Modulating neuronal activity produces specific and long-lasting changes in numerical competence

How does enhancing cognition affect human values? How does this translate into social responsibility?

The past decade has seen a rise in the use of different technologies aimed at enhancing cognition of normal healthy individuals. While values have been acknowledged to be an important aspect of cognitive enhancement practices, the discussion has predominantly focused on just a few values, such as safety, peer pressure, and authenticity. How are values, in a broader sense, affected by enhancing cognitive abilities? Is this dependent on the type of technology or intervention used to attain the enhancement, or does the cognitive domain targeted play a bigger role in how values are affected? Values are not only likely to be affected by cognitive enhancement practices; they also play a crucial role in defining the type of interventions that are likely to be undertaken. This paper explores the way values affect and are affected by enhancing cognitive abilities. Furthermore, it argues that knowledge of the interplay between values and cognitive enhancement makes a strong case for social responsibility around cognitive enhancement practices.

[From brain imaging to good teaching? implicating from neuroscience for research on learning and instruction]

Psychiatric disorders in childhood and adolescence, in particular attention deficit disorder or specific learning disorders like developmental dyslexia and developmental dyscalculia, affect academic performance and learning at school. Recent advances in neuroscientific research have incited an intensive debate both in the general public and in the field of educational and instructional science as well as to whether and to what extent these new findings in the field of neuroscience might be of importance for school-related learning and instruction. In this review, we first summarize neuroscientific findings related to the development of attention, working memory and executive functions in typically developing children and then evaluate their relevance for school-related learning. We present an overview of neuroimaging studies of specific learning disabilities such as developmental dyslexia and developmental dyscalculia, and critically discuss their practical implications for educational and teaching practice, teacher training, early diagnosis as well as prevention and disorder-specific therapy. We conclude that the new interdisciplinary field of neuroeducation cannot be expected to provide direct innovative educational applications (e.g., teaching methods). Rather, the future potential of neuroscience lies in creating a deeper understanding of the underlying cognitive mechanisms and pathomechanisms of learning processes and learning disorders.

Enhancement and Civic Virtue

Opponents of biomedical enhancement frequently adopt what Allen Buchanan has called the Personal Goods Assumption. On this assumption, the benefits of biomedical enhancement will accrue primarily to those individuals who undergo enhancements, not to wider society. Buchanan has argued that biomedical enhancements might in fact have substantial social benefits by increasing productivity. We outline another way in which enhancements might benefit wider society: by augmenting civic virtue and thus improving the functioning of our political communities. We thus directly confront critics of biomedical enhancement who argue that it will lead to a loss of social cohesion and a breakdown in political life.

Transcranial direct current stimulation and simultaneous functional magnetic resonance imaging

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that uses weak electrical currents administered to the scalp to manipulate cortical excitability and, consequently, behavior and brain function. In the last decade, numerous studies have addressed short-term and long-term effects of tDCS on different measures of behavioral performance during motor and cognitive tasks, both in healthy individuals and in a number of different patient populations. So far, however, little is known about the neural underpinnings of tDCS-action in humans with regard to large-scale brain networks. This issue can be addressed by combining tDCS with functional brain imaging techniques like functional magnetic resonance imaging (fMRI) or electroencephalography (EEG). In particular, fMRI is the most widely used brain imaging technique to investigate the neural mechanisms underlying cognition and motor functions. Application of tDCS during fMRI allows analysis of the neural mechanisms underlying behavioral tDCS effects with high spatial resolution across the entire brain. Recent studies using this technique identified stimulation induced changes in task-related functional brain activity at the stimulation site and also in more distant brain regions, which were associated with behavioral improvement. In addition, tDCS administered during resting-state fMRI allowed identification of widespread changes in whole brain functional connectivity. Future studies using this combined protocol should yield new insights into the mechanisms of tDCS action in health and disease and new options for more targeted application of tDCS in research and clinical settings. The present manuscript describes this novel technique in a step-by-step fashion, with a focus on technical aspects of tDCS administered during fMRI.

Not all brains are created equal: the relevance of individual differences in responsiveness to transcranial electrical stimulation

A current issue in the research of augmentation of brain functions using transcranial electrical stimulation (tES) is the diversity and inconsistency in outcome results. Similar studies often report different results, depending on the parameters and tasks used. Such inconsistencies have led to significant doubts about the efficacy of the method in the broader scientific community, despite its promising potential for patient recovery and treatment. Evidence on the large variability in individual cortical excitability and response to tES suggests that stimulation may affect individuals differently, depending on the subject’s age, gender, brain state, hormonal levels, and pre-existing regional excitability. Certain factors might even lead to the reversal of polarity-dependent effects, and therefore have crucial implications for neurorehabilitation and cognitive enhancement. Research paradigms may have to be refined in the future to avoid the confounding effects of such factors.

Preliminary evidence for performance enhancement following parietal lobe stimulation in Developmental Dyscalculia

Nearly 7% of the population exhibit difficulties in dealing with numbers and performing arithmetic, a condition named Developmental Dyscalculia (DD), which significantly affects the educational and professional outcomes of these individuals, as it often persists into adulthood. Research has mainly focused on behavioral rehabilitation, while little is known about performance changes and neuroplasticity induced by the concurrent application of brain-behavioral approaches. It has been shown that numerical proficiency can be enhanced by applying a small-yet constant-current through the brain, a non-invasive technique named transcranial electrical stimulation (tES). Here we combined a numerical learning paradigm with transcranial direct current stimulation (tDCS) in two adults with DD to assess the potential benefits of this methodology to remediate their numerical difficulties. Subjects learned to associate artificial symbols to numerical quantities within the context of a trial and error paradigm, while tDCS was applied to the posterior parietal cortex (PPC). The first subject (DD1) received anodal stimulation to the right PPC and cathodal stimulation to the left PPC, which has been associated with numerical performance's improvements in healthy subjects. The second subject (DD2) received anodal stimulation to the left PPC and cathodal stimulation to the right PPC, which has been shown to impair numerical performance in healthy subjects. We examined two indices of numerical proficiency: (i) automaticity of number processing; and (ii) mapping of numbers onto space. Our results are opposite to previous findings with non-dyscalculic subjects. Only anodal stimulation to the left PPC improved both indices of numerical proficiency. These initial results represent an important step to inform the rehabilitation of developmental learning disabilities, and have relevant applications for basic and applied research in cognitive neuroscience, rehabilitation, and education.

Strengthening connections: functional connectivity and brain plasticity

The ascendancy of functional neuroimaging has facilitated the addition of network-based approaches to the neuropsychologist's toolbox for evaluating the sequelae of brain insult. In particular, intrinsic functional connectivity (iFC) mapping of resting state fMRI (R-fMRI) data constitutes an ideal approach to measuring macro-scale networks in the human brain. Beyond the value of iFC mapping for charting how the functional topography of the brain is altered by insult and injury, iFC analyses can provide insights into experience-dependent plasticity at the macro level of large-scale functional networks. Such insights are foundational to the design of training and remediation interventions that will best facilitate recovery of function. In this review, we consider what is currently known about the origin and function of iFC in the brain, and how this knowledge is informative in neuropsychological settings. We then summarize studies that have examined experience-driven plasticity of iFC in healthy control participants, and frame these findings in terms of a schema that may aid in the interpretation of results and the generation of hypotheses for rehabilitative studies. Finally, we outline some caveats to the R-fMRI approach, as well as some current developments that are likely to bolster the utility of the iFC paradigm for neuropsychology.

When is diminishment a form of enhancement? Rethinking the enhancement debate in biomedical ethics

The enhancement debate in neuroscience and biomedical ethics tends to focus on the augmentation of certain capacities or functions: memory, learning, attention, and the like. Typically, the point of contention is whether these augmentative enhancements should be considered permissible for individuals with no particular “medical” disadvantage along any of the dimensions of interest. Less frequently addressed in the literature, however, is the fact that sometimes the diminishment of a capacity or function, under the right set of circumstances, could plausibly contribute to an individual's overall well-being: more is not always better, and sometimes less is more. Such cases may be especially likely, we suggest, when trade-offs in our modern environment have shifted since the environment of evolutionary adaptation. In this article, we introduce the notion of “diminishment as enhancement” and go on to defend a welfarist conception of enhancement. We show how this conception resolves a number of definitional ambiguities in the enhancement literature, and we suggest that it can provide a useful framework for thinking about the use of emerging neurotechnologies to promote human flourishing.

Long-Term Abacus Training Induces Automatic Processing of Abacus Numbers in Children

Abacus-based mental calculation (AMC) is a unique strategy for arithmetic that is based on the mental abacus. AMC experts can solve calculation problems with extraordinarily fast speed and high accuracy. Previous studies have demonstrated that abacus experts showed superior performance and special neural correlates during numerical tasks. However, most of those studies focused on the perception and cognition of Arabic numbers. It remains unclear how the abacus numbers were perceived. By applying a similar enumeration Stroop task, in which participants are presented with a visual display containing two abacus numbers and asked to compare the numerosity of beads that consisted of the abacus number, in the present study we investigated the automatic processing of the numerical value of abacus numbers in abacus-trained children. The results demonstrated a significant congruity effect in the numerosity comparison task for abacus-trained children, in both reaction time and error rate analysis. These results suggested that the numerical value of abacus numbers was perceived automatically by the abacus-trained children after long-term training.

Transcranial direct current stimulation of the dorsolateral prefrontal cortex modulates repetition suppression to unfamiliar faces: an ERP study

Repeated visual processing of an unfamiliar face suppresses neural activity in face-specific areas of the occipito-temporal cortex. This "repetition suppression" (RS) is a primitive mechanism involved in learning of unfamiliar faces, which can be detected through amplitude reduction of the N170 event-related potential (ERP). The dorsolateral prefrontal cortex (DLPFC) exerts top-down influence on early visual processing. However, its contribution to N170 RS and learning of unfamiliar faces remains unclear. Transcranial direct current stimulation (tDCS) transiently increases or decreases cortical excitability, as a function of polarity. We hypothesized that DLPFC excitability modulation by tDCS would cause polarity-dependent modulations of N170 RS during encoding of unfamiliar faces. tDCS-induced N170 RS enhancement would improve long-term recognition reaction time (RT) and/or accuracy rates, whereas N170 RS impairment would compromise recognition ability. Participants underwent three tDCS conditions in random order at ∼72 hour intervals: right anodal/left cathodal, right cathodal/left anodal and sham. Immediately following tDCS conditions, an EEG was recorded during encoding of unfamiliar faces for assessment of P100 and N170 visual ERPs. The P3a component was analyzed to detect prefrontal function modulation. Recognition tasks were administered ∼72 hours following encoding. Results indicate the right anodal/left cathodal condition facilitated N170 RS and induced larger P3a amplitudes, leading to faster recognition RT. Conversely, the right cathodal/left anodal condition caused N170 amplitude and RTs to increase, and a delay in P3a latency. These data demonstrate that DLPFC excitability modulation can influence early visual encoding of unfamiliar faces, highlighting the importance of DLPFC in basic learning mechanisms.

Cognitive enhancement

Cognitive enhancement refers to the improvement of cognitive ability in normal healthy individuals. In this article, we focus on the use of pharmaceutical agents and brain stimulation for cognitive enhancement, reviewing the most common methods of pharmacologic and electronic cognitive enhancement, and the mechanisms by which they are believed to work, the effectiveness of these methods and their prevalence. We note the many gaps in our knowledge of these matters, including open questions about the size, reliability and nature of the enhancing effects, and we conclude with recommendations for further research. WIREs Cogn Sci 2014, 5:95-103. doi: 10.1002/wcs.1250 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Does excitatory fronto-extracerebral tDCS lead to improved working memory performance?

Evidence suggests that excitatory transcranial direct current stimulation (tDCS) may improve performance on a wide variety of cognitive tasks. Due to the non-invasive and inexpensive nature of the method, harnessing its potential could be particularly useful for the treatment of neuropsychiatric illnesses involving cognitive dysfunction. However, questions remain regarding the efficacious stimulation parameters. Here, using a double-blind between-subjects design, we explored whether 1 mA excitatory (anodal) left dorsolateral prefrontal cortex stimulation with a contralateral extracerebral reference electrode, leads to enhanced working memory performance across two days, relative to sham stimulation. Participants performed the 3-back, a test of working memory, at baseline, and during and immediately following stimulation on two days, separated by 24-48 hours. Active stimulation did not significantly enhance performance versus sham over the course of the experiment. However, exploratory comparisons did reveal a significant effect of stimulation group on performance during the first stimulation phase only, with active stimulation recipients performing better than sham. While these results do not support the hypothesis that dorsolateral prefrontal cortex tDCS boosts working memory, they raise the possibility that its effects may be greatest during early learning stages.

The link between mental rotation ability and basic numerical representations

Mental rotation and number representation have both been studied widely, but although mental rotation has been linked to higher-level mathematical skills, to date it has not been shown whether mental rotation ability is linked to the most basic mental representation and processing of numbers. To investigate the possible connection between mental rotation abilities and numerical representation, 43 participants completed four tasks: 1) a standard pen-and-paper mental rotation task; 2) a multi-digit number magnitude comparison task assessing the compatibility effect, which indicates separate processing of decade and unit digits; 3) a number-line mapping task, which measures precision of number magnitude representation; and 4) a random number generation task, which yields measures both of executive control and of spatial number representations. Results show that mental rotation ability correlated significantly with both size of the compatibility effect and with number mapping accuracy, but not with any measures from the random number generation task. Together, these results suggest that higher mental rotation abilities are linked to more developed number representation, and also provide further evidence for the connection between spatial and numerical abilities.

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We show a link between mental rotation ability (MRA) and numerical representation.

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MRA correlated with a measure of holding concurrent multiple number representations.

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MRA correlated with a measure of number representation precision (number line task).

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MRA did not correlate with an executive control task (random number generation).

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These findings strengthen the link observed between spatial and numerical abilities.

Bilateral bi-cephalic tDCS with two active electrodes of the same polarity modulates bilateral cognitive processes differentially [corrected]

Transcranial direct current stimulation (tDCS) is an innovative method to explore the causal structure-function relationship of brain areas. We investigated the specificity of bilateral bi-cephalic tDCS with two active electrodes of the same polarity (e.g., cathodal on both hemispheres) applied to intraparietal cortices bilaterally using a combined between- and within-task approach. Regarding between-task specificity, we observed that bilateral bi-cephalic tDCS affected a numerical (mental addition) but not a control task (colour word Stroop), indicating a specific influence of tDCS on numerical but not on domain general cognitive processes associated with the bilateral IPS. In particular, the numerical effect of distractor distance was more pronounced under cathodal than under anodal stimulation. Moreover, with respect to within-task specificity we only found the numerical distractor distance effect in mental addition to be modulated by direct current stimulation, whereas the effect of target identity was not affected. This implies a differential influence of bilateral bi-cephalic tDCS on the recruitment of different processing components within the same task (number magnitude processing vs. recognition of familiarity). In sum, this first successful application of bilateral bi-cephalic tDCS with two active electrodes of the same polarity in numerical cognition research corroborates the specific proposition of the Triple Code Model that number magnitude information is represented bilaterally in the intraparietal cortices.

Left cathodal trans-cranial direct current stimulation of the parietal cortex leads to an asymmetrical modulation of the vestibular-ocular reflex

Multi-sensory visuo-vestibular cortical areas within the parietal lobe are important for spatial orientation and possibly for descending modulation of the vestibular-ocular reflex (VOR). Functional imaging and lesion studies suggest that vestibular cortical processing is localized primarily in the non-dominant parietal lobe. However, the role of inter-hemispheric parietal balance in vestibular processing is poorly understood. Therefore, we tested whether experimentally induced asymmetries in right versus left parietal excitability would modulate vestibular function. VOR function was assessed in right-handed normal subjects during caloric ear irrigation (30 °C), before and after trans-cranial direct current stimulation (tDCS) was applied bilaterally over the parietal cortex. Bilateral tDCS with the anode over the right and the cathode over the left parietal region resulted in significant asymmetrical modulation of the VOR, with highly suppressed responses during the right caloric irrigation (i.e. rightward slow phase nystagmus). In contrast, we observed no VOR modulation during either cathodal stimulation of the right parietal cortex or SHAM tDCS conditions. Application of unilateral tDCS revealed that the left cathodal stimulation was critical in inducing the observed modulation of the VOR. We show that disruption of parietal inter-hemispheric balance can induce asymmetries in vestibular function. This is the first report using neuromodulation to show right hemisphere dominance for vestibular cortical processing.

Noninvasive brain stimulation: from physiology to network dynamics and back

Noninvasive brain stimulation techniques have been widely used for studying the physiology of the CNS, identifying the functional role of specific brain structures and, more recently, exploring large-scale network dynamics. Here we review key findings that contribute to our understanding of the mechanisms underlying the physiological and behavioral effects of these techniques. We highlight recent innovations using noninvasive stimulation to investigate global brain network dynamics and organization. New combinations of these techniques, in conjunction with neuroimaging, will further advance the utility of their application.

Enhancing performance in numerical magnitude processing and mental arithmetic using transcranial Direct Current Stimulation (tDCS)

The ability to accurately process numerical magnitudes and solve mental arithmetic is of highest importance for schooling and professional career. Although impairments in these domains in disorders such as developmental dyscalculia (DD) are highly detrimental, remediation is still sparse. In recent years, transcranial brain stimulation methods such as transcranial Direct Current Stimulation (tDCS) have been suggested as a treatment for various neurologic and neuropsychiatric disorders. The posterior parietal cortex (PPC) is known to be crucially involved in numerical magnitude processing and mental arithmetic. In this study, we evaluated whether tDCS has a beneficial effect on numerical magnitude processing and mental arithmetic. Due to the unclear lateralization, we stimulated the left, right as well as both hemispheres simultaneously in two experiments. We found that left anodal tDCS significantly enhanced performance in a number comparison and a subtraction task, while bilateral and right anodal tDCS did not induce any improvements compared to sham. Our findings demonstrate that the left PPC is causally involved in numerical magnitude processing and mental arithmetic. Furthermore, we show that these cognitive functions can be enhanced by means of tDCS. These findings encourage to further investigate the beneficial effect of tDCS in the domain of mathematics in healthy and impaired humans.

Ethics of the electrified mind: defining issues and perspectives on the principled use of brain stimulation in medical research and clinical care

In recent years, non-pharmacologic approaches to modifying human neural activity have gained increasing attention. One of these approaches is brain stimulation, which involves either the direct application of electrical current to structures in the nervous system or the indirect application of current by means of electromagnetic induction. Interventions that manipulate the brain have generally been regarded as having both the potential to alleviate devastating brain-related conditions and the capacity to create unforeseen and unwanted consequences. Hence, although brain stimulation techniques offer considerable benefits to society, they also raise a number of ethical concerns. In this paper we will address various dilemmas related to brain stimulation in the context of clinical practice and biomedical research. We will survey current work involving deep brain stimulation, transcranial magnetic stimulation and transcranial direct current stimulation. We will reflect upon relevant similarities and differences between them, and consider some potentially problematic issues that may arise within the framework of established principles of medical ethics: nonmaleficence and beneficence, autonomy, and justice.

Long-term enhancement of brain function and cognition using cognitive training and brain stimulation

Noninvasive brain stimulation has shown considerable promise for enhancing cognitive functions by the long-term manipulation of neuroplasticity. However, the observation of such improvements has been focused at the behavioral level, and enhancements largely restricted to the performance of basic tasks. Here, we investigate whether transcranial random noise stimulation (TRNS) can improve learning and subsequent performance on complex arithmetic tasks. TRNS of the bilateral dorsolateral prefrontal cortex (DLPFC), a key area in arithmetic, was uniquely coupled with near-infrared spectroscopy (NIRS) to measure online hemodynamic responses within the prefrontal cortex. Five consecutive days of TRNS-accompanied cognitive training enhanced the speed of both calculation- and memory-recall-based arithmetic learning. These behavioral improvements were associated with defined hemodynamic responses consistent with more efficient neurovascular coupling within the left DLPFC. Testing 6 months after training revealed long-lasting behavioral and physiological modifications in the stimulated group relative to sham controls for trained and nontrained calculation material. These results demonstrate that, depending on the learning regime, TRNS can induce long-term enhancement of cognitive and brain functions. Such findings have significant implications for basic and translational neuroscience, highlighting TRNS as a viable approach to enhancing learning and high-level cognition by the long-term modulation of neuroplasticity.

Right but not left angular gyrus modulates the metric component of the mental body representation: a tDCS study

The parietal lobes contribute to body-space representation. The present work aims at characterizing the functional role of the inferior parietal lobe in body-space representation and at studying the different roles of the angular gyrus in the right and left hemisphere. We conducted three separate transcranial direct current stimulation (tDCS) experiments using “tactile distance task” as an implicit measure of body representation. Whereas anodal tDCS on the right angular gyrus influences vocal reaction times (vRT) for stimuli delivered on the ipsilateral body parts without changes of accuracy, right tDCS improved both vRT and accuracy for tactile stimuli on the contralateral limbs. Sham or left parietal anodal tDCS had no effect. These evidences support the view that right parietal areas have a crucial role in the metric component of the body representation.

The mental cost of cognitive enhancement

Noninvasive brain stimulation provides a potential tool for affecting brain functions in the typical and atypical brain and offers in several cases an alternative to pharmaceutical intervention. Some studies have suggested that transcranial electrical stimulation (TES), a form of noninvasive brain stimulation, can also be used to enhance cognitive performance. Critically, research so far has primarily focused on optimizing protocols for effective stimulation, or assessing potential physical side effects of TES while neglecting the possibility of cognitive side effects. We assessed this possibility by targeting the high-level cognitive abilities of learning and automaticity in the mathematical domain. Notably, learning and automaticity represent critical abilities for potential cognitive enhancement in typical and atypical populations. Over 6 d, healthy human adults underwent cognitive training on a new numerical notation while receiving TES to the posterior parietal cortex or the dorsolateral prefrontal cortex. Stimulation to the the posterior parietal cortex facilitated numerical learning, whereas automaticity for the learned material was impaired. In contrast, stimulation to the dorsolateral prefrontal cortex impaired the learning process, whereas automaticity for the learned material was enhanced. The observed double dissociation indicates that cognitive enhancement through TES can occur at the expense of other cognitive functions. These findings have important implications for the future use of enhancement technologies for neurointervention and performance improvement in healthy populations.

Can transcranial electrical stimulation improve learning difficulties in atypical brain development? A future possibility for cognitive training

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Transcranial electrical stimulation (TES) can improve cognitive training effects in adults.

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TES can enhance neuroplasticity from the molecular level to the system level.

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We discuss the usage of TES with cognitive training in atypically developing children.

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We discuss the possible cognitive and physical side effects of TES.

Learning difficulties in atypical brain development represent serious obstacles to an individual's future achievements and can have broad societal consequences. Cognitive training can improve learning impairments only to a certain degree. Recent evidence from normal and clinical adult populations suggests that transcranial electrical stimulation (TES), a portable, painless, inexpensive, and relatively safe neuroenhancement tool, applied in conjunction with cognitive training can enhance cognitive intervention outcomes. This includes, for instance, numerical processing, language skills and response inhibition deficits commonly associated with profound learning difficulties and attention-deficit hyperactivity disorder (ADHD). The current review introduces the functional principles, current applications and promising results, and potential pitfalls of TES. Unfortunately, research in child populations is limited at present. We suggest that TES has considerable promise as a tool for increasing neuroplasticity in atypically developing children and may be an effective adjunct to cognitive training in clinical settings if it proves safe. The efficacy and both short- and long-term effects of TES on the developing brain need to be critically assessed before it can be recommended for clinical settings.

Enhancing Moral Conformity and Enhancing Moral Worth

It is plausible that we have moral reasons to become better at conforming to our moral reasons. However, it is not always clear what means to greater moral conformity we should adopt. John Harris has recently argued that we have reason to adopt traditional, deliberative means in preference to means that alter our affective or conative states directly-that is, without engaging our deliberative faculties. One of Harris' concerns about direct means is that they would produce only a superficial kind of moral improvement. Though they might increase our moral conformity, there is some deeper kind of moral improvement that they would fail to produce, or would produce to a lesser degree than more traditional means. I consider whether this concern might be justified by appeal to the concept of moral worth. I assess three attempts to show that, even where they were equally effective at increasing one's moral conformity, direct interventions would be less conducive to moral worth than typical deliberative alternatives. Each of these attempts is inspired by Kant's views on moral worth. Each, I argue, fails.

Learning and memory

Learning and memory functions are crucial in the interaction of an individual with the environment and involve the interplay of large, distributed brain networks. Recent advances in technologies to explore neurobiological correlates of neuropsychological paradigms have increased our knowledge about human learning and memory. In this chapter we first review and define memory and learning processes from a neuropsychological perspective. Then we provide some illustrations of how noninvasive brain stimulation can play a major role in the investigation of memory functions, as it can be used to identify cause-effect relationships and chronometric properties of neural processes underlying cognitive steps. In clinical medicine, transcranial magnetic stimulation may be used as a diagnostic tool to understand memory and learning deficits in various patient populations. Furthermore, noninvasive brain stimulation is also being applied to enhance cognitive functions, offering exciting translational therapeutic opportunities in neurology and psychiatry.

Using transcranial electrical stimulation to enhance cognitive functions in the typical and atypical brain

Transcranial electrical stimulation (TES) includes methods such as transcranial direct current stimulation, transcranial random noise stimulation, and transcranial alternating current stimulation. These methods provide novel ways of enhancing human cognitive abilities for restorative purposes, or for general cognitive enhancement, by modulating neuronal activity. I discuss here the basic principles behind these methods and provide some illustrations of their efficacy in cognitive enhancement in those with typical and atypical brain function. Next, I outline some future directions for research that are have been largely neglected, such as the issue of individual differences, cognitive side effects, the efficacy of TES for use with healthy elderly populations, children with atypical development, and sports. The results observed thus far with TES as well as its future possibilities have significant implications for both basic and translational neuroscience.

Improvement of the working memory and naming by transcranial direct current stimulation

OBJECTIVE

To investigate the effects of transcranial direct current stimulation (tDCS) applied over the prefrontal cortex on the improvement of verbal, visuospatial working memory and naming in healthy adults.

METHOD

Thirty two healthy adults (15 males and 17 females, mean age 37.3±13.0 years) were enrolled in this study. The subjects were divided into four groups randomly. They underwent sham or anodal tDCS over the left or right prefrontal cortex, for 20 minutes at a direct current of 1 mA. Before and immediately after tDCS, the subjects performed the Korean version of the mini-mental state exam (K-MMSE) and stroop test (color/word/interference) for the screening of cognitive function. For working memory and language evaluation, the digit span test (forward/backward), the visuospatial attention test in computer assisted cognitive program (CogPack®) and the Korean-Boston Naming Test (K-BNT) were assessed before tDCS, immediately after tDCS, and 2 weeks after tDCS.

RESULTS

The stroop test (word/interference), backward digit span test and K-BNT were improved in the left prefrontal tDCS group compared with that of the sham group (p<0.05). The stroop test (interference) and visuospatial attention test were in the right prefrontal tDCS group compared with that of the sham group (p<0.05). Their improvement lasted for 2 weeks after stimulation.

CONCLUSION

tDCS can induce verbal working memory improvement and naming facilitation by stimulating the left prefrontal cortex. It can also improve the visuospatial working memory by stimulating the right prefrontal cortex. Further studies which are lesion and symptom specific tDCS treatment for rehabilitation of stroke can be carried out.

Can tDCS enhance treatment of aphasia after stroke?

BACKGROUND: Recent advances in the application of transcranial direct current stimulation (tDCS) in healthy populations have led to the exploration of the technique as an adjuvant method to traditional speech therapies in patients with post-stroke aphasia. AIMS: THE PURPOSE OF THE REVIEW IS: (i) to review the features of tDCS that make it an attractive tool for research and potential future use in clinical contexts; (ii) to describe recent studies exploring the facilitation of language performance using tDCS in post-stroke aphasia; (iii) to explore methodological considerations of tDCS that may be key to understanding tDCS in treatment of aphasia post stroke; and (iv) to highlight several caveats and outstanding questions that need to be addressed in future work. MAIN CONTRIBUTION: This review aims to highlight our current understanding of the methodological and theoretical issues surrounding the use of tDCS as an adjuvant tool in the treatment of language difficulties after stroke. CONCLUSIONS: Preliminary evidence shows that tDCS may be a useful tool to complement treatment of aphasia, particularly for speech production in chronic stroke patients. To build on this exciting work, further systematic research is needed to understand the mechanisms of tDCS-induced effects, its application to current models of aphasia recovery, and the complex interactions between different stimulation parameters and language rehabilitation techniques. The potential of tDCS is to optimise language rehabilitation techniques and promote long-term recovery of language. A stimulating future for aphasia rehabilitation!

Natural Selection, Childrearing, and the Ethics of Marriage (and Divorce): Building a Case for the Neuroenhancement of Human Relationships

We argue that the fragility of contemporary marriages—and the corresponding high rates of divorce—can be explained (in large part) by a three-part mismatch: between our relationship values, our evolved psychobiological natures, and our modern social, physical, and technological environment. “Love drugs” could help address this mismatch by boosting our psychobiologies while keeping our values and our environment intact. While individual couples should be free to use pharmacological interventions to sustain and improve their romantic connection, we suggest that they may have an obligation to do so as well, in certain cases. Specifically, we argue that couples with offspring may have a special responsibility to enhance their relationships for the sake of their children. We outline an evolutionarily informed research program for identifying promising biomedical enhancements of love and commitment.

Effects of transcranial electrical stimulation on cognition

Alterations of cortical excitability, oscillatory as well as non-oscillatory, are physiological derivates of cognitive processes, such as perception, working memory, learning, and long-term memory formation. Since noninvasive electrical brain stimulation is capable of inducing alterations in the human brain, these stimulation approaches might be attractive tools to modulate cognition. Transcranial direct current stimulation (tDCS) alters spontaneous cortical activity, while transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS) are presumed to induce or interfere with oscillations of cortical networks. Via these mechanisms, the respective stimulation techniques have indeed been shown to modulate cognitive processes in a multitude of studies conducted during the last years. In this review, we will gather knowledge about the potential of noninvasive electrical brain stimulation to study and modify cognitive processes in healthy humans and discuss directions of future research.

tDCS selectively improves working memory in older adults with more education

Cognitive performance, including performance on working memory (WM) tasks declines with age. Changes in brain activations are one presumed contributor to WM decline in the healthy aging population. In particular, neuroimaging studies show that when older adults perform WM tasks there tends to be greater bilateral frontal activity than in younger adults. We hypothesized that stimulating the prefrontal cortex in healthy older adults would improve WM performance. To test this hypothesis we employed transcranial direct current stimulation (tDCS), a neurostimulation technique in which small amounts of electrical current are applied to the scalp with the intent of modulating the activity in underlying neurons. Across three testing sessions we applied sham stimulation or anodal tDCS to the left (F3) or right (F4) prefrontal cortex to healthy older adults as they performed trials of verbal and visual 2-back WM tasks. Surprisingly, tDCS was uniformly beneficial across site and WM task, but only in older adults with more education. In the less educated group, tDCS provided no benefit to verbal or visual WM performance. We interpret these findings as evidence for differential frontal recruitment as a function of strategy when older adults perform WM tasks.

Direct current stimulation (tDCS) reveals parietal asymmetry in local/global and salience-based selection

Data from neuropsychology and neuroimaging studies indicate hemispheric asymmetries in processing object's global form versus local parts. However the attentional mechanisms subtending visual selection of different levels of information are poorly understood. The classical left hemisphere/local-right hemisphere/global dichotomy has been recently challenged by studies linking the asymmetry of activation in the posterior parietal cortex (PPC) with the relative salience of the stimulus rather than with the local/global level. The present study aimed to assess hemispheric asymmetry in local-global and salience-based selection in hierarchical stimuli by using transcranial direct current stimulation (tDCS). To this end, tDCS has been applied to the PPC of both the hemispheres. Our data revealed that tDCS did affect the selection of the target on the basis of its relative salience in a manner that depended on the tDCS polarity applied to the two hemispheres. This result is in line with previous findings that the left PPC is critically involved in attention for low-salience stimuli in the presence of high-salience distractor information, while right PPC is involved in attending to more salient stimuli. Hemispheric asymmetries were also found in local/global selection. Overall the results suggest that neural activation in the PPC is related to both the salience and the level of stimulus representations mediating responses to hierarchical stimuli. The comparison of the results from Experiments 1 and 2 in local/global-based selection suggests that the effect of stimulation could be completely opposite depending on subtle differences in demands of attentional control (sustained attention vs task switching).