the TMS structure that oldtimers developed in their original group, and that doing so is ultimately detrimental to performance because it creates inefficient TMS processes. Results from a supplemental study indicate that these TMS process inefficiencies can be avoided when oldtimers are instructed to reflect upon their collective knowledge prior to task execution. We discuss the implications for managing group cognition in organizations where membership change is prevalent.     

TMS effects on subjective and objective measures of vision: stimulation intensity and pre- versus post-stimulus masking

Transcranial magnetic stimulation (TMS) can be used to mask visual stimuli, disrupting visual task performance or preventing visual awareness. While TMS masking studies generally fix stimulation intensity, we hypothesized that varying the intensity of TMS pulses in a masking paradigm might inform several ongoing debates concerning TMS disruption of vision as measured subjectively versus objectively, and pre-stimulus (forward) versus post-stimulus (backward) TMS masking. We here show that both pre-stimulus TMS pulses and post-stimulus TMS pulses could strongly mask visual stimuli. We found no dissociations between TMS effects on the subjective and objective measures of vision for any masking window or intensity, ruling out the option that TMS intensity levels determine whether dissociations between subjective and objective vision are obtained. For the post-stimulus time window particularly, we suggest that these data provide new constraints for (e.g. recurrent) models of vision and visual awareness. Finally, our data are in line with the idea that pre-stimulus masking operates differently from conventional post-stimulus masking.     

Enhancing picture naming with transcranial magnetic stimulation

The enhancement of cognitive function in healthy subjects by medication, training or intervention yields increasing political, social and ethical attention. In this paper facilitatory effects of single-pulse TMS and repetitive TMS on a simple picture naming task are presented. A significant shortening of picture naming latencies was observed after single-pulse TMS over Wernicke's area. The accuracy of the response was not affected by this speed effect. After TMS over the dominant motor cortex or over the non-dominant temporal lobe, however, no facilitation of picture naming was observed. In the rTMS experiments only rTMS of Wernicke's area had an impact on picture naming latencies resulting in a shortening of naming latencies without affecting the accuracy of the response. rTMS over the visual cortex, Broca's area or over the corresponding sites in the non-dominant hemisphere had no effect. Single-pulse TMS is able to facilitate lexical processes due to a general preactivation of language-related neuronal networks when delivered over Wernicke's area. Repetitive transcranial magnetic stimulation over Wernicke's area also leads to a brief facilitation of picture naming possibly by shortening linguistic processing time. Whether TMS or rTMS can be used to aid linguistic therapy in the rehabilitation phase of aphasic patients should be subject of further investigations.     

The role of the human extrastriate visual cortex in mirror symmetry discrimination: a TMS-adaptation study

The human visual system is able to efficiently extract symmetry information from the visual environment. Prior neuroimaging evidence has revealed symmetry-preferring neuronal representations in the dorsolateral extrastriate visual cortex; the objective of the present study was to investigate the necessity of these representations in symmetry discrimination. This was accomplished by the use of state-dependent transcranial magnetic stimulation, which combines the fine resolution of adaptation paradigms with the assessment of causality. Subjects were presented with adapters and targets consisting of dot configurations that could be symmetric along either the vertical or horizontal axis (or they could be non-symmetric), and they were asked to perform a symmetry discrimination task on the targets while fixating the center of the screen. TMS was applied during the delay between the adapter and the test stimulus over one of four different sites: Left or Right V1/V2, or left or right dorsolateral extrastriate cortex (DLO). TMS over both Left and Right DLO reduced the adaptation effect in detecting vertical and horizontal symmetry, although the Left DLO effect on horizontal symmetry and the Right DLO effect on both vertical and horizontal symmetry were present only when considering subjects who showed a behavioral adaptation effect in the baseline No-TMS condition. Application of TMS over the Left or Right V1/V2 did not modulate the adaptation effect. Overall, these data suggest that both the Left and Right DLO contain neuronal representations tuned to mirror symmetry which play a causal role in symmetry discrimination.     

Neurophysiology and neuroanatomy of reflexive and volitional saccades as revealed by lesion studies with neurological patients and transcranial magnetic stimulation (TMS)

This review discusses the neurophysiology and neuroanatomy of the cortical control of reflexive and volitional saccades in humans. The main focus is on classical lesion studies and studies using the interference method of transcranial magnetic stimulation (TMS). To understand the behavioural function of a region, it is essential to assess oculomotor deficits after a focal lesion using a variety of oculomotor paradigms, and to study the oculomotor consequences of the lesion in the chronic phase. Saccades are controlled by different cortical regions, which could be partially specialised in the triggering of a specific type of saccade. The division of saccades into reflexive visually guided saccades and intentional or volitional saccades corresponds to distinct regions of the neuronal network, which are involved in the control of such saccades.TMS allows to specifically interfere with the functioning of a region within an intact oculomotor network. TMS provides advantages in terms of temporal resolution, allowing to interfere with brain functioning in the order of milliseconds, thereby allowing to define the time course of saccade planning and execution.In the first part of the paper, we present an overview of the cortical structures important for saccade control, and discuss the pro’s and con’s of the different methodological approaches to study the cortical oculomotor network. In the second part, the functional network involved in reflexive and volitional saccades is presented. Finally, studies concerning recovery mechanisms after a lesion of the oculomotor cortex are discussed.     

Neurophysiology and neuroanatomy of reflexive and volitional saccades as revealed by lesion studies with neurological patients and transcranial magnetic stimulation (TMS)

This review discusses the neurophysiology and neuroanatomy of the cortical control of reflexive and volitional saccades in humans. The main focus is on classical lesion studies and studies using the interference method of transcranial magnetic stimulation (TMS). To understand the behavioural function of a region, it is essential to assess oculomotor deficits after a focal lesion using a variety of oculomotor paradigms, and to study the oculomotor consequences of the lesion in the chronic phase. Saccades are controlled by different cortical regions, which could be partially specialised in the triggering of a specific type of saccade. The division of saccades into reflexive visually guided saccades and intentional or volitional saccades corresponds to distinct regions of the neuronal network, which are involved in the control of such saccades.TMS allows to specifically interfere with the functioning of a region within an intact oculomotor network. TMS provides advantages in terms of temporal resolution, allowing to interfere with brain functioning in the order of milliseconds, thereby allowing to define the time course of saccade planning and execution.In the first part of the paper, we present an overview of the cortical structures important for saccade control, and discuss the pro’s and con’s of the different methodological approaches to study the cortical oculomotor network. In the second part, the functional network involved in reflexive and volitional saccades is presented. Finally, studies concerning recovery mechanisms after a lesion of the oculomotor cortex are discussed.     

虚拟团队中交互记忆系统理论研究现状述评

交互记忆系统(Transactive Memory System,TMS),团队成员在交流的过程中形成的一种合作性分工系统,简单来说就是团队成员对于“谁知道什么”的一种共同认知.通过TMS,团队成员能够协调彼此的专长从而提高团队知识整合和共享水平.文章回顾了TMS和虚拟团队的相关概念,重点从虚拟团队中TMS的形成、效用以及虚拟性与TMS的关系三个角度对虚拟团队中TMS的相关研究进行了归纳,最后指出未来不仅需要深入研究团队输入、输出和调节因素的影响,还需考虑到不同的信息技术的影响以及研究方法和范围的完善.     

背外侧前额叶对主动遗忘负性社会反馈的作用：针对抑郁症的TMS研究

抑郁症患者的负性心境可能源于其抑制功能障碍。患者在主动遗忘负性材料时无法有效调用背外侧前额叶(the dorsolateral prefrontal cortex, DLPFC)等负责抑制控制的额叶脑网络。同时, 患者对社会信息的加工比对非社会信息的加工存在更明显的认知神经障碍, 很难主动遗忘对自己不利的社会反馈信息。为了提高抑郁症患者对负性社会反馈的主动遗忘能力, 本研究采用经颅磁刺激技术(transcranial magnetic stimulation, TMS), 考察抑郁症患者在左侧(n = 32)或右侧DLPFC (n = 30)被激活后其记忆控制能力的改变。结果表明, 当患者的DLPFC被TMS激活时, 他们对社会拒绝的回忆正确率与健康对照组(n = 31)无差异, 且TMS激活右侧DLPFC还改善了患者对他人的社会态度。本研究是采用TMS提高抑郁症患者主动遗忘能力的首次尝试, 研究结果不但支持了DLPFC与记忆控制功能的因果关系, 还为临床治疗抑郁症、创伤后应激障碍、药物成瘾等患者的记忆控制缺陷提供了明确的神经靶点。     

Neuromodulation as a cognitive enhancement strategy in healthy older adults: promises and pitfalls

Increases in life expectancy have been followed by an upsurge of age-associated cognitive decline. Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) have risen as promising approaches to prevent or delay such cognitive decline. However, consensus has not yet been reached about their efficacy in improving cognitive functioning in healthy older adults. Here we review the effects of TMS and tDCS on cognitive abilities in healthy older adults. Despite considerable variability in the targeted cognitive domains, design features and outcomes, the results generally show an enhancement or uniform benefit across studies. Most studies employed tDCS, suggesting that this technique is particularly well-suited for cognitive enhancement. Further work is required to determine the viability of these techniques as tools for long-term cognitive improvement. Importantly, the combination of TMS/tDCS with other cognitive enhancement strategies may be a promising strategy to alleviate the cognitive decline associated with the healthy aging process.     

Transcranial magnetic stimulation as a tool for cognitive studies

Transcranial Magnetic Stimulation (TMS) is a tool for the non-invasive stimulation of the human brain. It allows the activation of arbitrary sites of the superficial cortex and, combined with other brain-imaging techniques such as EEG, PET, and fMRI, it can be used to evaluate cortical excitability and connectivity. This is of major importance in, for example, the study of cognitive processes such as language, learning, memory and self-representation, which are thought to be represented in multiple brain areas. The mechanisms of action of TMS are known on a basic level, but its effect on the activation state of brain tissue is still poorly understood. Clinical applications of TMS have also been proposed and guidelines for its safe use drafted.     

Occipital long-interval paired pulse TMS leads to slow wave components in NREM sleep

Neural correlates of conscious vs unconscious states can be studied by contrasting EEG markers of brain activity between those two states. Here, a task-free experimental setup was used to study the state dependent effects of occipital transcranial magnetic stimulation (TMS). EEG responses to single and paired pulse TMS with an inter-stimulus-interval (ISI) of 100 ms were investigated under Non-REM (NREM) sleep and wakefulness. In the paired pulse TMS condition adopting this long ISI, a robust positive deflection starting around 200 ms after the second pulse was found. This component was not obtained under wakefulness or when a single TMS pulse was applied in sleep. These findings are discussed in the context of NREM sleep slow waves. The present results indicate that the long interval paired-pulse paradigm could be used to manipulate plasticity processes in the visual cortex. The present setup might also become useful for evaluating states of consciousness.     

Transcranial magnetic stimulation in child psychiatry: disturbed motor system excitability in hypermotoric syndromes

Normal development and dysfunctions of motor system excitability can be investigated in vivo by means of single‐ and paired‐pulse transcranial magnetic stimulation (TMS). While different TMS‐parameters show different developmental time courses between 8 and 16 years of age, distinct dysfunctional patterns of motor system excitability can be demonstrated in child psychiatric disorders with hypermotoric behavior: in tic disorder, a shortened cortical silent period can be stated providing evidence for deficient inhibitory mechanisms within the sensorimotor loop, probably primarily at the level of the basal ganglia. In attention deficit hyperactivity disorder (ADHD), a decreased intracortical inhibition indicates deficient inhibitory mechanisms within the motor cortex (but enhancement of intracortical inhibition after oral intake of 10 mg methylphenidate). In children with comorbid ADHD and tic disorder, the findings of a reduced intracortical inhibition as well as a shortened cortical silent period provide evidence for additive effects at the level of motor system excitability. Thus, TMS allows us to obtain substantial insight into both the normal development and the neurobiological basis of hypermotoric syndromes in child psychiatry.