Brain-Computer Interfaces

Question 1

Define neural engineering and give two examples

Answer 1

Electrical interventions in the nervous system and intervenes at the level of the action potential.

Cochlear Implants and Retinal Prosthetics are two examples.

Question 2

What is a way that deep brain stimulation can be use?

Answer 2

It cam be implanted to stimulate the basal ganglia and treat dystonia and Parkinson’s Disease.

Question 3

What is dystonia and how does DBS help?

Answer 3

Dystonia is uncontrollable shaking and difficulty controlling extremities. DBS to the basal ganglia makes limbs more controllable and greatly reduces shaking.

Question 4

DBS

Answer 4

Deep brain stimulation

Question 5

BCI

Answer 5

Brain-Computer Interface

Question 6

Degrees of freedom problem in motor control

Answer 6

Also known as the motor equivalence problem, this is the problem of there being many ways for motor control to achieve a goal.

Question 7

Why is reaching difficult?

Answer 7

It takes years to learn.

Redundant degrees of freedom.

Muscles are complex – the same input can yield different responses depending on the muscle’s position, velocity, and force.

Spinal reflexes and hierarchical control (there are many aspects working in parallel)

Inputs and outputs are in different formats (visual-motor)

Preplanning is necessary

Question 8

Why is preplanning motor movement necessary?

Answer 8

Relying on feedback is too slow.

Question 9

What types of factors go into hand movement?

Answer 9

Join angles, Joint velocity, Join Acceleration, Hand velocity

Question 10

Define velocity

Answer 10

The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time.

Question 11

How does reach differ in joint coordinates versus visual coordinates

Answer 11

In visual coordinates the hand moves straight, but it’s more complex in joint coordinates.

Question 12

What is Fitts’s Law?

Answer 12

A predictive model of human movement primarily used in human–computer interaction and ergonomics. This scientific law predicts that the time required to rapidly move to a target area is a function of the ratio between the distance to the target and the width of the target.

ie. A smaller target farther away is harder to reach.

Question 13

What is the 2/3 power law?

Answer 13

Speed is related to curvature. Is use in talking about handwriting. Links curvature trajectory to angular velocity.

Sounds to me like it’s saying that 2/3 power law says that handwriting is related to the speed of the curve of the hand to the velocity of the angular direction in relation to that.

2/3 is an exponent

Question 14

Scale and effector invariance

Answer 14

These do not change with different body parts. My toes have the same hallmarks as my hands for writing.

effector: an organ or cell that acts in response to a stimulus. (So these do not change if I’m writing with my toes???)

Both are multiplied by a common factor to get the invariance

Question 15

Define effector

Answer 15

an organ or cell that acts in response to a stimulus.

Question 16

What are some regularities of movement?

Answer 16

Fitts's Law
2/3 power law
scale and effector invariance
Repeated movements are very similar
Movements are smooth

Question 17

Three theories of motor contorl

Answer 17

Signal-Dependent Noise (Wolpert and Harris)
Optimal Feedback Control (Todorov and Jordan, and Steve Scott)
Internal Models (Masao Ito and many others)

Question 18

What is signal-dependent noise?

Answer 18

Signal-dependent noise determines motor planning

For a given movement duration, the neural command minimizes error or for a given error tolerance, the neural command maximize speed

Question 19

What is a poisson distribution

Answer 19

is a discrete probability distribution that expresses the probability of a given number of events occurring in a fixed interval of time and/or space if these events occur with a known constant rate and independently of the time since the last event.

Think the mail example

Question 20

What are some safe assumptions of signal-dependent noise theory?

Answer 20

You move as quickly, smoothly, and accurately as noise allows.

The goal is to make accurate movements
Neural control signals are Poisson: the noise scales with the signal
Noise accumulates over the duration of the movement

Neurons are also variable in that particular details will change about individual neuron firing each time.

Question 21

Can optimal feedback control theory be falsified?

Answer 21

No

Question 22

What does Optimal Feedback Control theory say?

Answer 22

There must be redundancies because there is multiple input and output.

Redundant noise can be exploited.

You don’t correct error in task performance that don’t hurt you. Also considered a minimal intervention principle for this reason.

Question 23

What are Internal Models?

Answer 23

They are models where the brain creates an internal representation of the body and the environment and uses that to plan movements and to anticipate consequences of actions.

Most of the support for this is in behavioral rather than physiological evidence.

Another way to look at this from wikipedia:
It is a process that simulates the response of the system in order to estimate the outcome of a system disturbance.

The internal model theory of motor control argues that the motor system is controlled by the constant interactions of the “plant” and the “controller.” The plant is the body part being controlled, while the internal model itself is considered part of the controller. Information from the controller, such as information from the central nervous system (CNS), feedback information, and the efference copy, is sent to the plant which moves accordingly.

Question 24

Within the Internal Model, what is the inverse model?

Answer 24

Inverse models use the desired and actual position of the body as inputs to estimate the necessary motor commands which would transform the current position into the desired one. For example, in an arm reaching task, the desired position (or a trajectory of consecutive positions) of the arm is input into the postulated inverse model, and the inverse model generates the motor commands needed to control the arm and bring it into this desired configuration. They are a type of internal model.

Question 25

What is efference copy?

Answer 25

an internal copy of an outflowing (efferent), movement-producing signal generated by the motor system

Question 26

What are forward models?

Answer 26

In their simplest form, forward models take the input of a motor command to the “plant” and output a predicted position of the body. They are a type of internal model.

Question 27

What is a plant?

Answer 27

A body part.

Question 28

What are some non-ideal aspects of muscles?

Answer 28

Force depends on length and velocity. They are sluggish. They only work in one direction (antagonist arrangement)

Question 29

Antagonist arrangement

Answer 29

a muscle whose action counteracts that of another specified muscle. Antagonist and agonist muscles often occur in pairs, called antagonistic pairs. As one muscle contracts, the other relaxes. An example of an antagonistic pair is the biceps and triceps; to contract - the triceps relaxes while the biceps contracts to lift the arm.

Question 30

What is some evidence that M1 codes muscles?

Answer 30

A monkey is trained to rotate a disc to a certain point. Then a weight is added to the disc to make use of muscle extensor or flexor more necessary. This means that the movement is the same, but the engagement of the muscles is different. Neurons increased their rate of firing in response to additional weight. A. Direction-specific increases in single unit activity were observed when there was no load applied to the hand during flexion-extension movements of the wrist. A particular single unit increased its activity for either a flexion or extension movement and was either reduced or quiescent during movement of the opposite direction. This observation alone is consistent with both the “muscle dynamics” and “displacement” hypotheses. B. Regardless of movement direction, the absolute firing rate for a given single unit was variable but predictable given the direction, magnitude, and rate of change of force opposing wrist movement. This observation is consistent only with the muscle dynamics hypothesis.

Question 31

What is one thing that muscle spindles do?

Answer 31

Regulate posture. Seen in myotactic reflext.

Question 32

Myotactic Reflex

Answer 32

The stretch reflex (myotatic reflex) is a muscle contraction in response to stretching within the muscle. It is a monosynaptic reflex which provides automatic regulation of skeletal muscle length. When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases.

Question 33

What is extensor?

Answer 33

Muscle extension.

Question 34

PTN

Answer 34

Pyramidal Tract Neurons

Question 35

What is evidence that M1 codes movements?

Answer 35

Center-Out reach task. Movement is predicted by population vectors.

Question 36

What is the center-out reach task?

Answer 36

The subject has to begin with their hand on something in the center, they receive a target to move to but then must wait for a cue before moving. They get the cue and move their arm to a target outside of the center. This has shown planning, firing of neurons before the beginning of movement.

Question 37

What is evidence that M1 codes for movements and muscles?

Answer 37

The study that determined this looked at extrinsic motion (direction involved in moving the wrist), muscle use (muscles involved in moving the wrist), and joint use (direction of joint change). The monkey held its hand in a pro, sub, or mid position. Then he flexed the wrist in 8 different directions according to a cue on the screen. Also considered was the preferred direction of the muscles involved in that movement and how those preferred directions were reflected in different wrist starting positions. Point being, all of the variables could be measured independently and it was found that they all involve activity in M1. This activity isn't on the same neuron though.

Question 38

Intrinsic movement

Answer 38

This is the type of movement. In other words, flexing my wrist is the same type of movement regardless of my wrist starting position.

Question 39

Extrinsic movement

Answer 39

This is how the body moves through space. In other words, flexing my wrist involves different movements through space depending on my starting point. I can flex and move down or flex and move up.

Question 40

What are three types of neurons identified in the Kakei, Hoffman, Strick paper?

Answer 40

Muscle-like, Extrinsic-like, Extrinsic-like but modulated by posture. These show that M1 codes for muscle and movement.

Question 41

What does PD stand for?

Answer 41

Preferred direction

Question 42

What does the Kakei, Hoffman, Strick paper say about the preferred direction of neurons?

Answer 42

The shifts of neurons parallel those of muscles. (I really don't get this too much).

Question 43

What is the Reference Frame paradigm?

Answer 43

Refers to eye-hand coordination, written here as the eye-to-hand reference frame. Includes visual receptive fields combined with proprioceptive receptive fields. We have to coordinate what we see with where our body is in space. In his words: Visual receptive fields combine with proprioception to yield limb-centered tuning which drives muscles. So goal directed reaching requires a reference frame transformation.

Question 44

What is tuning?

Answer 44

Neuronal tuning refers to the property of brain cells by which they selectively represent a particular type of sensory, association, motor, or cognitive information.

Question 45

What is the hierarchical path for the reference frame transformation?

Answer 45

``` Retina LGN V1 PPC (posterior parietal cortex) PMd (premotor dorsal area) M1 Spine Muscles and then back again ``` This is a feed forward model, taking in the mean firing rate of single neurons (mean because neurons are variable?).

Question 46

What is PPC?

Answer 46

Posterior parietal cortex

Question 47

Problems with M1 codes dynamics?

Answer 47

Doesn't show much that can't be shown through SNR and you have to throw away the mean response. To see the variability you have to take out the mean.

Question 48

What does it mean that M1 codes dynamics?

Answer 48

When I reach for something my path changes and neural firing changes. There's a lot of variability but perhaps a dynamic pattern is visible. For instance variability decreases on stimulus onset. This may allow viewing patterns that escape single neuron recording. What is consistent across neurons (but step one is throw out the mean?)

Question 49

What are BCI algorithms attempting?

Answer 49

To replace the effector

Question 50

What are some parts involved in using a BCI?

Answer 50

Calibration: Scientists move the cursor, record neural activity, and then map what happens in the brain to cursor kinematics. (Observation-based calibration) Control the BCI: Generate the mapped patterns to control the cursor

Question 51

What is kinematics?

Answer 51

the branch of mechanics concerned with the motion of objects without reference to the forces that cause the motion. the features or properties of motion in an object.

Question 52

What are the three decode algorithms?

Answer 52

Population vector Linear Filter Kalman filter

Question 53

What is involved mathematically in population vector algorithms?

Answer 53

1. Fit each neuron with a cosine (gets to vote) 2. Estimate the preferred direct (add up votes) 3. Weight the preferred direction by the cell's firing rate. 4. Sum all the weighted vectors.

Question 54

What can be used to calculate population vectors?

Answer 54

Center-Out Reach task

Question 55

What is a linear filter?

Answer 55

Each spike contributes a little pulse of movement and all of those need to be added together. There's a training matrix algorithm and a testing (decoding) one. I doubt I'll need to know these but they are on the slide. Uses linear algebra Requires finding lots of parameters

Question 56

What is the Kalman filter?

Answer 56

It was invented to track satellites is a continuous Bayes estimator. It has a state equation and an observation equation. It offers uncertainty weighting by adding in noise Also uses known statistics of hand movements. Combines a trajectory model and observation model that can compute each timepoint.

Question 57

What are the known statistics of hand movements?

Answer 57

arm state x^t=[Position, velocity, acceleration] Determined in the center-out reach task Used in Kalman filter

Question 58

What is a problem with BCI?

Answer 58

Calibration is hard to escape. One monkey's neural pattern doesn't apply to another monkey or to the same monkey the next day.

Question 59

Which algorithm is best?

Answer 59

Depends on what you think M1 does. All of the algorithms decode velocity. Many new algorithms are coming out all the time. Plasticity probably erases the differences between them. Amount of experience and implementation details like parameter numbers and quality of recording can skew results. (how you use them matters?)