Non-Invasive Brain Stimulation for Acquired Brain Injury

Acquired brain injury (ABI) refers to damage to the brain that occurs after birth and is not a result of congenital, hereditary, degenerative, or birth-related trauma. It is a condition that affects millions worldwide, significantly impacting cognitive, physical, and emotional functions. ABI can be caused by both traumatic and non-traumatic events, such as a stroke, tumour, infection, or an external force like a blow to the head.

ABI presents a complex challenge, not only because of the variety of symptoms and effects it causes but also due to the diverse recovery paths different individuals take. Recent advancements in neurorehabilitation, particularly non-invasive brain stimulation (NIBS) techniques like transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS), offer promising treatment options for those affected by ABI.

Understanding Acquired Brain Injury

Acquired brain injury encompasses both traumatic brain injuries (TBI) and non-traumatic injuries, such as those caused by stroke, infections, or anoxia (oxygen deprivation). TBIs result from an external force, such as a fall, car accident, or sports injury, while non-traumatic injuries are usually the result of internal medical conditions. According to the UK Acquired Brain Injury Forum (UKABIF), ABI is neither hereditary nor congenital, meaning it develops later in life due to an event or illness.

Reference:

In the UK, the prevalence of acquired brain injury (ABI) is a significant public health concern. Statistics from the charity Headway reveal that there were 356,699 hospital admissions related to ABI in 2019-20, which amounts to an admission approximately every 90 seconds. This reflects a 12% increase in ABI admissions since 2005-06, highlighting a growing trend in brain injuries requiring medical attention.

These admissions include a range of brain injuries, such as non-superficial head injuries, strokes, brain tumours, and infections like encephalitis. Stroke, in particular, is a major contributor, with 137,403 admissions for stroke alone in 2019-20. Furthermore, the rising incidence of ABI among women is particularly noteworthy, with female head injury admissions increasing by 28% since 2005-06. These statistics underscore the ongoing and escalating demand for comprehensive support services and effective rehabilitation strategies across the UK healthcare system.

Reference:

The implications of ABI are far-reaching, affecting individuals physically, cognitively, and emotionally. These effects can manifest as difficulties with speech and language, problems with memory and concentration, changes in mood or personality, and even physical disabilities. The broad spectrum of symptoms and their severity depend on the location, extent, and cause of the injury, making treatment a complex and multifaceted challenge.

Domains Affected by ABI

The effects of ABI can be seen in several domains, including:

Physical: Individuals may experience weakness, paralysis, or coordination problems. There may also be difficulties with balance and fine motor skills, along with issues related to vision and hearing.
Cognitive: Memory loss, attention deficits, and impaired executive functioning (problem-solving, planning, organising) are common. Communication issues, such as difficulty understanding language or finding words, are also frequently reported.
Emotional/Behavioural: ABI can cause mood swings, depression, anxiety, irritability, and other emotional changes. Some individuals may develop impulsive behaviour, lack of social awareness, or experience inappropriate emotions.

These changes can increase the risk of long-term comorbidities and disease burdens, underscoring the need for effective and comprehensive rehabilitation strategies.

Neurorehabilitation: Traditional Approaches and Challenges

Rehabilitation following ABI typically involves intensive, multidisciplinary approaches aimed at promoting neural plasticity—the brain’s ability to reorganise itself by forming new neural connections. This plasticity is crucial for recovery, as it allows the brain to compensate for damaged areas by reallocating tasks to healthy regions.

Traditional neurorehabilitation often includes activity-based therapies such as:

Physical therapy: To improve movement, balance, and coordination.
Cognitive rehabilitation: Targeting memory, attention, and problem-solving skills.
Speech and language therapy: To address difficulties with communication, speech production, and comprehension.

While these interventions can produce significant improvements in function, the outcomes are often variable. This variability is due to factors such as differences in the frequency and intensity of rehabilitation, as well as patient adherence to treatment plans. Moreover, measuring the effects of neuronal repair can be difficult, further complicating the ability to tailor treatments to individual patients.

Limitations of Traditional Therapies

One of the significant challenges in ABI rehabilitation is the inconsistency in therapeutic interventions. Many rehabilitation programmes lack uniform guidelines on the frequency and duration of treatment sessions, leading to inconsistent results. Additionally, while therapies like physical rehabilitation, speech therapy, and occupational therapy are beneficial, they are not always sufficient on their own.

Pharmacological treatments, often used to manage mood disorders, cognitive dysfunction, or motor deficits in ABI patients, present another challenge. Medications such as antidepressants or antipsychotics can cause adverse side effects, including fatigue, dizziness, or even increased risks of secondary health complications. As such, the medical community has been seeking alternative approaches that minimise these risks while still promoting neuronal recovery.

Non-invasive Brain Stimulation: An Emerging Therapy

Non-invasive brain stimulation (NIBS) has emerged as a promising alternative or adjunct to traditional rehabilitation therapies. Unlike more invasive procedures such as deep brain stimulation (DBS), NIBS techniques like transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) provide a non-surgical means of modulating neural activity.

Repetitive Transcranial Magnetic Stimulation (rTMS)

rTMS is a neuromodulator technique that uses rapidly alternating magnetic fields to regulate activity in specific regions of the brain. A magnetic coil is placed on the scalp, and pulses of magnetic energy are delivered to targeted cortical areas, inducing electrical activity in the neurons beneath. This stimulation can be applied repetitively to produce long-term changes in neural activity.

rTMS can either upregulate or downregulate cortical excitability depending on the frequency of the pulses used. High-frequency stimulation (greater than 5 Hz) increases excitability, while low-frequency stimulation (around 1 Hz) decreases excitability. This flexibility makes rTMS a useful tool in treating various conditions associated with ABI, including mood disorders, cognitive deficits, and motor dysfunctions.

Safety and Risks of rTMS

When applied according to established guidelines, rTMS is considered safe, with few risks of adverse effects. The most common side effects include headaches and minor scalp irritation, which tend to be transient and resolve soon after treatment. However, there is a slightly increased risk of seizures, particularly in individuals with a history of epilepsy, which necessitates careful patient selection and monitoring.

Transcranial Direct Current Stimulation (tDCS)

tDCS is another form of NIBS that uses low-amplitude direct current (usually 1 to 2 milliamps) to modulate cortical excitability. Unlike rTMS, which induces activity through magnetic fields, tDCS works by altering the resting membrane potentials of neurons. Anodal stimulation increases the likelihood of neuronal depolarisation (thus increasing excitability), while cathodal stimulation decreases the likelihood (reducing excitability).

The procedure involves placing electrodes over specific areas of the scalp, with the current passing through the skull to modulate activity in the underlying brain regions. As with rTMS, tDCS has been found to be safe, with only mild and transient side effects, such as headaches or itching at the site of the electrodes. The risk of seizures in individuals without a prior history of epilepsy is considered negligible.

Combining NIBS with Traditional Therapies for Superior Outcomes

One of the key strengths of NIBS is its ability to be integrated with other therapeutic interventions, such as physical therapy, cognitive rehabilitation, and psychotherapy. Research suggests that combining NIBS with traditional therapies can enhance treatment outcomes, as the neuromodulation provided by NIBS facilitates the plasticity that rehabilitation efforts aim to promote.

Evidence from Clinical Studies

Several studies have demonstrated the potential benefits of combining tDCS or rTMS with traditional therapies for ABI rehabilitation.

A review by Zaninotto and colleagues examined the effects of tDCS on recovery following TBI. While the results varied across studies, the authors found that tDCS consistently improved cognitive function when paired with cognitive rehabilitation and enhanced motor recovery when used in conjunction with physical therapy.

Similarly, a study by Lee and Kim investigated the use of low-frequency rTMS to treat depression and cognitive deficits in patients with TBI. Participants were divided into an experimental group, which received low-frequency rTMS to the right dorsolateral prefrontal cortex, and a control group, which received sham rTMS. Both groups underwent neurodevelopmental therapy (NDT) for muscle strengthening and movement re-education, but only the experimental group received active rTMS. The study found that participants who received rTMS showed significant improvements in both depressive symptoms and cognitive performance compared to the control group.

These findings suggest that NIBS not only enhances recovery when used alongside traditional therapies but also contributes to better outcomes in domains such as mood regulation, cognitive function, and motor skills.

Targeting Specific Deficits

In addition to its general benefits for recovery, rTMS has been used to target specific deficits commonly associated with ABI. For example, research has shown improvements in language abilities, such as naming accuracy and word repetition, in patients with aphasia following a stroke or TBI. Similarly, rTMS has been found to improve visuospatial neglect (difficulty perceiving or responding to stimuli on one side of space) in stroke survivors, with patients showing better performance on tasks like line bisection and clock drawing after treatment.

The Future of Non-invasive Brain Stimulation in ABI Treatment

As research continues to explore the potential of NIBS, the future looks promising for the treatment of ABI. The ability of rTMS and tDCS to modulate neural activity in a controlled and targeted manner makes them valuable tools in the rehabilitation process. Moreover, their safety profiles, with few and generally mild side effects, make them an appealing alternative to more invasive.

This post was inspired by a similar article published in the Psychiatric Times. Link to the article: https://www.psychiatrictimes.com/view/treating-acquired-brain-injury-with-noninvasive-brain-stimulation