BCI and neuronal basis of EEG

Question 1

what is a brain computer interface

Answer 1

direct communication pathway between a brain and an external device
Overall aim - to assist, augment, or repair cognitive or sensory-motor functions

Question 2

Invasive and non-invasive

Answer 2

Neuroprosthetics: restoring damaged hearing, sight or movement
-Neuroprostetics in primates lead the advances

Question 3

Cochlear implant

Answer 3

A surgically implanted electronic device
-Provides hearing to a deaf person with non-functional hair cells.
-0.5 mill using it worldwide
-Often young children

Question 4

Implantable visual prosthetics for the blind

Answer 4

Implanted in a few tens of patients
Nov 2011- first commercial implant of retinal prothesis

Question 5

Interim summary

Answer 5

The nervous system is electric
-You can read its activity and couple it to external devices
-Stimulate neural tissue to induce sensations of touch, sound or light or normalize pathophysiological activities.

Future developments rely better on:
- understanding of the physiology
- Techniques to measure and stimulate physiological systems
-Analysis and interpretation of physiological signals

Question 6

Why research with EEG

Answer 6

Fundamental knowledge and curiosity: where, when and how?
Consciousness: What’s necessary for conscious perception?
“Free will”: Do we have it or not?
Inexpensive and safe BCI

• The evidence suggests that Gestalt binding in healthy controls is mediated by synchrony of oscillations in beta- and gamma-frequency bands.

Question 7

Future of EEG

Answer 7

Real-time recording
Computerized analysis
Informative interpretations
…coupled with useful interventions

Question 8

Advantages of EEG

Answer 8

-Direct reflection of activity (in contrast to hemodynamic response)
-High temporal resolution (~1 ms): no delay
-Greater specificity?
One voxel in fMRI generates multiple oscillations with distinct functions
-Increasingly portable
-Non-invasive
-Availability
-Inexpensive

Question 9

Abbreviations

Answer 9

ECoG: electrocorticography
LFP: local field potential
EEG: electroencephalography
MEG: magnetoencephalography
fMRI: functional magnetic resonance imaging
PET: positron emission tomography

Question 10

What is a resolution

Answer 10

What is “resolution”?
Ability of a technique to separate two events in space (spatial resolution) or time (temporal resolution).
Or accuracy of localizing an events in space (spatial resolution) or time (temporal resolution).

Question 11

Time space trade off

Answer 11

Some techniques provide high temporal resolution of brain activity, while others provide higher spatial resolution.

Question 12

EEG recording of electrical activity part 1

Answer 12

Neurons are like small batteries: the concentration of ions such as sodium is not the same on the inside and outside of the cell.
Thus, when a neurotransmitter causes the opening of a transmembrane ion channel, a current of ions will flow from the outside to the inside of the cell =>
That causes a transient potential difference around the neuron, and because the head is full of water, which conducts electric fields, electric potentials are propagated to the outside of the head.

Question 13

EEG recording of electrical activity part 2

Answer 13

These potentials are not the same on different places of the head, because the field decays with distance to the electric-dipole source
Thus, by measuring the potential difference with electrodes having good electrical contact with the scalp, we can measure brain activity entirely non-invasively!
Only, because of each neuron producing a very small electric dipole (i.e., separation of positive and negative charge), many neurons (thousands…) need to be active, which can happen either because of some stimulus/task event, or spontaneously.