Patients usually stare at the machine for a good ten seconds before saying anything. It makes sense. You walk into a psychiatric clinic expecting to talk about your feelings or maybe adjust a medication dosage. Instead, you are looking at a device that resembles a futuristic salon hair dryer or a heavy-duty plastic paddle.
Transcranial Magnetic Stimulation is weird if you think about it too long. Using magnets to change firing patterns in the brain sounds like science fiction. But it works. It relies on the basic principles of Faraday’s law of induction. We pass an electrical current through a coil of wire. That creates a magnetic field. The magnetic field passes through the skull and creates a tiny electrical current in the brain tissue.
Neurons communicate via electricity. If we stimulate them enough, they start to wake up.
But not all magnets are the same. The shape of the coil dictates exactly where that energy goes. This is where things get technical, and it is usually where patients get lost in a sea of clinical jargon.
The Geography of Brain Stimulation
Let’s talk about shapes. In the clinical world, we spend a lot of time analyzing different pulsed electromagnetic geometries. That is just a complicated way of saying “the shape of the metal coil hidden inside the plastic casing.”
The shape dictates the magnetic field. The magnetic field dictates which parts of your brain get stimulated. If you suffer from treatment-resistant depression, the exact location of that stimulation is everything.
For decades, medication was the only real option for severe depressive episodes. Pills wash over the entire brain. They are systemic. TMS is targeted. You sit in a chair. A technician places a device on your head. The machine clicks.
But what device? Usually, it is either a Figure-8 coil or a Deep H-Coil.
The Classic Approach: Figure-8 Coils
The Figure-8 coil has been around for a long time. It is the absolute workhorse of most stimulation clinics.
Imagine two circles of copper wire placed side by side. They look exactly like the number eight. When electricity runs through these two loops, the magnetic fields they generate meet in the middle. The intersection creates a very focused, concentrated point of energy.
Think of it like a magnifying glass focusing sunlight on a single leaf.
Clinicians use this pinpoint accuracy to target the left dorsolateral prefrontal cortex. That is the area of the brain heavily involved in mood regulation. In depressed patients, this area is often underactive. It is asleep at the wheel. The Figure-8 coil knocks on the door and forces it to wake up.
The primary characteristic of the Figure-8 is its focal precision. It hits a small, specific area. The downside? It does not go very deep. The magnetic field usually penetrates about 1.5 centimeters beneath the skull.
For many people, that is enough. The surface stimulation ripples through connecting neural pathways, eventually lifting the depression. But brains are anatomically diverse. Sometimes, the target area sits a little deeper. Sometimes, a highly focused pulse misses the optimal spot by a few millimeters simply because of the natural variations in human skull shape.
Expanding the Field: Deep H-Coil Technology
This brings us to the helmet.
If you see a machine that looks like a padded motorcycle helmet, you are looking at an H-Coil. Specifically, we are talking about deep H coil arrays.
These were developed to solve the depth problem. Researchers figured out that if you wind the copper wires in a complex, three-dimensional web rather than a flat figure-8, you can push the magnetic field further into the brain.
Instead of a magnifying glass, think of it like a floodlight.
An H-Coil sends a broader, deeper magnetic pulse. It can reach up to 3 or 4 centimeters beneath the skull. That might not sound like a massive difference. In brain anatomy, a few centimeters is a completely different zip code.
By going deeper, the H-Coil stimulates a larger volume of tissue. It hits the prefrontal cortex, but it also reaches deeper structures connected to the brain’s reward system. This is why certain H-Coils have FDA clearance for conditions beyond standard depression. Take Obsessive-Compulsive Disorder, for example. OCD involves deeper circuitry in the brain, specifically the anterior cingulate cortex. A shallow, focused pulse struggles to reach those networks effectively. The broader array can get there.
Patients often ask which one is better.
There is no universal answer. It depends entirely on the individual’s anatomy, their specific diagnosis, and how they tolerate the treatment. Some people do incredibly well with the precise tapping of a Figure-8. Others need the broader sweep of the H-Coil to finally see their symptoms lift.
What Happens in the Chair
Knowing the physics is one thing. Sitting in the chair is another.
People get nervous before their first appointment. They expect it to hurt. They expect to feel altered or dizzy. The reality of a TMS session timeline is actually quite boring. That is exactly what you want in a medical procedure.
Your first visit is the brain mapping session. This is where the psychiatrist or technician finds your unique motor threshold. They place the coil over the motor cortex. That is the part of your brain that controls physical movement. They send a single magnetic pulse. They watch your hand.
They adjust the position and the intensity until your thumb twitches involuntarily.
It feels strange. You are not moving your thumb, but it moves anyway. This twitch tells the doctor exactly how much magnetic energy is required to stimulate your specific neurons. Everyone has a different threshold. A thick skull or a different brain fold means you might need a higher dose than the person sitting in the waiting room.
Once they find that threshold, they calculate your treatment dose. Then they move the coil forward to the prefrontal cortex.
The actual treatment takes anywhere from 3 to 20 minutes, depending on the specific protocol being used. You hear a loud clicking sound. It sounds exactly like a woodpecker. You feel a tapping sensation on your scalp.
Some people find the tapping annoying. Some get a mild tension headache afterward. Most people just watch TV or listen to a podcast. You drive yourself home right after. There is no anesthesia. No recovery time.
Navigating Treatment Options
Finding a clinic that understands these nuances is critical. You want a provider who doesn’t just plug you into a machine, but actually evaluates which coil geometry makes sense for your clinical presentation.
If you are looking into Twin Cities TMS, you will find different clinics using different hardware. Some exclusively use Figure-8 paddles. Others invest heavily in H-Coil helmets.
Ask questions. Ask them why they use the equipment they use. A good psychiatrist will gladly explain the reasoning behind their hardware choices. They should be able to articulate why a broad field might benefit your specific type of depression, or why a focal pulse is the better starting point.
Do not accept generic answers. You have a right to know how a magnetic field is going to interact with your nervous system.
The Reality of Clinical Outcomes
Let’s get something straight. Brain stimulation is not a magic wand.
I see a lot of hype online. People call it a miracle cure. That kind of language makes my skin crawl. It sets patients up for massive disappointment.
When you have been depressed for ten years, your brain has literally wired itself to maintain that depression. Neural pathways associated with negative rumination become thick and highly trafficked like highways. Pathways associated with joy, motivation, and executive function become overgrown dirt roads.
Magnetic stimulation forces traffic back onto those dirt roads.
It takes time. You do not walk out of your first session feeling like a new person. Usually, nothing happens for the first two weeks. You just go to the clinic, get your head tapped, and go back to work.
Around week three or four, things shift subtly.
A patient might notice they didn’t hit snooze five times. They might realize they actually laughed at a joke instead of just faking a smile. The heavy, wet blanket of depression starts to thin out.
The geometry of the coil plays a role in how this unfolds.
Because the Figure-8 coil is so focused, placement is critical. If the cap shifts a few millimeters during treatment, the pulse might miss the optimal node of the targeted network. Technicians have to be incredibly meticulous.
The Deep H-Coil is a bit more forgiving with placement. Since the magnetic field is broader, it blankets the general area. If the helmet shifts slightly, the target tissue is likely still getting saturated with the magnetic pulse.
That broad stimulation has a trade-off. Because you are stimulating a larger volume of the brain, some patients report slightly more discomfort on the scalp. There is a slightly higher rate of mild headaches compared to the highly localized Figure-8. The facial nerves might twitch a bit more during the pulse.
It is a constant balancing act between depth, precision, and patient comfort.
Frequency and Firing Rates
The shape of the magnet is only half the equation. The other half is how fast we fire it.
Both H-Coils and Figure-8 coils use rapid pulses to create change. We call this rTMS, which stands for repetitive Transcranial Magnetic Stimulation.
Most standard depression protocols use high-frequency stimulation. We hit the left side of the brain with 10 pulses per second. We call that 10 Hertz. High frequency is excitatory. It wakes up underactive tissue.
Sometimes, we use low-frequency stimulation on the right side of the brain. One pulse per second. Low frequency is inhibitory. It calms down overactive tissue. Anxious depression often involves a hyperactive right prefrontal cortex. Calming it down can reduce the constant state of fight-or-flight many patients live in.
Recently, the field has moved toward Theta Burst Stimulation. This involves firing clusters of pulses incredibly fast. Three pulses at 50 Hertz, repeated five times a second. It mimics the natural theta rhythms of the brain.
Theta burst is highly efficient. A standard session takes about 19 to 37 minutes depending on the machine. A Theta Burst session takes about 3 minutes.
Both coil shapes can deliver these different frequencies. The hardware delivers the pulse, but the software dictates the rhythm. The combination of the right physical geometry and the right firing frequency is what ultimately leads to remission.
Making Sense of the Hardware
At the end of a consultation, a patient usually just wants to know if they are going to get better. They don’t care about Faraday’s law. They don’t care about copper wire configurations. They just want the heavy feeling in their chest to go away.
That is completely fair.
Understanding the tools being used on your brain gives you agency. It helps you ask better questions. If you try a Figure-8 coil for six weeks and do not see a response, you shouldn’t necessarily give up on magnetic stimulation entirely. Your brain might just need the deeper, broader reach of an H-Coil. Or vice versa.
Psychiatry is largely a process of elimination. We gather data, apply a treatment, measure the response, and adjust.
Electro-magnetic treatments are simply another tool. They are a physical intervention for a physical organ. Depression is not a character flaw. It is a biological state. The fact that we can alter that state by waving a shaped magnet over the skull is a massive step forward in medical science.
Talk to your doctor. Look at the equipment. Ask about their mapping process.
Advocate for your own brain. No one else is going to do it for you.
About the Author
