6
Enhancement of Brain Function and Performance
Highlights
- Research is expanding on non-therapeutic applications of neurostimulation in healthy people. (Cohen Kadosh, Pascual-Leone)
- Transcranial electrical stimulation can improve cognitive and non-cognitive performance in educational, military, athletic, gaming, and occupational settings, although more evidence is needed to determine its effectiveness. (Cohen Kadosh, Edwards)
- Cognitive and non-cognitive enhancement through neurostimulation may have negative consequences, and the long-term effects have not been well studied. (Fox, Pascual-Leone, Maiques)
- An emerging market for direct-to-consumer non-therapeutic products raises questions about safety and efficacy, as well as attention to safety and efficacy in the home setting. (Wetmore)
NOTE: The points in this list were made by the individual speakers identified above; they are not intended to reflect a consensus among workshop participants.
The effects of non-invasive brain stimulation technologies on cognition and performance has both therapeutic and non-therapeutic applications, depending on whether they are used to ameliorate symptoms of a disorder or enhance otherwise normal function. Indeed, according to Alvaro Pascual-Leone, the range of non-therapeutic applications is growing even faster than therapeutic applications. One reason for the growth of research in this area is that because most investigational interventions are initially tested in groups of healthy individuals before being tested in
patients, most of the available evidence about the effects of these technologies are from healthy subjects, noted Roi Cohen Kadosh.
In addition, a rapidly expanding DIY movement and direct-to-consumer devices are promoting self-experimentation in healthy subjects to enhance abilities and prompting the need for carefully controlled studies to assess effects, evaluate risks, and identify mechanisms
tDCS has been widely used in non-therapeutic applications. However, other types of transcranial electric stimulation are also being used and investigated, including transcranial alternating current stimulation and transcranial random noise stimulation; all of these modalities have different effects on the brain, but ultimately appear to manipulate neuroplasticity (Antal and Paulus, 2013; Fertonani et al., 2011). Moreover, while tDCS appears relatively safe in studies of limited duration, the long-term safety and the long-term effects on the brain have not been well established, according to Ana Maiques and others.
Cognitive enhancement is perhaps the most well known and widely publicized non-therapeutic application of brain stimulation (Coffman et al., 2014). Many studies have shown that TES can improve cognitive and non-cognitive performance with even a single session or multiple sessions of stimulation, particularly when used in combination with cognitive training, said Cohen Kadosh (Cohen Kadosh, 2013). For example, his lab has shown that tRNS, given in combination with two different arithmetical training approaches, improved both the speed of calculation as well as memory-recall-based learning. They further showed that these effects endure for at least 6 months (Snowball et al., 2013). In another study, Reis and colleagues showed that anodal tDCS stimulation over 5 days of training on a visuomotor skill also led to increased learning rate and better performance (Reis et al., 2009). Again, these improvements lasted beyond the neurostimulation period, suggesting a neuroplastic change, said Cohen Kadosh.
Cohen Kadosh noted that most of these studies have focused on young healthy adults. However, his group has also shown that students with math anxiety perform better when they receive tDCS stimulation to the DLPFC. They had not only improved reaction time in comparison to those who received the sham stimulation, but also decreased salivary cortisol concentrations, indicating lower stress. Interestingly, however, when the same stimulation protocol was used in individuals who did not have math anxiety, reaction time increased compared to sham stimulation and cortisol levels increased (Sarkar et al., 2014).
Performance enhancement through neurostimulation is also being actively pursued for military, athletic, educational, gaming, and occupational settings. Dylan Edwards said there is an overwhelming array of applications and many papers published, but few studies replicated. He described one effort to enhance perception using a virtual reality, real-world training application used to train military personnel to detect concealed objects such as bombs (Clark et al., 2012). In this study, tDCS was used to deliver stimulation to brain networks identified by fMRI as important for this task, that is, the right front and parietal cortex. The study in 96 healthy subjects showed that tDCS stimulation resulted in significant improvements in learning and performance, and that these improvements were sustained after training.
Another study designed to investigate the perception of fatigue on performance in elite cyclists showed that tDCS stimulation of the temporal cortex delivered prior to an incremental maximal cycling test resulted in a reduction in heart rate as power increased, and a 4 percent improvement in performance (Okano et al., 2013). The investigators who conducted the study concluded that tDCS modulated the autonomic nervous system and the sensory perception of effort and exercise performance. Edwards said this is important because fatigue is considered a balance between motivation and perception of effort.
In assessing the effects of neurostimulation on cognition, multiple parameters are important, including the cognitive construct of interest, how that construct is measured, when the stimulation is given in relation to the assessment, and the baseline state of the brain, according to Roy Hamilton. Moreover, cognitive enhancement can come with a cost, said Michael Fox. As described in Chapter 3, Fox noted that focal stimulation propagates throughout brain circuits, enabling the stimulation of targets far from the stimulation site. For non-therapeutic use, this propagation can have negative consequences. For example, one might stimulate the DLPFC to enhance cognition, but because of connectivity with limbic regions, the stimulation might also affect mood.
Trade-offs are also seen in studies aimed at improving working memory by stimulating the DLPFC. Pascual-Leone’s lab has shown, for example, that rTMS of the right DLPFC enhanced verbal working memory, but reduced spatial working memory (Fried et al., 2014). Although TMS delivered to the parietal cortex may enhance the ability to detect a visual target on the ipsilateral side, at the same time it can reduce the ability to detect a target on the contralateral side (Hilgetag et al.,
2001). In patients with spatial neglect on one side, this form of therapy may be useful, but should be used with caution in normal subjects.
Non-therapeutic neuromodulation devices are also being developed as direct-to-consumer products, avoiding the regulatory barriers that can slow development of therapeutic products. Throughout the workshop, many participants raised concerns about ethical and safety issues that arise when providing devices outside the medical sphere, However many participants also said that despite these concerns, consumer-targeted devices will represent a substantial part of the market in the future. Ethical issues are discussed further in Chapter 7.
Thync, a neuroscience and consumer technology company based in California and Massachusetts, positions itself outside of the medical or cognitive enhancement spheres, setting as its goal improvement of brain health. Daniel Wetmore, director of intellectual property and usability at Thync, described their device as a wearable Bluetooth® technology controlled unit that snaps into electrodes worn on the temple area of the head with a second electrode either behind the ear or on the back of the neck to deliver electrical stimulation. The company claims its device can modulate psychophysiological arousal by delivering pulsed neurostimulation waveforms (called “Vibes”) to increase energy, enhance focus, boost motivation, reduce stress, and improve the quality of sleep.
In terms of efficacy, Thync has published a preprint in bioRxiv demonstrating that, compared with sham stimulation, the Thync device significantly suppressed the acute stress response without affecting cognition (Tyler et al., 2015). Both self-report and physiologic measures of stress were evaluated. Wetmore said they believe the mechanism of action involves modulation of cranial and cervical spinal nerves with limited direct stimulation of the brain transcranially.