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2011.4.12. YOON, HEENAM 12. General Clinical Issues Relevant to Brain-Computer Interfaces Your slogan 1. Introduction 2. Contents Definition and Essential Features 3. General Clinical Considerations of BCI 4. Current BCI Platforms 5. Conclusion Your slogan 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 Your slogan 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 Your slogan Introduction 6. Environment - Improved insight into the electro-physiological principles - Development of computer processing - Growing social awareness of the needs of the severely handicapped Your slogan 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 Your slogan 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 Your slogan 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 Your slogan 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 Your slogan Definition and Essential Features 2. Essential elements for BCI - Signal acquisition Signal processing Device output Operating protocol Feedback Your slogan 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 Your slogan Definition and Essential Features - Other types · MEG, fMRI, PET -> Costs, slow time constants Your slogan 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 Your slogan 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 Your slogan 1. 2. 3. 4. 5. 6. General Clinical Considerations of BCI Safety Durability Reliability Complexity Suitability Efficacy Your slogan 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 Your slogan 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 Your slogan 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↑ Your slogan 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 Your slogan 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 Your slogan 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 Your slogan 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 Your slogan (1) Sensorimotor Cortex Rhythms 1) mu rhythm - 8~12Hz Not being involved with motor planning or action “rest” activity Produced by thalamocortical circuits Your slogan 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 Your slogan Current BCI Platforms (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 Your slogan 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 Your slogan 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 ↓ Your slogan 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 Your slogan Current BCI Platforms (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 Your slogan (6) Why High Frequency? - Use of power of signal Current BCI Platfo Your slogan 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 Your slogan Current BCI Platforms (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 Your slogan Current BCI Platforms (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 Your slogan 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 Your slogan Current BCI Platforms 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 Your slogan Current BCI Platforms (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 Video Your slogan Current BCI Platforms (6) Life span of microelectrodes↓ - Need of regular replacement Your slogan Current BCI Platforms Your slogan 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