Introduction and History
Noninvasive brain stimulation has been in existence for a long time, but only in the past few years has it been applied to neglect. It has mostly been used in the areas of mental health and motor function. Today, we will be discussing the exciting research that is emerging in this area.
As early as 43 A.D., people have been using electricity to address a variety of health issues. In those days, they did not possess the equipment or the knowledge that we have now. As such, they would take electric torpedo fish and use the electricity they emitted for pain relief. They would apply it directly onto someone's head, if they had migraines. If a person had pain in their arms, feet or hands, they would immerse that particular body part in a bin of water filled with these fish as a means to relieve their pain. This is the earliest recorded history documenting the use of TMS (Transcranial Magnetic Stimulation). This method was continued throughout the 11th century. At one point, they started using electric catfish. They would apply the fish to the frontal bone of patients to try and cure epilepsy. Interesting these medical practices occurred before we had access to modern technology.
Luigi Galvani was the pioneer of electrophysiology. He was the first to discover the existence of electricity in animal tissue. He is known for electrical stimulation experiments that he performed on frogs. Galvani would apply the electrical stimulation, either to the frogs’ muscles directly or to the spinal nerves. Today, it seems obvious that if you stimulate the muscle of the spinal nerve, you are going to get a muscle contraction. Back then, they thought that electricity was outside the nervous system. Galvani was the first to discover that there is electrical activity inside the nervous system. Thus, it was referred to as "galvanism," which gave rise to the modern stimulation techniques that we know today.
Giovanni Aldini (Galvani’s nephew) came along shortly after Galvani. Aldini was interested in galvanism, trying to continue the work of his uncle. Galvani had been stimulating the muscles with the spinal nerves; Aldini was the first to use what Galvani had learned and applied it directly to the human cortex. As gruesome and horrible as it sounds today, at that time, beheadings and executions were commonplace. Townspeople would come and observe these executions, like a spectator sport or a community event. Aldini would go into the town square after an execution and perform shows for the townspeople. He would stimulate the cortex of the decapitated heads, resulting in facial grimaces, and causing them to open their eyes. The townspeople were horrified by this, but at the same time, he drew huge crowds. Later, we discovered that the kind of stimulation he was applying to the cortex was not sufficient to cause muscle contraction. He did not know at the time, but he was stimulating the facial muscles directly. Even so, it still laid the groundwork for modern brain stimulation. The book “Frankenstein” (written by Mary Shelley) was directly inspired by these shows in the town square. Shelley’s quote after witnessing Aldini’s work was, "Perhaps a corpse could be reanimated. Galvanism has shown such things."
This was the first demonstration which ultimately set the groundwork for what we know today as electroconvulsive therapy in patients with mental disorders. Unfortunately, although he was a pioneer in this area, Aldini’s stage shows cast a negative shadow over electrical stimulation experiments. People viewed him as a circus act, or a snake oil salesman – they did not believe his experiments had any validity. As a result, his work was largely ignored for hundreds of years.
Throughout the 19th century, methods became more refined and grew to more closely resemble what we know today as modern brain stimulation. In 1882, Sciamma stimulated the exposed dura mater and he was able to cause muscle contraction in the upper extremities. This is significant because he was able to draw a partial motor map from this work, which we know is important to modern imaging (EEG). Between 1884 to 1886, Alberti elicited upper and lower extremity responses on patients with exposed frontal and parietal lobes, thereby enabling him to further illustrate these motor maps. Finally, in 1980, Merton and Morton developed more of a modern clinical version, where they were able to stimulate the motor and visual cortexes. The problem, however, was that their machinery was not quite as advanced as it needed to be. Pain was very strong for participants because they were using a certain kind of scalp electrode that was uncomfortable with strong levels of stimulation.
Brain Stimulation
That brings us to what we know today as brain stimulation. Many of you are probably familiar with deep brain stimulation. Today, we will not be discussing deep brain stimulation, because we are focused on noninvasive procedures. Deep brain stimulation requires surgery, where they implant electrodes in certain areas of the brain that will produce electrical impulses and regulate abnormal impulses coming from the brain. It is used regularly in people with Parkinson's to improve gait and improve tremors. While they have seen great results with deep brain stimulation, there are risks involved (complications from surgery, infections, etc.). That is where noninvasive brain stimulation fills that gap and provides a safe alternative for patients.
The two kinds that we will focus on today are transcranial direct-current stimulation (tDCS) and transcranial magnetic stimulation (TMS). The basic difference is that tDCS is facilitated by electrodes that are placed on the scalp, which send electric currents into the brain. TMS uses a large coil of wire held next to the head that generates a magnetic field to trigger those electric currents. We will go into more detail later about each of these.
For the purposes of this presentation, I wanted to give a broad overview of neglect in order to set the stage in terms of applying brain stimulation to neglect. We are not going to go into great detail about what goes on with neglect, but I wanted to give a basis.
