R Cohen Kadosh

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.

Cognitive Enhancement or Cognitive Cost: Trait-Specific Outcomes of Brain Stimulation in the Case of Mathematics Anxiety

The surge in noninvasive brain stimulation studies investigating cognitive enhancement has neglected the effect of interindividual differences, such as traits, on stimulation outcomes. Using the case of mathematics anxiety in a sample of healthy human participants in a placebo-controlled, double-blind, crossover experiment, we show that identical transcranial direct current stimulation (tDCS) exerts opposite behavioral and physiological effects depending on individual trait levels. Mathematics anxiety is the negative emotional response elicited by numerical tasks, impairing mathematical achievement. tDCS was applied to the dorsolateral prefrontal cortex, a frequent target for modulating emotional regulation. It improved reaction times on simple arithmetic decisions and decreased cortisol concentrations (a biomarker of stress) in high mathematics anxiety individuals. In contrast, tDCS impaired reaction times for low mathematics anxiety individuals and prevented a decrease in cortisol concentration compared with sham stimulation. Both groups showed a tDCS-induced side effect—impaired executive control in a flanker task—a cognitive function subserved by the stimulated region. These behavioral and physiological double dissociations have implications for brain stimulation research by highlighting the role of individual traits in experimental findings. Brain stimulation clearly does not produce uniform benefits, even applied in the same configuration during the same tasks, but may interact with traits to produce markedly opposed outcomes.

Individual differences and specificity of prefrontal gamma frequency-tACS on fluid intelligence capabilities.

Emerging evidence suggests that transcranial alternating current stimulation (tACS) is an effective, frequency-specific modulator of endogenous brain oscillations, with the potential to alter cognitive performance. Here, we show that reduction in response latencies to solve complex logic problem indexing fluid intelligence is obtained through 40 Hz-tACS (gamma band) applied to the prefrontal cortex. This improvement in human performance depends on individual ability, with slower performers at baseline receiving greater benefits. The effect could have not being explained by regression to the mean, and showed task and frequency specificity: it was not observed for trials not involving logical reasoning, as well as with the application of low frequency 5 Hz-tACS (theta band) or non-periodic high frequency random noise stimulation (101-640 Hz). Moreover, performance in a spatial working memory task was not affected by brain stimulation, excluding possible effects on fluid intelligence enhancement through an increase in memory performance. We suggest that such high-level cognitive functions are dissociable by frequency-specific neuromodulatory effects, possibly related to entrainment of specific brain rhythms. We conclude that individual differences in cognitive abilities, due to acquired or developmental origins, could be reduced during frequency-specific tACS, a finding that should be taken into account for future individual cognitive rehabilitation studies.

GABA Predicts Time Perception

Our perception of time constrains our experience of the world and exerts a pivotal influence over a myriad array of cognitive and motor functions. There is emerging evidence that the perceived duration of subsecond intervals is driven by sensory-specific neural activity in human and nonhuman animals, but the mechanisms underlying individual differences in time perception remain elusive. We tested the hypothesis that elevated visual cortex GABA impairs the coding of particular visual stimuli, resulting in a dampening of visual processing and concomitant positive time-order error (relative underestimation) in the perceived duration of subsecond visual intervals. Participants completed psychophysical tasks measuring visual interval discrimination and temporal reproduction and we measured in vivo resting state GABA in visual cortex using magnetic resonance spectroscopy. Time-order error selectively correlated with GABA concentrations in visual cortex, with elevated GABA associated with a rightward horizontal shift in psychometric functions, reflecting a positive time-order error (relative underestimation). These results demonstrate anatomical, neurochemical, and task specificity and suggest that visual cortex GABA contributes to individual differences in time perception.

Modulating and enhancing cognition using brain stimulation: Science and fiction

A new line of research opens the possibility of modulating and enhancing human cognition using mild and painless transcranial electrical stimulation (tES), which includes transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS). Such initial findings trigger excitement as well as scepticism. The current review aims to provide a guideline for those who are interested in expanding their research into this field. I will therefore discuss: (1) the principles of tES and its putative mechanisms; (2) its potential to modulate and enhance cognitive abilities; (3) the misconceptions on which scepticism about this method is based; and (4) possible directions for the advancement of this field in which psychologists in general and cognitive psychologists in particular should in my view play a key role. I will conclude that this nascent field, which has been neglected by psychologists, requires their contribution in order to lead to basic and translational advancements on human behaviour.A new line of research opens the possibility of modulating and enhancing human cognition using mild and painless transcranial electrical stimulation (tES), which includes transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS). Such initial findings trigger excitement as well as scepticism. The current review aims to provide a guideline for those who are interested in expanding their research into this field. I will therefore discuss: (1) the principles of tES and its putative mechanisms; (2) its potential to modulate and enhance cognitive abilities; (3) the misconceptions on which scepticism about this method is based; and (4) possible directions for the advancement of this field in which psychologists in general and cognitive psychologists in particular should in my view play a key role. I will conclude that this nascent field, which has been neglected by psychologists, requires their contribution in order to le...

Transcranial random noise stimulation and cognitive training to improve learning and cognition of the atypically developing brain: A pilot study

Learning disabilities that affect about 10% of human population are linked to atypical neurodevelopment, but predominantly treated by behavioural interventions. Behavioural interventions alone have shown little efficacy, indicating limited success in modulating neuroplasticity, especially in brains with neural atypicalities. Even in healthy adults, weeks of cognitive training alone led to inconsistent generalisable training gains, or “transfer effects” to non-trained materials. Meanwhile, transcranial random noise stimulation (tRNS), a painless and more direct neuromodulation method was shown to further promote cognitive training and transfer effects in healthy adults without harmful effects. It is unknown whether tRNS on the atypically developing brain might promote greater learning and transfer outcomes than training alone. Here, we show that tRNS over the bilateral dorsolateral prefrontal cortices (dlPFCs) improved learning and performance of children with mathematical learning disabilities (MLD) during arithmetic training compared to those who received sham (placebo) tRNS. Training gains correlated positively with improvement on a standardized mathematical diagnostic test, and this effect was strengthened by tRNS. These findings mirror those in healthy adults, and encourage replications using larger cohorts. Overall, this study offers insights into the concept of combining tRNS and cognitive training for improving learning and cognition of children with learning disabilities.

OP 6. Stimulating the brain while playing a computer-based maths game to enhance domain-specific and domain-general cognitive abilities

Introduction Effective processing of the spatial representation of number magnitude is crucial for the development of mathematical skills. Recent research has shown that: (1) bodily spatial experiences of number magnitude resulted in pronounced improvement in numerical development [1] , and (2) competence with fractions predicted gains in mathematical achievement [2] . Objectives We examined here whether cognitive training that included these components coupled with transcranial direct current stimulation (tDCS) could: (1) affect mathematical performance during training; and (2) impact other cognitive functions that are involved in mathematics such as working memory. Materials and methods We designed an adaptive computer-based mathematics game which combined a motion-sensing input device (KINECT™, Microsoft) with wireless tDCS (StarStim, NeuroElectrics) ( Fig. 1 ). We delivered anodal tDCS to the right dorsolateral prefrontal cortex (DLPFC), and cathodal tDCS to the left DLPFC to modulate neuronal excitability and neuroplasticity during the mathematical game. Twenty participants completed two 30-min training sessions on two separate days. They indicated the location of fractions on a visually presented number line by physically moving side-to-side. Trial difficulty increased as a function of performance. Results Compared to sham stimulation, TDCS led to more accurate performance and faster reaction times at higher levels of difficulty. One of the important effects was a dissociation between the success in the game (the highest level reached at the end of training) and mathematical abilities before starting the game ( Fig. 2 ). While the predicted pattern of positive correlation between success in the game and mathematical ability were observed for sham stimulation, in the case of tDCS a negative correlation was observed. Namely, in the tDCS group, those who had lower mathematical abilities were able improve more (i.e., as shown by the levels raised) than those how had higher mathematical abilities prior to training. In addition, tDCS led to a transfer effect in which participants who received tDCS showed after the training a significant increase in verbal working memory performance compared to the sham group, but not on visuospatial working memory. Conclusion Our unique combination of a computer-based mathematics game and brain stimulation has shown to lead to enhanced performance during the training, with an effect on verbal working memory after the completion of the training. In addition, the results indicate the efficacy of tDCS in improving the performance especially of those with less competent mathematical abilities, therefore having important neuroscientific, societal, educational and ethical implications.

The Use of Transcranial Direct Current Stimulation for Cognitive Enhancement

Public and academic debate on the use of noninvasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) as cognitive enhancement proper is on the rise. Critically, the use of such a new approach is contingent on the evidence of its safety, beneficial effects, and its cost-to-benefit ratio at the individual and societal levels. In this chapter we review the basic mechanisms and physiological effects of tDCS, as well as its effects on human cognition across the developmental spectrum in children, adults, and the elderly, in sickness and in health. Then we highlight the parameters that could be further optimized for more effective cognitive enhancement. Finally, we present some of the stimulating and open questions on the future use of tDCS for cognitive enhancement.

Transcranial Electrical Stimulation to Enhance Cognitive Abilities in the Atypically Developing Brain

Individuals with developmental learning disabilities and behavioral disorders show structural and functional abnormalities in certain brain areas, and suffer with severe educational and career consequences. Cognitive interventions show only limited success for improvement. In order to alleviate the burden on the affected individual and the society as a whole, we need to target these neural deficits. Transcranial electrical stimulation (tES), with its large variety of methods to enhance and decrease cortical excitability, is a promising tool to achieve improvements at both brain and behavioral levels. Here we discuss the current options for stimulation and the biological effects, and how these can be applied in some examples of cognitive and behavioral deficits. We also note the importance of safety guidelines and careful assessment in preclinical studies, as well as in clinical pediatric populations, as the evidence in these cases is currently minimal. Overall, we suggest that tES can have the capacity to redirect atypical brain development and have a positive impact on educational difficulties. Future developments in the optimization of training and stimulation parameters might allow us to remove the neural brakes on learning in a variety of child developmental disorders.

Modulating hemispheric lateralization by brain stimulation yields gain in mental and physical activity

Imagery plays an important role in our life. Motor imagery is the mental simulation of a motor act without overt motor output. Previous studies have documented the effect of motor imagery practice. However, its translational potential for patients as well as for athletes, musicians and other groups, depends largely on the transfer from mental practice to overt physical performance. We used bilateral transcranial direct current stimulation (tDCS) over sensorimotor areas to modulate neural lateralization patterns induced by unilateral mental motor imagery and the performance of a physical motor task. Twenty-six healthy older adults participated (mean age = 67.1 years) in a double-blind cross-over sham-controlled study. We found stimulation-related changes at the neural and behavioural level, which were polarity-dependent. Specifically, for the hand contralateral to the anode, electroencephalographic activity induced by motor imagery was more lateralized and motor performance improved. In contrast, for the hand contralateral to the cathode, hemispheric lateralization was reduced. The stimulation-related increase and decrease in neural lateralization were negatively related. Further, the degree of stimulation-related change in neural lateralization correlated with the stimulation-related change on behavioural level. These convergent neurophysiological and behavioural effects underline the potential of tDCS to improve mental and physical motor performance.