Krause et al. show that Transcranial Direct Current Stimulates associative learning and alters functional connectivity in the macaque monkey brain:
• tDCS improves animals’ behavior on an associative learning task
• Stimulation has local effects on LFP power and coherence.
• It also causes frequency-specific changes in connectivity between brain areas
• Inter-area coherence in gamma frequencies is linked to behavioral improvement
There has been growing interest in transcranial direct current stimulation (tDCS), a non-invasive technique purported to modulate neural activity via weak, externally applied electric fields. Although some promising preliminary data have been reported for applications ranging from stroke rehabilitation to cognitive enhancement, little is known about how tDCS affects the human brain, and some studies have concluded that it may have no effect at all. Here, we describe a macaque model of tDCS that allows us to simultaneously examine the effects of tDCS on brain activity and behavior. We find that applying tDCS to right prefrontal cortex improves monkeys’ performance on an associative learning task. While firing rates do not change within the targeted area, tDCS does induce large low-frequency oscillations in the underlying tissue. These oscillations alter functional connectivity, both locally and between distant brain areas, and these long-range changes correlate with tDCS’s effects on behavior. Together, these results are consistent with the idea that tDCS leads to widespread changes in brain activity and suggest that it may be a valuable method for cheaply and non-invasively altering functional connectivity in humans.
Grossman et al. (Open Access) describe the use of multiple external high frequency electric fields to generate electric field envelopes inside the brain that can stimulate neurons. This could potentially substitute for current stimulation therapies for Parkinson’s disease, depression, and obsessive-compulsive disorder that require implanting electrodes in the brain.
And, an opinion article by Diana et al. discusses rehabilitation of the addicted brain with transcranial magnetic stimulation.