Transcript Current BCI Platforms

2011.4.12. YOON, HEENAM
12. General Clinical
Issues Relevant to
Brain-Computer
Interfaces
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1. Introduction
2.
Contents
Definition and
Essential Features
3. General Clinical
Considerations of BCI
4. Current BCI Platforms
5. Conclusion
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Introduction
1. Emerged Idea
- Machines that can be controlled by one’s thoughts
- Machines that create a new output channel from the
brain beyond the natural motor and hormonal
commands
2. Terms
-
BCI (Brain Computer Interface)
DBI (Direct Brain Interface)
BMI (Brain machine Interface)
Motor Neuroprosthetics
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Introduction
3. Source
- Electrophysiological signal in the brain
4. Purposes
- Communication
- Control something
5. Background
- Improving the quality of life for people with Motor
impairment, including SCI, neuromuscular disorders
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Introduction
6. Environment
- Improved insight into the electro-physiological
principles
- Development of computer processing
- Growing social awareness of the needs of the
severely handicapped
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Introduction
7. Requirement
-
Framework of how these systems operate
The current BCI platforms and limitations
The relevant issues when applied clinically
Milestone for their evolution toward entering
standard clinical practice
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Definition and Essential Features
1. Definition
- A communication system that does not depend on
the brain’s normal output pathways of peripheral
nerves and muscles
(The first International Meeting on Brain Computer
Interface Technology(2000))
- Machine that can decode human intent from brain
signal alone
· Not required the assistance of motor activity
· A BCI allows for a completely novel output pathway
from the brain
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Definition and Essential Features
· BCI changes signals from mere reflections of CNS
activity (EEG rhythms, neuronal firing rate)into the
intended products of that activity
· Two BCI Systems
Input BCI(perception)
Output BCI
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Nerves
Muscles
Movements
Definition and Essential Features
BCI
Electrophysiological
Signal
Hardware
Software
Action
· Feedback
- To improve the performance
- A certain level of training and learning is need for
both for the user and the computer
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Definition and Essential Features
2. Essential elements for BCI
-
Signal acquisition
Signal processing
Device output
Operating protocol
Feedback
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Definition and Essential Features
(1)Signal acquisition
- A measurement of the electrophysiological state of the
brain in real time
- Usually recorded with electrodes(non/invasive)
· EEG: recorded from the scalp
· ECoG: recorded beneath the skull
· Single-Unit: recorded by microelectrodes,
individual neuron action potential firing
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Definition and Essential Features
- Other types
· MEG, fMRI, PET
-> Costs, slow time constants
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Definition and Essential Features
(2) Signal processing
- Feature extraction & Signal translation
· To extract significant identifiable information
from the gross signal
· To render identifiable information into machine
Raw Signal
Statistical
Analysis
Meaningful signal
Hardware
Software
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Definition and Essential Features
(3) Device Output
- Overt command or control functions that are
administrated by the BCI system
(4) Operating protocol
- Important for clinical application
- refers to the method by which the user controls how the
system functions
- Ex. on/off system, controlling what kind of feedback
occurs and how fast it is provided manipulating how
quickly system implements command and switching
between various device outputs
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1.
2.
3.
4.
5.
6.
General Clinical Considerations of BCI
Safety
Durability
Reliability
Complexity
Suitability
Efficacy
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General Clinical Considerations of BCI
1. Safety, Durability, Reliability
- Consideration for risk
· Implant must be reliable and durable in its ability to
acquire signals(DBS, cortical stimulators, grid electrodes)
· Affected by device design
· Patients responds
- Duration problems
· Cause removal and replacement
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General Clinical Considerations of BCI
2. Complexity
There are factors related to performance that must be
deliberated for a BCI to have practical application. These
issues include complexity of control and levels of speed and
accuracy
- Degree of freedom: dimension
->motor impaired individual
· 1DOF: Yes no/Left Right
Limited
· 2DOF: x-axis, y-axis
· 3DOF 3 dimensional movements or 2 dimensions +switch
- For complex movement, more DOF is necessary
->Ex) 7DOF: controlling prosthetic leg
Video
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General Clinical Considerations of BCI
- Speed and accuracy important in real world scenarios
(for minimum error)
· Rate of information communicated per the unit time
· Bit rate↑ -> Accuracy↑
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General Clinical Considerations of BCI
4. Suitability
- Patients with SCI, ALS and so on, require different devices
-
It is vital that the patient population and its underlying
pathology be taken into consideration for what type of
platform maybe used and what function is provides
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General Clinical Considerations of BCI
5. Efficacy
- Example
· 1971s
Degree of control using firing rate of a single neuron
· 1991s
Applied to human BCI
- Need of sufficient research to apply to human BCI
Current BCI Platforms
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 Three types of platforms that have potential for
clinical application in the near future
EEG-Based
ECoG-Based
Single-Unit Based
 Each has technical aspects that give them
dis/advantages regarding their utility in a clinical
setting
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Current BCI Platforms
1. EEG-Based Systems
-
BCI experience has been limited to EEG recordings
Studies have investigated the use of sensorimotor
rhythms, slow cortical potentials and P300 evoked
potentials
Current BCI Platforms
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(1) Sensorimotor Cortex Rhythms
1) mu rhythm
-
8~12Hz
Not being involved with motor planning or action
“rest” activity
Produced by thalamocortical circuits
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Current BCI Platforms
2) beta rhythm
- 18~26Hz
- Normal waking consciousness
· Both real and imagined motor movements are
accompanied by a decrease in mu and beta activity
over sensorimotor cortex
· BCI doesn’t require actual movement but can be
accomplished with imagined movement alone
· Frequency alterations can occur independently of
activity in the brain’s normal output channels of
peripheral nerves and muscles and could therefore
serves as the basis for a BCI
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(2) Slow Cortical Potentials(SCPs)
- Slow changes in EEG potentials centered at the
top of the head, or vertex, and occur over time
scales of several seconds
- Negative SCP: Movement and cognitive functions
involving cortical activation
- Positive SCPs: A reduction in such activations
- Can be learn to control SCP amplitude
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Current BCI Platforms
(3) P300 Evoked Potentials
- When infrequent or significant auditory, visual,
or somatosensory stimuli
- Positive potential in the EEG that peaks at about
300ms
- Centered over parietal cortex
- Depends mainly on whether the user wishes to it
- Application: Word Processing
Video x2
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Current BCI Platforms
(4) Advantages
- EEG-based paradigms are noninvasive
- Users can control devices without a neuromuscular
requirement
(5) Disadvantages
- Artifact problems(Electrodes movement, muscle
movements, electrical environment)
- Signals are distant from the sources
· Spatial specificity↓
prohibition of the complexity
of movements
· Limited frequency detection(~40Hz)
- Prolonged user training time
- Electrodes placed in a cap or fixed to the skin
· Long-term solution ↓
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Current BCI Platforms
3. ECoG-Based Systems
(1) Definition
- A measure of the electrical activity of the brain taken
from beneath the skull
(2) Due to the limited access of subjects, it has not
been studied extensively until recently
(3) Based on previous EEG based BCI and the
associated understanding of sensorimotor rhythms
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(5) Signals are different from EEG
- Much more robust
· Magnitude is five times larger
· Resolution is finer
· Frequency bandwidth is significantly higher
->High frequency bandwidths carry highly specific and
anatomically focal information about cortical
processing
(LF: produced by cortical circuits,
HF: produced by smaller cortical assemblies)
->capacitance of cell membranes of the overlying tissue,
combined with the intrinsic electrical resistance of
skull, constitutes a LPF eliminating HF
->So, HF signals are more prominent when recorded by
sub/epidural electrodes
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(6) Why High Frequency?
- Use of power of signal
Current BCI Platfo
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Current BCI Platforms
(6) Research
1) In 2004
- First use of ECoG in closed-loop control
- Brief training(3~24min) 74~100% success rates in
one-dimensional closed-loop control tasks
- Up to 180Hz reflected the direction of two-dimensional joystick
movements
2) In 2006
- Demonstrated evidence that ECoG control using signal form the
epidural space was also possible
video
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(7) Durability of subdural-based devices
(8)In clinical studies, the use of subdural electrodes as
implants for motor cortex stimulation have been
shown to be stable and effective implants for the
treatment of chronic pain
(9)Long-term subdural electrode monitoring for seizure
identification and abortion has also been shown to
be stable
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(10)Advantages
- Higher spatial resolution
- Better SNR
- Wider frequency range
- Lesser training requirements
- Lower technical difficulty
- Lower clinical risk
- Long-term stability
Current BCI Platforms
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4. Single-Unit Based Systems
(1) Basic Theory
Record of firing rate
(2) History
1)1970s
- Animals could be trained to modulate the activity of a single
neuron in their brains ->one dimensional control
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2)1980s
- Method of decoding three-dimensional hand movement
direction from a population of neurons in primary motor
cortex of nonhuman(Ex. Monkey)
- recording the single-unit activity from 50~200
individual neurons during repeated researching tasks
3) Early 1990s
- Enhanced neural decoding methods
4) Late 1990s
- Real-time recording of multiple single units
5) Early 2000s
- Recording chronic, single-unit action potential from a number
of neurons simultaneously
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(3) Applied to quadriplegic subjects
(4) Limited and preclude making definitive conclusions
(5) Two modality tests
- Use of “neutrophic electrode” (1998) , implanted in 2005
- Use of electrode arrays that simultaneously monitor tens
to a hundred
- cortical motor neurons(Utah Array)->implanted in a
spinal-injured quadriplegic patients
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Current BCI Platforms
(6) Life span of microelectrodes↓
- Need of regular replacement
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Current BCI Platforms
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Conclusion
- The field of neuroprosthetics is in its infancy
- Current research
· Electrical encoding the information in a human’s thoughts
- However it can be used by impaired users to interact
with his/her environment
- Given the rapid progression of technologies, signal
analysis tech, emerging ideas should be achieved
· EEG, ECoG->complexity of control
· Single-unit platform->implant durability
· clinical application