TMS for Bipolar: Breaking Down Innovative Treatment Approaches

Transcranial magnetic stimulation (TMS) is emerging as a potential treatment for bipolar disorder, providing an alternative for those who have not responded well to medication or therapy. While primarily used for depression, research suggests it may help regulate mood instability in bipolar patients by targeting brain regions involved in emotional processing.

As interest in TMS grows, understanding its mechanisms and different approaches is essential. This article explores how TMS works, the steps involved in a session, and the various treatment modalities available.

Basic Principles Of TMS

TMS delivers focused magnetic pulses to specific brain areas, influencing neural activity without invasive procedures. This technique relies on electromagnetic induction, where a rapidly changing magnetic field generates electrical currents in targeted cortical regions. For bipolar disorder, TMS is primarily directed at the dorsolateral prefrontal cortex (DLPFC), a region implicated in mood regulation and executive function. Functional MRI and electroencephalography studies show that individuals with bipolar disorder often have dysregulated activity in this area, contributing to mood instability. By modulating neural excitability, TMS aims to restore balanced brain function and alleviate symptoms.

The effectiveness of TMS hinges on its ability to induce neuroplastic changes—alterations in synaptic strength and connectivity that support long-term mood regulation. Research indicates that repeated stimulation enhances synaptic efficacy by promoting the release of neurotransmitters like glutamate and gamma-aminobutyric acid (GABA), both crucial for mood stability. TMS also influences brain-derived neurotrophic factor (BDNF) levels, a protein essential for neuronal survival and synaptic plasticity. A 2022 meta-analysis in JAMA Psychiatry found that individuals receiving TMS exhibited increased BDNF expression, correlating with symptom improvement.

Beyond neurotransmitter modulation, TMS affects large-scale brain networks involved in emotional processing. The DLPFC is a central node in the fronto-limbic circuit, which includes the amygdala, anterior cingulate cortex, and hippocampus—regions often hyperactive or hypoactive in bipolar disorder. Stimulating the DLPFC can indirectly regulate activity in these deeper structures, leading to more stable emotional responses. Neuroimaging studies show that after a course of TMS, bipolar patients exhibit normalized connectivity between the prefrontal cortex and limbic system, suggesting a rebalancing of neural circuits that govern mood. This modulation is particularly relevant for individuals with rapid mood cycling, as it may help reduce excessive neural fluctuations contributing to emotional instability.

TMS Session Steps

Before starting a TMS session for bipolar disorder, a thorough evaluation determines the appropriate stimulation parameters. This process involves mapping the motor cortex to establish the resting motor threshold (RMT), which calibrates the intensity of magnetic pulses. The RMT is identified by applying brief magnetic stimuli to the scalp and observing the minimal intensity needed to elicit a motor response, typically a twitch in the thumb or fingers. Advanced neuro-navigation systems, often incorporating MRI scans, refine this process by pinpointing the precise location of the DLPFC, the primary target for TMS in mood disorders.

Once parameters are set, the patient is seated, and a coil is positioned over the treatment site. The coil generates rapid magnetic pulses that penetrate the scalp and skull to reach cortical neurons. The sensation is often described as a tapping or tingling on the scalp, though most individuals acclimate within the first few sessions. Throughout the procedure, the technician monitors for discomfort and adjusts settings if necessary. Sessions typically last between 20 to 40 minutes, depending on the protocol. Some protocols use high-frequency stimulation (e.g., 10 Hz) to enhance cortical excitability, while others use low-frequency pulses (e.g., 1 Hz) to reduce excessive neural activity. The choice of frequency depends on symptomatology, with depressive episodes often treated with excitatory stimulation and manic symptoms potentially requiring inhibitory approaches.

Unlike electroconvulsive therapy (ECT), TMS does not require anesthesia, and cognitive function remains intact. Some individuals report mild side effects, such as scalp discomfort or transient headaches, but these typically subside after the first few treatments. To maximize benefits, sessions are conducted five days a week over four to six weeks, following established clinical guidelines. A 2021 study in The American Journal of Psychiatry found that adherence to a full treatment course significantly improved symptom relief, with response rates exceeding 50% in patients with treatment-resistant mood disorders.

TMS Modalities

Different TMS modalities optimize treatment outcomes for bipolar disorder by varying stimulation depth, frequency, and pattern. These approaches enhance therapeutic effects while minimizing side effects, offering tailored interventions based on individual symptom profiles. The three primary modalities are repetitive TMS (rTMS), deep TMS (dTMS), and theta burst stimulation (TBS), each with distinct mechanisms and clinical applications.

Repetitive TMS

Repetitive transcranial magnetic stimulation (rTMS) delivers a series of magnetic pulses at a fixed frequency to modulate neural activity. High-frequency rTMS (typically 10 Hz) enhances excitability in the DLPFC, which is often underactive in bipolar depression. Conversely, low-frequency rTMS (1 Hz) can help reduce hyperactivity in certain cortical areas, benefiting individuals experiencing manic symptoms. A 2022 randomized controlled trial in Brain Stimulation found that high-frequency rTMS significantly improved depressive symptoms in bipolar patients, with response rates comparable to those in unipolar depression. The non-invasive nature of rTMS and its ability to induce neuroplastic changes make it a promising option for those unresponsive to conventional treatments.

Deep TMS

Deep transcranial magnetic stimulation (dTMS) uses specialized H-coils to penetrate deeper cortical and subcortical structures, reaching brain regions beyond the superficial cortex. Unlike standard rTMS, which primarily affects the DLPFC, dTMS can stimulate areas such as the anterior cingulate cortex and insula, both involved in emotional processing and cognitive control. A 2021 study in Neuropsychopharmacology found that dTMS targeting the medial prefrontal cortex led to significant mood stabilization in bipolar patients, particularly those with treatment-resistant depression. The broader stimulation field of dTMS may benefit individuals with complex symptom presentations, though careful calibration is needed to avoid overstimulation of adjacent brain regions. While generally well tolerated, dTMS may cause mild headaches or scalp discomfort, similar to conventional TMS approaches.

Theta Burst Stimulation

Theta burst stimulation (TBS) delivers bursts of magnetic pulses in a pattern mimicking natural brain rhythms associated with synaptic plasticity. This approach can be administered in intermittent (iTBS) or continuous (cTBS) forms, with iTBS enhancing cortical excitability and cTBS producing inhibitory effects. A key advantage of TBS is its shorter session duration—typically around three minutes—compared to traditional rTMS protocols. Research published in Biological Psychiatry in 2022 indicated that iTBS was as effective as conventional high-frequency rTMS for bipolar depression, with similar response rates but greater patient convenience. The rapid stimulation pattern of TBS may enhance neuroplasticity more efficiently, potentially leading to faster symptom improvement. However, as a relatively recent modality, further studies are needed to refine its application in bipolar disorder treatment.