Transcranial magnetic stimulation (TMS) is a process by which controlled magnetic pulses target a specific area of the brain. In psychiatry, TMS is quickly emerging as a transformative treatment option for major depressive disorder. 

TMS is non-invasive with few side effects. The treatment is extremely tolerable, causing little to no pain in the patient, and does not affect cognition. Not only does this make TMS a promising therapeutic method for those with treatment-resistant depression, but it also means that TMS is incredibly useful from a scientific perspective, as it allows researchers to stimulate the brain without jeopardizing the subject’s well-being. 

In a study published by the National Academy of Sciences, researchers used TMS to investigate affective blindsight— a subject’s ability to correctly respond to a visual cue that is not physically seen by the subject. 

Continue reading for more information regarding: 

• Blindsight 
• The study, including its method and results
• TMS as a psychiatric treatment

Blindsight 

Blindsight occurs when a person with cortical blindness—meaning their primary visual cortex is non-functional—is able to respond correctly to a visual stimuli that is not within their field of vision. According to the neurology journal Brain, patients with blindsight “can accurately detect, discriminate, and localize visual stimuli presented in their blind field, without being able to report any accompanying conscious visual experience.” 

This phenomenon poses many questions to neurologists pertaining to the brain functions that relate to conscious awareness and the repression of unconscious information. Even more questions have been raised after more recent studies found that blindsight can also be found in cases in which facial expressions were used to depict certain emotions. This is known as affective blindsight. 

More About Cortical Blindness

Cortical blindness is a neurological disorder that develops from damage to or obstruction in the visual cortex. Because the visual cortex is responsible for processing the sensory information that the brain receives from the eyes, any trauma that occurs in that part of the brain can affect vision. 

The most common causes of cortical blindness include:

• Hypoxia (occurs when the brain is deprived of oxygen)
• Head injuries
• Abnormalities in brain formation
• Hydrocephalus (fluid and pressure build up in the brain)
• Seizures
• Metabolic diseases
• Infections

The Study

Background

Affective blindsight has been demonstrated using patients with cortical blindness, causing two researchers in the Netherlands to wonder if the same process could be induced in patients with normal vision. 

Method

The study featured ten subjects with normal or corrected-to-normal vision. In order to block signals to the visual cortex, the researchers applied TMS as the subjects were shown happy and sad emoticons on a computer. Because of where the TMS pulses were targeted, the emoticons were rendered effectively invisible to subjects, simulating cortical blindness. 

Results 

In the published study, the researchers write that “the occurrence of TMS-induced affective blindsight depends on overall stimulus visibility: it only occurs when subjects are in a general state of uncertainty about the stimuli.” However, in the end, they still determine that it is possible to induce affective blindsight by applying TMS to the visual cortex. 

TMS as a Psychiatric Treatment

Because the study aimed to simulate cortical blindness in subjects with normal eyesight, the researchers used TMS to obstruct the visual cortex. However, when TMS is administered to other areas of the brain, it can produce different effects. 

In patients with depression, TMS is applied to the prefrontal cortex, which is the area of the brain that regulates mood. Repeated stimulation of this part of the brain can change the way it processes mood and help to relieve symptoms of depression. 

In the study, the subjects only received TMS during the experiment, so the effects they experienced from TMS were only temporary. Because it takes repetitive application over a significant period of time to create a change in the brain with TMS, patients who undergo TMS therapy for depression are required to receive treatments five days a week for around six weeks. 

Again, unlike the individuals in the study, who felt the effects of the TMS immediately upon application, patients being treated with TMS for depression will not feel the results of the therapy instantaneously—though once they do, the results should last a year or more. 

Patients usually experience a change in their depression symptoms a couple weeks into the treatment. Because TMS is non-pharmaceutical, patients taking antidepressants should not have to stop their medication while receiving TMS.

The Innovative Technology of TMS

Part of what makes TMS such a revolutionary technology is the diversity of its real-life applications. Though TMS is currently only FDA-approved to treat major depression disorder and, more recently, obsessive-compulsive disorder, researchers are optimistic that it could have therapeutic benefits for a wide range of mental health conditions, including post-traumatic stress disorder, autism spectrum disorder, bipolar disorder, and more. Additionally, TMS might be able to treat diseases relating to the nervous system like Parkinson’s and tardive dyskinesia. 

From a broader standpoint, TMS is being used to study the brain, as well as different neurological functions—as seen with the study covered in this article. By using TMS as a scientific tool, researchers can learn more about the way our brains and bodies work and, in turn, determine how to better treat conditions that affect these areas.