Brain-computer Interface

Question 1

What 6 methods can be used to study the brain’s structure (anatomy)

Answer 1

• Autopsy
• Histology / Pathology
• Ecography (Ultrasound)
• X-rays
• CT / CAT (Computer Tomography / Computerized Axial Tomography)
• MRI/MRA (Magnetic Resonance Imaging / Magnetic Resonance Angiography)

Question 2

What 9 methods can be used to study the brain’s function?

Answer 2

• fMRI (Functional Magnetic Resonance Imaging)
• PET (Positron Emission Tomography)
• SPECT (Single Photon Emission Computed Tomography)
• OCT (Optical Coherence Tomography)
• NIRS (Near Infrared Spectroscopy)
• EEG (Electroencephalography)
• MEG (Magnetoencephalography)
• ECoG (Electrocorticography)
• Neuronal / Intracortical recordings

Question 3

What is fMRI, how does it work?

Answer 3

Functional Magnetic resonance imaging modified version of MRI which provides information about brain function.
* Oxygenated hemoglobin (HbO) – diamagnetic (slightly repelled by a magnetic field)
* Deoxygenated hemoglobin (HB-) – paramagnetic (slightly attracted by a magnetic
field)
* Blood serves as a natural contrast agent for detecting brain activity.
* Regions of the brain where more neurons are active will consume more oxygen as
compared to regions of the brain where more neurons are inactive.
* BUT, what is detected in fMRI is oxygen supply and oxygen consumption
* Therefore what fMRI detects is the unused blood or the oxygenated hemoglobin,
also known as the Blood Oxygen Level Dependent or BOLD contrast.

Question 4

What is NIRS, how does it work?

Answer 4

Near Infrared Spectroscopy
*Uses light in the near-infrared range (700-1000 nm).
*This light can pass through skin, bone, and other tissues easily.
*Measures oxygen levels in the blood and tissues.
*Oxygenated and deoxygenated hemoglobin absorb this light well.
*Also detects cytochrome oxidase, an enzyme crucial for energy production in cells.

Question 5

What does EEG measure?

Answer 5

EEG (Electroencephalography) measures electrical activity in the brain.
It primarily detects field potentials, which are the summed electrical activity of many neurons.
It does not directly measure action potentials, which are the individual signals of single neurons.

Question 6

What is MEG?

Answer 6

Magnetoencephalography
Method for detecting the very weak magnetic signals generated by neuronal electrical activity.

Question 7

What is the benefit with MEG compared to EEG?

Answer 7

The skull is transparent to magnetic fields
therefore a better spatial resolution can be
obtained with EMG as compared to EEG.

Question 8

What neurons are MEG/EEG more sensitive to?

Answer 8

MEG is only sensitive to neurons
tangentially oriented to the skull surface
while EEG is mostly sensitive to neurons
perpendicularly oriented to the skull
surface.

Question 9

What does EEG pick up/measure?

Answer 9

Gross, macroscopic, coordinated, and synchronized firing mostly of
cortical neurons perpendicularly oriented in relation to the scalp

Question 10

Name 7 variations of electrodes used for EEG

Answer 10

• Self-adhesive AgAgCl surface electrodes
• Ag/AgCl, Z or Steel reusable surface electrodes
• Platinum needles
• Active electrodes
• Dry electrodes
• Epidural Screw Electrodes (ESE)
• Electrode caps

Question 11

What is the placement-system used for EEG measurements called, and why?

Answer 11

10-20, refers to the distances between the electrodes (in %)

Question 12

What are the 3 types of EEG recordings and when are they used?

Answer 12

• Ipsilateral Ear Reference - Investigation of brain activity asymmetries
• Linked Ear Reference - “Global” activity
• Contralateral Ear Reference - For interhemispheric comparison

Question 13

Describe the following (EEG)
Beta, Alpha, Theta, Delta

Answer 13

Beta - Dominant rhythm when alert or anxious or eyes open.
Alpha - Major rhythm in relaxed adults.
Theta - Abnormal in awake adults but perfectly normal in children up to 13 years and during sleep.
Delta - Dominant rhythm in infants up to 1 year and in stages 3 and 4 of sleep

Question 14

What is ECoG, and how does it work?

Answer 14

Electrocorticography

• Electrodes are placed directly onto the
  cortical grey matter.

Question 15

What are the 7 benefits of ECoG in comparison to EEG?

Answer 15

• More effectively recording signals with higher frequencies
• Better SNR (since the skull acts as an attenuator of high-frequency
  signals)
• ECoG electrodes provide higher spatial
  and temporal resolution than EEG
• Wider bandwidth
• Higher amplitude
• Better performance
• Better long-term stability

Question 16

What is a problem with Neuronal / Intracortical recordings

Answer 16

detect and separate spikes
corresponding to different neurons

Question 17

What are the 7 post-processing steps when detecting spikes?

Answer 17

1. Input: Raw Signal
2. Spike Detection
3. Alignment
4. Feature Extraction
5. Dimensionality Reduction
6. Clustering
7. Output: Spike Times

Question 18

Name the 6 things BCI rely on

Answer 18

• Selective attention
• Motor imagery
• Auditory imagery
• Emotional imagery
• Spatial navigation
• Mathematical task imagery

Question 19

Translation algorithms should be…

Answer 19

… as simple as possible

Question 20

What is the drawback of BCI P300 communication?

Answer 20

Drawback: to get a clear P300, 15 or more trials of EEG data is necessary for the averaging –> alow