That study is misleading/wrong and has done a huge amount of damage to this field.
What they actually showed is that 1) much of the current does not reach the brain, and 2) the current that does is not sufficient to directly “force” neurons to fire. However, that doesn’t mean the remaining current does nothing at all, as it could still modulate brain activity.
Using direct recordings of individual neurons, I showed that various forms of tES shift spike timing. Simulation causes them to fire sooner or later than they otherwise would. This matters because information is carried in both by overall rate of spiking and the timing of those spikes. Moreover, it’s not just a placebo, because knocking out the sensations with topical anesthetic doesn’t block the neural effects, nor is recreating them sufficient to cause them.
I just wrote a little think-piece about this for PLOS Biology that summarizes what we know—-and don’t—-about it
If one wants to change neural computation via a global oscillator, it would seem that a flashing light, auditory tone, or tactile vibration might be a more potent alternative. These stimuli indisputably drive substantial brain wide activity, including many action potentials. I suppose I’m reluctantly team Firing Rate when it comes to mammals—there’s beautiful work on spike ordering in cold blooded animals for example but I’m less aware of computational work where precise spike time matters and not the relative time ie hebbiwn plasticity.
I’m also somewhat influenced by my first hand difficulty when doing in vitro patch clamp to induce sub threshold voltage changes on a neuron with a second probe even just 100um away. Color me skeptical, in part as it’s really hard to do a double-blinded control and the effect sizes seem small.
“Other people tried to put tDCS on a cadaver and said that there wasn’t enough electricity that was penetrating the skull to make any difference in terms of action potentials. But the next meta-analysis found some effectiveness for depression and anxiety. The study[1], published in 2017, was one of the best out there.”
1. https://www.sciencedirect.com/science/article/abs/pii/S13882...
Is it possible to blind test this? Like can people feel whether or not the current is passing through their brain? Feels like it should be easy enough to do a study on
I ran an experiment where we blocked the skin sensations with topical anesthesia and then recorded the responses of individual neurons to tES. Nothing changed, so the sensation is not necessary for its effects.
perhaps the current does not need to actually reach the brain in the way these studies are setup to measure? it’s possible the brain is more sensitive and/or there’s some low powered emf naturally at play in your brain/body, for example
What they actually showed is that 1) much of the current does not reach the brain, and 2) the current that does is not sufficient to directly “force” neurons to fire. However, that doesn’t mean the remaining current does nothing at all, as it could still modulate brain activity.
Using direct recordings of individual neurons, I showed that various forms of tES shift spike timing. Simulation causes them to fire sooner or later than they otherwise would. This matters because information is carried in both by overall rate of spiking and the timing of those spikes. Moreover, it’s not just a placebo, because knocking out the sensations with topical anesthetic doesn’t block the neural effects, nor is recreating them sufficient to cause them.
I just wrote a little think-piece about this for PLOS Biology that summarizes what we know—-and don’t—-about it
https://journals.plos.org/plosbiology/article?id=10.1371/jou...