Electricity and brain stimulation

Electricity is the basis of neural and muscular functioning. It’s how neurons communicate with one another and messages are being sent by electricity. These signals in the brain can be measured invasively (from inside the brain) or from the outside, like from the scalp. Neural signals can be influenced by excitation, inhibition and desynchronization. This can be done by machineries. An example is a pacemaker in the heart. This machinery is a widely accepted form of muscular stimulation. When it comes to the brain, people feel more uncomfortable with the thought of having such a machinery inside their brains.

There are two main forms of brain stimulation. Invasive stimulation is done from inside the head. Examples of this form of brain stimulation are Deep Brain Stimulation (DBS), as used in Parkinson, and Cochlear Implants (CI). Non-invasive stimulation is done from outside the head, for example placing electrodes onto the scalp. Examples of this form of brain stimulation are Transcranial Direct Current Stimulation (tDCS) and Transcranial Magnetic Stimulation (TMS, rTMS).

Functions of brain stimulation are restoring function (stimulating something until it works by itself again), replacing function (adding something to take the place of the specific organ), improving function and research.

Deep Brain Stimulation

With DBS, electrodes are deeply implanted and those can record activity, but deliver stimulation as well. It can be used in diseases like Parkinson, chronic pain, major depression, OCD, Tourette and perhaps epilepsy (more research is needed). The placement and calibration of the device depend on the clinical goal. It must be done very precisely and it is important to know what kind of stimulation is needed (e.g. OCD needs different stimulation than major depression). Everyone’s brain is different from one another, therefore many scans is research is needed to figure out what is where exactly and where to put the stimulation.

There are some issues and challenges within DBS. It is invasive and very expensive. The underlying mechanisms are unknown. We don’t know exactly how it works and therefore more research is needed. Potential mechanisms are depolarization blockade, synaptic inhibition and desynchronization. There is also the risk of haemorrhage and/or infections. When someone is eligible for DBS, you must look at the level of disability (e.g. is the tremor severe enough to get the surgery?), age (elderly are more vulnerable) and the neuropsychiatric profile.

Cochlear implants

A cochlear implant is a device that stimulates the nerves inside the cochlea. It is widely used: approximately 600.000 people worldwide in 2016 got the surgery. A cochlear implant consists of two parts. There’s an external microphone/sound processor and transmitter, which is visible (placed onto the scalp), and there’s an implanted recover and stimulator (‘the receiver’). This receiver sends signals to the electronic device inside the cochlea. The transmitter and receiver are connected with magnets through the skin.

Many users are children, because a cochlear implant can make a big difference in developing skills like language. Yet, the sound is still very degraded ant it makes it hard and exhausting to keep listening and figuring out what is being said.

Transcranial Direct Current Stimulation (tDCS)

A tDCS is a device which consists of two parts, which are placed on either side of the head, which produce a current flow through the brain. Claims made that by running current through the brain, brain areas are ‘activated’. There are many DIY applications as well, but by using a tDCS, working memory decreases. Arguments against DIY tDCS, written in an open letter concerning DIY tDCS are:

• Stimulation affects more of the brain than a user might think
• Stimulation interacts with ongoing brain activity and tasks during tDCS changes its effects
• Enhancement of some cognitive abilities may come at the cost of others
• Changes in brain activity (intended or not) may last longer than a user may think
• Small differences in tDCS parameters can have a big effect
• tDCS effects are highly variable across different people
• the risk/benefit ratio is different for treating diseases than for enhancing function

Transcranial Magnetic Stimulation (TMS)

TMS is used for mild activations or reversible ‘lesions’. The magnetic pulse produced temporarily activates or disables a brain region. The frequency and intensity of magnetic pulses are adjusted to the specific stimulation aim, either inhibition or excitation. Localisation of the pulses is based on the coordinate system. Sometimes they use an individual T1 MRI scan if they want to know about a specific brain area and where the pulse should go. The coil can be placed just where the pulse should go. The effects of TMS can be instantaneous and inhibition can be made to last up to an hour. Treatment consists of multiple, sometimes daily sessions over several weeks (4-6), and the effects last up to 6 months or longer. rTMS stands for repetitive TMS.

Clinical goals

Clinical goals are restoring function, replacing function and improving function. Restoring function is done by adding stimulation until a brain or network is affected by disease or damage can function independently again. This method is typically (and ideally) non-invasive. Replacing function is done by applying stimulation in the absence of normal function, without expectation that this function will return. This method is invasive. Methods used are cochlear implants and DBS. Improving functions is done by applying stimulation to increase functionality in the absence of clinically designated issues and is usually done for non-clinical problems. Some people want to use tDCS to improve their cognition or motor behaviour, but they often don’t oversee the consequences of such a brain surgery. This method is necessarily non-invasive.

Research goals

Manipulation of variables allows for causal reasoning in neuroimaging research and therefore we can learn more about the brain and diseases. Learning about the brain is usually done by using TMS and it gives a contribution of a specific region to a specific function. Learning about diseases is usually done by using TMS or DMS, and it is mostly geared towards treatment.

Specific research designs are needed and control groups are extremely important, so the participants will not know whether their brain areas are being stimulated or not.

General considerations for implants and stimulation

Implants and stimulation give interesting findings, sometimes with very clear clinical relevance, and implants and stimulation give high impact for users. But the working mechanisms are often unclear, implantation is risky and the side effects can be unpredictable.

Summary part 1: Technology and the brain

• The brain’s electrical activity can be modulated using invasive and non-invasive electrodes that deliver a current
  • Invasive electrodes need to be implanted, sometimes have an external control but sometimes work continuously
  • Non-invasive stimulation can be applied through magnetic pulses or direct currents
• Brain stimulation can serve different goals
  
  • Restoration, replacement, enhancement
  • Goal also drives the tolerance for risk
• Fast-moving research field
  
  • Expanding the clinical issues that are addressed
  • Increasing possibilities for commercial marketing for home use

Brain-Computer Interface (BCI)

Brain-Computer Interface is a mechanism in which computers interact with the brain. A lot of these methods are aimed at people suffering from the so called locked-in syndrome. These people are completely paralyzed but still awake. This method is also aimed at people who are not completely locked in, for example if they are paralyzed from the neck down.

Goals of BCI are for example driving a wheelchair, driving a robot arm, controlling a cursor on a screen, selecting letters or words to communicate or to control the environment (controlling lights, curtains or TV).

Within BCI, the subject or patient is thinking something, or has an idea of the output they want, which might be related to an offered stimulus). At the same time, some type of brain measure has to be taken (MRI, EEG, LOC). Many analyses on brain data are made to make it ready for classifying and looking for features (are you looking for a particular response?).

Slow cortical potentials

You can be trained to produce specific brain potentials that are easy to measure. By rewarding specific brain responses people can learn how to produce them. However, it is in implicit process and it takes long training time. This training time is sometimes prohibitively long for people with degenerative disorders, like ALS. Those patients do not always have the time to do the training, and besides, a patient’s situation will change over time as well.

BCI: cognitive tasks

EEG is the most obvious choice (portable, relatively cheap) to detect and convert to communication to give a brain signal. Event-related potentials (ERP) or visual potentials (p300) methods are often used (EEG features). Other tasks are mental arithmetic tasks and navigation imagery tasks. Whatever is reliably detectable could be used for BCI, but the risk depends on the output.

Visual P300 BCI is a method in which occipital response is measureable in EEG when you see a flash. By looking at a letter in a matrix, with rows and columns flashing, the system can determine which letter was looked at. Once the letter has flashed 2-20 times, attention to it can be detected.

Motor imagery BCI is a method in which when imagining or intending movement, an EEG signal is produced that looks like actual movement. Beta frequencies desynchronize during movement imagery and resynchronize afterwards, and even hand and foot movement imagery can be distinguished.

Neurofeedback/neural biofeedback

Modulation of brain activity through feedback learning is based on operant conditioning. There is an enormous range of disorders claimed to be positively affected, like ADHD, pain, anxiety, psychopathy, epilepsy and strokes. There is evidence for use in ADHD (comparable to pharmacological treatment), but many types of neurofeedback have not yet been fully investigated.

When recovering from a stroke, rehabilitation BCI is used instead of assistive BCI. Rehabilitation BCI aims to stimulate neuroplasticity and facilitate recover rather than replacing a certain function. This method is especially useful for people who are in chronic phases of rehabilitation, since most people regain their functions in the first phases after the stroke, but after 3-6 months people don’t really recover anymore and will suffer from e.g. upper limb impairment.

BCI: other imaging methods

Other imaging methods are fMRI neurofeedback, NIRS neurofeedback and MEG. fMRI neurofeedback is used for various clinical purposes. It gives treatment for potential phobias, mood disorders, smoking cessation and eating disorders. It provides self-regulation of specific brain areas. NIRS neurofeedback provides superficial oxygen use and MEG is similar to EEG, but much less portable.

Summary part 2

• Brain-computer interfaces use real-time measures of brain activity to produce an output
  • Multiple types of input in terms of cognitive tasks
  • Multiple types of output in terms of what is controlled
• Meant to address Locked-In Syndrome
  
  • Result of ALS, brain injury of other disease leading to tetraplegia
• Most common method of brain imaging is EEG or implanted electrodes      
  
  • Implications for conditions of use
• Main mechanisms dependent on imagery tasks, selective attention or neurofeedback
• Greatly increasing speeds of transmission
  
  • Starting to compete with methods using eye movements or suck/blow switches
• Huge implications for individuals, unclear how broadly applicable the technology is
• Ethical implications: agency, (dis-)ability, inclusivity

Innovations in neuropsychology: future and now

There has been a huge development in neuropsychology. Technology is increasingly used for various neuropsychological goals, like giving diagnosis, interventions and compensation.

Most neuropsychological tests are still pencil-and-paper, but there have been many new opportunities in electronic testing, which precisely measure timing and location on screens.

There are many new interventions in stimulation, training (serious gaming (for goals like cognition and exercise), virtual reality) and (tele-)rehabilitation (individualised programs, online and device based).