Transcranial alternating current stimulation (TACS) is an emerging non-invasive brain stimulation technique that shows promise for enhancing cognition and treating psychiatric conditions like depression and schizophrenia.
Recent research indicates TACS may improve symptoms and function by modulating brain oscillations and connectivity.
Key facts:
- TACS delivers alternating electrical current to the brain at specific frequencies, which can entrain neural oscillations.
- It may strengthen connectivity between brain regions related to cognition and psychiatric disorders.
- Studies show TACS can enhance cognition in psychiatric patients and possibly healthy people.
- Early evidence points to benefits for depression and schizophrenia symptoms.
- Optimal protocols and long-term side effects need further study.
Source: Ther Adv Chronic Dis (2022)
What is Transcranial Alternating Current Stimulation (TACS)?
Transcranial alternating current stimulation, or TACS, is a non-invasive form of brain stimulation where a weak alternating electrical current is applied to the scalp.
The current passes through the skull to modulate brain waves and activity in specific regions.
TACS is related to other transcranial electrical stimulation (tES) methods like transcranial direct current stimulation (tDCS), but TACS currents oscillate back and forth rather than flowing in one direction.
The oscillating current is delivered at specific frequencies ranging from slow theta waves around 5 Hz to fast gamma waves over 40 Hz.
These stimulation frequencies can synchronize with the brain’s native oscillations, a phenomenon known as neural entrainment.
For example, delivering alpha oscillations around 10 Hz could amplify natural alpha rhythms in the underlying cortex.
TACS may also modulate functional connections between distant brain areas oscillating at the targeted frequency.
Early TACS research focused on manipulating brain oscillations to study cognition and perception in healthy people.
More recently, scientists started exploring whether TACS at key frequencies could improve symptoms in neuropsychiatric disorders with abnormal oscillatory activity.
Potential Mechanisms of TACS: Brain Waves
The precise ways TACS interacts with the brain are still being uncovered, but potential mechanisms include:
- Brain Wave Entrainment – TACS currents can synchronize and amplify the brain’s endogenous rhythms, strengthening natural oscillations.
- Neuroplasticity – Alternating currents may promote neural plasticity, leading to longer-lasting changes in connections.
- Improved connectivity – Stimulation could enhance communication between distant regions oscillating at the targeted frequency.
- Altered excitability – TACS may modify the excitability of neurons, making them more or less likely to generate impulses.
By tuning brain oscillations and connectivity with targeted stimulation frequencies, TACS could temporarily rebalance activity in brain networks disrupted in psychiatric illness.
For example, excess slow oscillations are linked to depressed mood, so stimulating alpha or gamma may help normalize imbalanced rhythms.
TACS for Enhancing Cognition
Abnormal neural oscillations and impaired functional connections between brain areas contribute to cognitive deficits in many psychiatric disorders.
This makes modifying oscillations and connectivity with TACS a promising approach for improving cognition.
So far, research indicates TACS at alpha and gamma frequencies can enhance some aspects of cognition, especially in patients with psychiatric conditions:
- A meta-analysis found TACS significantly improved cognition compared to sham stimulation in psychiatric patients, with benefits seen on tests of memory, attention, processing speed and executive function.
- Studies in Alzheimer’s and mild cognitive impairment patients showed TACS at 40Hz gamma increased verbal learning and memory.
- Alpha TACS around 10 Hz improved working memory performance in schizophrenia patients.
- Some studies in healthy subjects found TACS boosted working memory, attention and other cognitive skills.
While results are preliminary, TACS shows potential to be a safe, non-invasive way to support cognition in both psychiatric patients and healthy people as they age.
Using TACS to Treat Symptoms of Depression
Major depressive disorder afflicts over 16% of adults globally.
Current antidepressant medications have limited efficacy, but neuromodulation approaches like TACS provide new non-pharmacological options.
Growing evidence indicates TACS can reduce depressive symptoms, likely by normalizing aberrant brain oscillations in cortical regions involved in mood regulation:
- A meta-analysis found TACS significantly improved depression severity compared to sham treatment. The benefit was larger than for antidepressant medications in past analyses.
- Multiple studies report that 20-40 Hz gamma TACS over prefrontal areas decreased symptoms and improved mood in depression patients.
- Alpha TACS around 10 Hz also reduced depressive symptoms, with one study showing effects lasting 4 weeks post-treatment.
- Case reports found daily prefrontal gamma TACS induced rapid improvements in depression severity within 5-10 days.
Though larger sham-controlled trials are needed, current research clearly supports TACS as a promising treatment for reducing depressive symptoms, especially at gamma frequencies.
TACS for Schizophrenia Symptoms
Schizophrenia is marked by positive symptoms like hallucinations and delusions as well as negative symptoms like reduced motivation and emotion.
Abnormal low and high frequency oscillations are linked to schizophrenia symptoms.
A few initial studies have tested whether TACS can improve schizophrenia by modulating these oscillations:
- Gamma TACS over prefrontal areas enhanced cognition related to working memory and attention in schizophrenia patients.
- TACS decreased severity of auditory hallucinations compared to sham treatment in one study.
- Schizophrenia patients who received 5 days of frontoparietal TACS showed reduced negative symptoms.
While very few randomized trials have been conducted so far, early findings suggest TACS has potential for managing symptoms like cognitive deficits, hallucinations and flattened affect in schizophrenia. More research is critically needed.
Optimizing TACS Protocols and Parameters
Many factors like electrode placement, current intensity, and stimulation duration and timing can affect TACS results.
Optimization of these parameters will be key for developing effective protocols.
- Electrode locations should target brain regions implicated in the specific cognitive deficits or psychiatric symptoms.
- Current intensity is typically 0.5-2 mA peak-to-peak. Higher intensity may increase effects but also side effects.
- Many studies use 20-40 minute sessions once or twice a day, but more frequent shorter sessions like 2×10 minutes may be beneficial.
- Gamma TACS shows particular promise for depression and cognitive enhancement, while alpha may also improve mood.
- TACS likely needs to be applied repeatedly over multiple sessions to induce lasting benefits.
More studies directly comparing different TACS protocols are essential to determine optimal, personalized stimulation parameters.
TACS: Safety and Side Effects
The limited available evidence indicates TACS is very safe with minimal side effects.
Potential adverse effects include itching, tingling, headache, nausea and light flashes, which are usually mild and resolve quickly after stimulation stops.
TACS requires additional safety testing, but these transient effects suggest it has a much better side effect profile than psychiatric medications.
One key advantage of TACS is that the effects are only present during stimulation, unlike drugs which persist for hours or days after dosing.
However, the long-term impacts of repeated TACS sessions are still unknown. More research is critical to confirm safety with chronic administration.
Future Outlook for TACS in Brain Disorders
Though still an emerging technology, TACS is showing real promise as a novel treatment for boosting cognition and managing psychiatric disease.
TACS research will expand rapidly in coming years to further evaluate efficacy and safety.
If results remain positive, TACS could provide a drug-free alternative for enhancing cognition as we age and managing challenging neurological conditions like depression and schizophrenia.
Combined with improved targeting and personalized protocols, this safe and non-invasive stimulation technique may become an essential new tool in psychiatry and neurology.
References
- Study: Transcranial alternating current stimulation and its effects on cognition and the treatment of psychiatric disorders (systematic review & meta-analysis)
- Authors: Ainsley Ryan Yan Bin Lee et al. (2022)
