Lecture 8: Brain-computer interfaces, neurofeedback and neuronal oscillations and synchrony Flashcards
What are brain-computer interfaces?
Brain steering computers or computers steering brains
What are negative slow cortical potentials (SCPs) and what do they cause?
They reflect depolarization of cortical cell assemblies that reduces their excitation threshold (i.e. increase excitation). They arise from non-specific thalamic input that has cortico-cortico projections. They are called negative slow cortical potentials, because when the superficial layers of the apical dendrites are activated, it creates a negative charge around the cortex. The electrode on top will measure a slow negative deflection.
What role do SCPs have?
They are believed to be involved in attentional mechanisms.
What is attention (in regard to brain processes)?
The brain making certain brain regions more susceptible for processing incoming stimuli.
Just know that since we can regulate our attention, we can also self-regulate SCPs (mental control).
Like in this picture. Where we make use of our attention to generate SCPs to move an object.
What is the P300 event-related potential?
It is elicited by infrequent task-relevant stimuli. This is a stimulus that is generated when a deviant letter is found during presentation of the same letters in a row. It catches your eye and causes a event-related potential. It’s called P300, P for positive and 300, because it happens around 300 ms.
So what does the amplitude and latency tell you about the P300? What scalp topography does P300 have?
The amplitude tells you the amount of attention devoted to a task. The latency is the stimulus classification speed. It has a parietal topography.
How does the P300 BCI speller work?
The P300 does not only get activated when you notice a deviant stimulus, it can also be used to notice a target stimulus. So if you have the alphabet displayed in front of you, you can highlight rows and colomns to find the target letter. There will be a P300 in the row and colomn where the letter is located.
What are the steps in the P300 speller (BCI cycle)?
- Measurement (EEG, fMRI)
- Pre-processing (frequency filtering)
- Feature extraction i.e. enhancing the signal (spatial filtering, averaging)
- Prediction (is P300 present?)
- Output (write letter)
- Stimulation (continue flashing).
…Cycle continues…
What is an alternative BCI signature?
The sensorimotor rhythm (SMR) through presentation of imagery. (Patients can quickly pick up on and learn this technique).
What is the sensorimotor rhythm?
These are brain waves that arise when the corresponding sensorimotor areas are not active, mostly large alpha activity. SMR decreases in amplitude (beta and gamma) when the corresponding sensory or motor areas are activated, e.g. during motor tasks and even during motor imagery (e.g. thinking about moving).
True/false: BCI works on endogenous and stimulus-evoked EEG
True
On what does BCI work particularly well?
On attention-sensitive EEG signatures (SCPs, P300, oscillations).
Why are conventional drugs having difficult times?
- Expensive to develop
- Side effects are common
- Regulatory procedures tightened
- Effects often negligibly better than placebo or existing drugs.
What is the purpose of EEG-biofeedback?
To give the brain real-time information about its own activity, thereby allowing it to adjust or regulate this activity in a desired direction.
How can biofeedback be used for epilepsy?
So if SCPs are under voluntary control, then you may be able to self-regulate excitability of the cortex. Epileptic patients may be able to stop an arising epileptic attack by self-regulating their excitability of the cortex. See the picture, where epileptic patients actually succeed in discriminating between positive and negative SCPs.
Think of what you can see in this picture.
Here you can see that the red bars show that both the children receiving Ritalin and those receiving Ritalin + EEG-neurofeedback (on reducing the theta activity) improved their behavioral scores on inattention and impulsivity tests, the green bars show that when Ritalin treatment is stopped for a week (“control” ADHD children), attention problems return to their baseline value, whereas those children receiving EEG-neurofeedback retained their good attention scores.
What is an arousal index from sleep-onset EEG?
If you take the ratio of alpha and theta waves from each other, you get an arousal index.
What was used to use a short and long time-scale on the arousal index and to determine if subjects were in a high or low arousal state?
By coupling with two features of sound.
- Volume, which was fluctuating on the short time-scale.
- Perception of sound (the more you sleep in, the more it looks like the sound is further away). Important for long time-scale.
Just note that during the sleep experiment you easily get distracted by your own results (being motivated on the second day to go to sleep, noticing your arousal going down, etc. are all things that can increase arousal).
Ok
So how is the binding problem solved?
When a stimulus arrives to the receptive field of the neuron it starts firing in the gamma frequency band. When this is done by moving a light over the receptive field of a neuron, the neurons in the primary visual cortex will fire repetitively in the gamma frequency band. However, if light bars move in opposite direction over the receptive fields of two neurons, these neurons do not synchronize (bottom figure).
What did the researcher notice when performing this experiment?
When people didn’t noticed the dog, there was no gamma activity. When people noticed the dog, there was gamma activity present.
What did they see in Schizophrenia patients?
That these patients miss a molecular mechanism that is important in establishing long-range synchrony.
