Mind machines – the promise and problems of cognitive enhancement devices

In this video Roi Cohen Kadosh (Professor of Cognitive Neuroscience at the University of Oxford) likens the use tDCS without a task and purpose, to an athlete taking steroids and not exercising. He discusses recent papers coming out of his lab and describes the research that resulted in this paper: Combining brain stimulation and video game to promote long-term transfer of learning and cognitive enhancement. Kadosh points out that while tDCS did enhance performance in a math challenge, it simultaneously had a negative impact on another. Following Kadosh, Dr Hannah Maslen discusses DIY and DTC tDCS in the context of regulation in the EU.

Those who received real tDCS performed significantly better in the game than the sham group, and showed transfer effects to working memory, a related but non-numerical cognitive domain. This transfer effect was absent in active and sham control groups. Furthermore, training gains were more pronounced amongst those with lower baseline cognitive abilities, suggesting the potential for reducing cognitive inequalities. All effects associated with real tDCS remained 2 months post-training. Our study demonstrates the potential benefit of this approach for long-term enhancement of human learning and cognition.

Older adults get episodic memory boosting from noninvasive stimulation of prefrontal cortex during learning

Great example of exactly what we’re up against. The study in the previous post found no effect on Working Memory in older adults targeting dorsolateral prefrontal cortex (dlPFC). This study did find a positive effect on Episodic Memory in older adults targeting left lateral prefrontal cortex (PFC).

Episodic memory displays the largest degree of age-related decline, a process that is accelerated in pathological conditions like amnestic Mild Cognitive Impairment (aMCI) and Alzheimer’s Disease (AD). Previous studies have shown that the left lateral prefrontal cortex (PFC) contributes to the encoding of episodic memories along the life span. The aim of this randomized, double-blind, placebo-controlled study was to test the hypothesis that anodal tDCS over the left lateral PFC during the learning phase would enhance delayed recall of verbal episodic memories in elderly individuals. Older adults learned a list of words while receiving anodal or placebo (sham) tDCS. Memory recall was tested 48 hours and 1 month later. The results showed that anodal tDCS strengthened episodic memories, an effect indicated by enhanced delayed recall (48 hours) compared to placebo stimulation (Cohen’s d effect size=1.01). The observation that PFC-tDCS during learning can boost verbal episodic memory in the elderly opens up the possibility to design specific neurorehabilitation protocols targeted to conditions that affect episodic memory such as MCI.

No Significant Effect of Prefrontal tDCS on Working Memory Performance in Older Adults

Improved working memory is why many of us are interested in tDCS. Here’s another study showing no effect. Looks like a good study, though it’s a single-session of tDCS. Of late I’ve noticed more studies targeting working memory using the N-back test to measure. I’m hopeful a protocol will be discovered (i.e. a different montage, dosage, or perhaps tACS) that does improve working memory.

Transcranial direct current stimulation (tDCS) has been put forward as a non-pharmacological alternative for alleviating cognitive decline in old age. Although results have shown some promise, little is known about the optimal stimulation parameters for modulation in the cognitive domain. In this study, the effects of tDCS over the dorsolateral prefrontal cortex (dlPFC) on working memory performance were investigated in thirty older adults. An N-back task assessed working memory before, during and after anodal tDCS at a current strength of 1mA and 2mA, in addition to sham stimulation. The study used a single-blind, cross-over design. The results revealed no significant effect of tDCS on accuracy or response times during or after stimulation, for any of the current strengths. These results suggest that a single session of tDCS over the dlPFC is unlikely to improve working memory, as assessed by an N-back task, in old age.

Source: No Significant Effect of Prefrontal tDCS on Working Memory Performance in Older Adults

Longitudinal Neurostimulation in Older Adults Improves Working Memory | PLOS ONE


Modeling of current flow when applying 1.5 mA tDCS for F4 anodal (top) and P4 anodal (bottom) stimulation and the cathodal electrode placed on the contralateral cheek.

Important study. 72 older participants, average age 64 showed improvement in working memory tasks but also (and this is a big deal where it comes to cognitive enhancement) significant transfer (where improvements are seen in other tasks not specifically trained for). These results run counter to other recent studies and beg the question of whether the participant’s age was a factor. i.e. Is tDCS more effective for aging brains? That would be a big deal. [See Also: tDCS selectively improves working memory in older adults with more education]  And thanks to PLOS ONE we can all read the full paper (linked below)

The results demonstrated that all groups benefited from WM training, as expected. However, at follow-up 1-month after training ended, only the participants in the active tDCS groups maintained significant improvement. Importantly, this pattern was observed for both trained and transfer tasks. These results demonstrate that tDCS-linked WM training can provide long-term benefits in maintaining cognitive training benefits and extending them to untrained tasks.

Interesting, the location of the reference (cathodal) electrode was opposite cheek.

In all conditions, one electrode was placed over the target location at either F4 or P4 (International 10–20 EEG system) and the reference electrode was placed on the contralateral cheek.

via PLOS ONE: Longitudinal Neurostimulation in Older Adults Improves Working Memory.

Hits and misses: leveraging tDCS to advance cognitive research

Excellent study. Confirming once again how early we are in our understanding of tDCS. (emphasis below are mine).

Although these studies all report positive findings there is still considerable variability in terms of the pattern of effects, paradigms used and tDCS parameters. For instance, stimulus intensity, duration, tDCS electrode montage are inconsistent. The most consistent pattern in the published literature has been to report significant improvements in WM tested in verbal n-back tasks and anodal tDCS to the left DLPFC. In other cognitive realms a patchwork of findings is emerging revealing consistent effects in memory, deception, and cognitive control. However, there are exceptions and forays into different tasks, populations, and parameters have produced different patterns of results.

via Hits and misses: leveraging tDCS to advance cognitive research.

Recent tDCS Papers of Interest

  1. Acute working memory improvement after tDCS in antidepressant-free patients with Major Depressive Disorder. All effect sizes were large. In other words, one session of tDCS acutely enhanced WM in depressed subjects…(Paywall)
  2. Neurobiological Effects of Transcranial Direct Current Stimulation: A Review The purpose of this systematic review is to summarize the current knowledge regarding the neurobiological mechanisms involved in the effects of tDCS. (pdf)
  3. Modulating Human Procedural Learning by Cerebellar Transcranial Direct Current Stimulation. Our finding that anodal cerebellar tDCS improves an implicit learning type essential to the development of several motor skills or cognitive activity suggests that the cerebellum has a critical role in procedural learning. (Paywall)
  4. Neuroenhancement of the aging brain: Restoring skill acquisition in old subjectsThese results suggest noninvasive brain stimulation as a promising and safe tool to potentially assist functional independence of aged individuals in daily life. (Paywall)
  5. Examining transcranial direct-current stimulation (tDCS) as a treatment for hallucinations in schizophrenia. Although this study is limited by the small sample size, the results show promise for treating refractory auditory verbal hallucinations and other selected manifestations of schizophrenia. (Paywall)
  6. Modulation of training by single-session transcranial direct current stimulation to the intact motor cortex enhances motor skill acquisition of the paretic hand.These results indicate that tDCS is a promising tool to improve not only motor behavior, but also procedural learning. (Paywall)
  7. Interactions between transcranial direct current stimulation (tDCS) and pharmacological interventions in the Major Depressive Episode: Findings from a naturalistic study. tDCS over the DLPFC acutely improved depressive symptoms. Besides the inherent limitations of our naturalistic design, our results suggest that tDCS effects might vary according to prior pharmacological treatment… (Paywall)
  8. Amelioration of Cognitive Control in Depression by Transcranial Direct Current StimulationDeficient cognitive control over emotional distraction is a central characteristic of major depressive disorder (MDD). The present study demonstrates that anodal tDCS applied to the left dlPFC improves deficient cognitive control in MDD. (Paywall)
  9. Comparing immediate transient tinnitus suppression using tACS and tDCS: a placebo-controlled study. Our main result was that bifrontal tDCS modulates tinnitus annoyance and tinnitus loudness… (Paywall)
  10. Review of transcranial direct current stimulation in poststroke recovery. In this review, we summarize characteristics of tDCS (method of stimulation, safety profile, and mechanism) and its application in the treatment of various stroke-related deficits… (Paywall)
  11. Enhancing vigilance in operators with prefrontal cortex transcranial direct current stimulation (tDCS)These findings indicate that tDCS may be well-suited to mitigate performance degradation in work settings requiring sustained attention or as a possible treatment for neurological or psychiatric disorders involving sustained attention. (Paywall)


Anodal transcranial direct current stimulation of prefrontal cortex enhances working memory – Springer

[Update 12/17/2012 Another paper discussing the efficacy of using tDCS to enhance working memory. Transcranial direct current stimulation of the prefrontal cortex modulates working memory performance: combined behavioural and electrophysiological evidence]

Working memory, as associated with ‘brain training’ and ‘plasticity‘, is often expressed as what one would wish to have more of, or at the very least, what one hopes not to lose as we age. (For a great overview of working memory and the how’s of enhancing it, see this fascinating post from neuroscientist Bradley Voytek’s blog  Working memory and cognitive enhancement.)

Our aim was to determine whether anodal transcranial direct current stimulation, which enhances brain cortical excitability and activity, would modify performance in a sequential-letter working memory task when administered to the dorsolateral prefrontal cortex DLPFC. Fifteen subjects underwent a three-back working memory task based on letters. This task was performed during sham and anodal stimulation applied over the left DLPFC. Moreover seven of these subjects performed the same task, but with inverse polarity cathodal stimulation of the left DLPFC and anodal stimulation of the primary motor cortex M1. Our results indicate that only anodal stimulation of the left prefrontal cortex, but not cathodal stimulation of left DLPFC or anodal stimulation of M1, increases the accuracy of the task performance when compared to sham stimulation of the same area. This accuracy enhancement during active stimulation cannot be accounted for by slowed responses, as response times were not changed by stimulation. Our results indicate that left prefrontal anodal stimulation leads to an enhancement of working memory performance. Furthermore, this effect depends on the stimulation polarity and is specific to the site of stimulation. This result may be helpful to develop future interventions aiming at clinical benefits.

via Anodal transcranial direct current stimulation of prefrontal cortex enhances working memory – Springer.
full pdf

This 2011 paper does confirm positive results of tDCS in a similar application and test setup. Improving working memory: exploring the effect of transcranial random noise stimulation and transcranial direct current stimulation on the dorsolateral prefrontal cortex.

However, the study does provide confirmation of previous findings that anodal tDCS enhances some aspects of DLPFC functioning.