Please note: This type of neurofeedback training has limited scientific evidence and at this stage is not considered an efficacious treatment for any specific disorders.
What is Slow Cortical Potential Training?
Slow Cortical Potentials (SCPs) are based on electrical activity in the brain usually less than 1Hz. The SCPs are generated by several mechanisms. These include (a) slow graded post-synaptic potentials of the giant pyramidal cells in the cortex (usually going down to around 0.5Hz)- these are usually oscillating signals. (b) The predominant source of SCPs is the glial cells that support and regulate the neurons and are closely related to brain activation and brain stability.
This type of training is based upon the finding that preparatory psychological operations co-occur with slow negative fluctuations recorded from the cortex, most prominently at the vertex (Cz). The fluctuations are controlled by Contingent Negative Variations. The contingent negative variation (CNV) is a long-latency electroencephalography (EEG) surface negative potential with cognitive and motor components, observed during response anticipation. CNV is an index of cortical arousal during orienting and attention. The generation of CNV relies on the activity of a thalamo-cortical-striatal circuit encompassing the prefrontal cortex, primary and supplementary motor areas, posterior parietal cortex, anterior cingulate cortex (ACC) and thalamic nuclei. The late CNV mainly appeared to be associated with activations in the frontal cortex, dorsal ACC and thalamus and increased activity in midbrain dopaminergic nuclei (very likely corresponding to the substantia nigra). The initial CNV was localized mainly in motor and premotor cortical areas and the caudate nucleus.
Negativation: Training the Cz slow potential towards negativity is associated with activation of the cortex. That is, there will be increased firing in the cortex neurons due to long-lasting depolarisation of apical dendrites. It is thought that training in SCP may be able to lower the threshold for an action potential by making the threshold more negative.
Negative SCPs are assumed to reflect lowered thresholds for the excitation of underlying neuronal structures, leading to facilitation of processing e.g., during states of behavioral or cognitive preparation.
Positivation: Training the Cz potential towards positivity (positivation) will inhibit corresponding cortical areas. It is thought that training in SCP may be able to increase the threshold for an action potential by making the threshold more positive, hence needing a larger level of depolarisation in order to create an action potential. In people with seizure disorders you can train them in positiviation in order for them to lower their seizures by increasing the threshold for seizures to occur.
Positive SCPs indicate reduction of cortical excitation of the underlying neural structures (e.g., during behavioral inhibition).
Regulation of SCPs appears to be attenuated in children with ADHD, as indicated by a reduced CNV during attention tasks. That is, people with ADHD do not have the same levels of increased negotiation when preparing for an action. This is also seen in ERPS, with people with ADHd having smaller amplitudes and longer latencies. SCP training increases regulation of cortical excitability in terms of an enhanced post-treatment CNV and reduces ADHD symptomatology. Concerning children with ADHD, a more pronounced CNV seems to predict better outcome of a SCP training.
In this protocol people learn to voluntarily generate negative and positive shifts of potential recorded at Cz. Eye movement artefacts are removed by sensors places next to and under an eye.
Feedback is not continuous like frequency training, but rather occurs in discrete trials. There is a baseline phase (around 2 seconds), an active phase and a reinforcement phase. Feedback is very simple. During the active phase the participant is asked to change potential in a cued direction: up for activation (negativation) or down for relaxation (positivation). A visual reward is given if the cued brain state is achieved. The positivation and negativation trails are randomly presented, and 40 trials is a standard run. A session can last from 2-4 runs. After some training has occurred, the practitioner will then introduce transfer trials. This can happen as early as the third session. During these trials there is no immediate feedback, however there is a reward at the end of the trial so the patient knows whether they managed to perform the trial correctly. This way the patient can learn to perform the skill without immediate feedback, which is important for being able to perform these skills in the real word. Patients can be given the cues used during the training to perform positivation or negativiation so that they can practice in their home or work/school environment.
In a study by Strehl and colleagues they showed that over 50% of patients had over 50% less seizures after SCP training. In a 10 year follow-up self-regulation was still sustained and seizure frequency was low (2014).
The current protocol is standardised in regards to training site and protocol, which makes SCP one of the simplest types of NF to learn and administer. It does however make it one of the least flexible systems, making it limited currently to only certain disorders (ADHD and epilepsy), which makes it off-putting for NF practitioners who wish to purchase equipment that has more flexibility and more wide spread use. The system is reliant upon an AC amplifier rather than the DC amplifiers used in frequency training, which makes the costs somewhat prohibitive to most NF practitioners working in the field. For this reason SCP is not particularly wide spread in Australia, mostly confined to Europe and large institutions. The costs of some equipment can be in the vicinity of $20,000 making this type of NF out of the league of standard Australian practitioners who in general prefer the flexibility and the broader training scope that top class frequency systems can supply at around 1/3 of the cost. Whilst SCP is promising in regards to its early research, it hasn’t taken off in Australia with practitioners and is only likely to when the research has been able to demonstrate any applications other than ADHD, such as mood disorders, autism spectrum and other areas where frequency training is starting to demonstrate strong findings. So far SCP has no demonstrated advantaged over the commonly used frequency training and the future of NF looks like it will be based in the newer more exciting Z-score training and LORETA which are purporting to cut down training times dramatically and be even more precise in modulating specific pathways than frequency training.