Neural coding and brain machine interfaces Flashcards
what is a brain machine interface (BMI), the basic science behind BMIs
What is a brain machine interface (BMI)?
A medical device that measures or alters the electrophysiological activity at the level of populations of neurons.
What are the two main types of BMIs discussed?
- BMIs to restore lost sensory abilities
- BMIs to restore lost motor abilities
What is an example of a condition treated by sensory BMIs?
Hearing loss.
Who is a famous historical figure that experienced hearing loss?
Beethoven.
and Helen Keller
What are the two primary causes of hearing loss mentioned?
neural basis
- Damage to sensory hair cells in the cochlea which is a loss of critical steps in the hearing pathway
What is a cochlear implant?
A device that bypasses the ear’s apparatus and electrically stimulates primary auditory afferents.
(stimulates surviving neurons of auditory nerve)
How does a cochlear implant work?
It uses a microphone and circuitry sound analyser (frequency decomposition) and stimulates specific parts of the cochlea with an array of electrodes.
what part fo the ear vibrates from sound
basillar membrane
what does location of maximum vibration in basillar membrane depend on ?
tone frequency
What is frequency decomposition?
The process of breaking down sound into its pure tone components.
What does a spectrogram represent?
A visual representation of the frequency composition of sounds over time.
how sound is a mixture of pure tones/ displays sounds as pure tones
What is the role of the basilar membrane in hearing?
It vibrates in response to sound, with different regions sensitive to different frequencies.
example of a sensory BMI
cochlear ear implant
what part of the ear performs frequency decomposition ?
chochlea
What is the average word recognition performance for cochlear implant users one month after implantation?
Approximately 40%.
What is the average sentence recognition performance for cochlear implant users one month after implantation?
70%
What is a significant advantage of recognizing sentences over individual words for cochlear implant users?
Contextual information helps improve recognition performance.
As of 2011, how many cochlear implants were there worldwide?
Just over 200,000.
most wide spread and successful sensory BMI
What is one type of motor pathology relevant to brain machine interfaces?
Spinal cord injury.
What does a C1 spinal cord injury typically result in?
Loss of function from the neck down
- tetraplegia
- respirator required
what does a C7 spinal cord injury result in
loss of function from chest down
- paraplegia
can still use arms and hands
What is amyotrophic lateral sclerosis (ALS)?
A pathology of motor neurons leading to paralysis and other severe symptoms such as respiratory failure and locked in state
What does the locked-in state refer to?
Complete paralysis of all voluntary muscles, including the ability to express feelings.
legs, hands, eyes !!
What is the first component of a brain machine interface aimed at restoring motor function?
A microelectrode array that measures electrical activity of neurons.
What is the purpose of the decoding algorithm in a BMI for motor function (after electrodes)?
To interpret the intentions of the person, such as movement intentions. This si then passed to a robotic limb or movement of a cursor on a mointor.
Acuator
summary of key BMI coponents for motor function
- electrode array
- decoding algorithm
- actuator
True or False: Cochlear implants work equally well for all users.
False.
What is the first stage of a brain-machine interface?
An electrode array
The electrode array is placed over the motor cortex.
What is the purpose of the decoding algorithm in a brain-machine interface?
To decode the intentions of the person
It attempts to interpret thoughts such as moving eyes or reaching with an arm.
What is an actuator in the context of a brain-machine interface?
A robotic limb or cursor movement
It acts on the environment based on the decoded intentions.
What is the significance of the motor homunculus?
It represents the organization of motor functions in the motor cortex
It illustrates how different body parts are controlled by specific areas of the cortex.
What is the typical voltage range for connections from motor cortical neurons to motor neurons in the spinal cord?
100 to 200 microvolts
This is significantly lower than the approximately 100 times larger signal needed to cause an action potential.
According to Georgiopoulos et al., what drives motor control?
Coordinated activity of neurons in the primary motor cortex
This was demonstrated through experiments with monkeys reaching in various directions.
What is a tuning curve in the context of neuron activity?
A graph showing the relationship between direction of movement and neuron firing rate
It illustrates how specific neurons respond to different movement directions.
How do population vectors relate to motor control?
They represent the integrated directional votes of neurons
Each neuron votes for a direction based on its firing rate.
What was a key finding from the study on monkeys making spiral movements?
Moran & Schwartz (1999)
They could reconstruct complex movements using population vector decoding from motor cortex activity
This implies potential for decoding more intricate movements beyond simple reaches.
What is the Utah Array?
Petersen & DIamond (2000)
A microelectrode array used for recording electrical activity in the brain
It consists of 100 microelectrodes and is useful for brain-machine interfaces.
What was the purpose of the study conducted in 2002 using the Utah Array?
Surruya et al. (2002)
To demonstrate that neural activity can control a cursor
Monkeys used a joystick to move a cursor based on their brain activity / then used neuronal control without joystick
What is neural control in the context of brain-machine interfaces ?
Direct control of a cursor by neuronal activity without a joystick in monkeys/ it is possible to decode movement based on activity in M1
The monkey was able to control the cursor using only its brain signals.
What was the aim of the BrainGate clinical trials?
Hochberg et al. 2006
To develop brain-machine interfaces for individuals with severe motor disorders
- involved implanting microelectrodes
participant MN in ‘Braingate’ trials
- spinal cord injury C3-C4
- complete tetraplegia
- implanted with Utah array in M1 arm area
What was the condition of the participant MN in the BrainGate trial?
Complete tetraplegia due to spinal cord transection
MN could not move arms or legs but could imagine movements.
What did the researchers record from MN during the BrainGate trial?
The activity of neurons in the primary motor cortex during imagined movements
They analyzed how different neurons responded to various imagined directions.
What does a population vector estimate in the context of motor control?
The direction of intended movement based on neuron firing rates
It integrates signals from multiple neurons to predict movement direction.
True or False: A single motor neuron can influence movement on its own.
False
Movement is a result of coordinated activity among multiple neurons.
Fill in the blank: The population vector is computed by scaling the length of neurons’ preferred direction arrows by their _______.
firing rate
What does each row in the primary motor cortex activity represent in the ‘Braingate’ trials?
Imagined movement in a different direction.
Which directions are represented in the primary motor cortex activity?
- East
- North
- West
- South
strengths of Hochberg et al./ Braingate trials
- first demonstration of neural control in human
limitations of Hochberg/ braingate trials
- complexity of movemets was limited
- so how much practical use is there ?
What is the significance of Georgopoulos’ tuning curves?
They illustrate how neurons in the motor cortex are tuned to specific directions of movement.
What did Hochberg et al. train an algorithm to predict?
The direction of imagined movement based on primary motor cortex neuron activity.
What was the performance accuracy of MN in the reaching task?
80 to 90%.
What were the limitations of the Hochberg paper?
- Task simplicity with only four reaching directions (N/S/E/W)
- Limited degrees of freedom in movements
What was the first demonstration accomplished by the Hochberg paper?
Neural control in a human.
Fill in the blank: The complexity of movements in Hochberg’s study was very _______.
limited.
What does the term ‘degrees of freedom’ refer to in the context of movement?
The complexity and variability of possible movements.
What is the significance of spike-trigger averaging in understanding motor control?
It helps determine which muscles are activated by specific motor cortex neurons.
what is dysarthria
difficulty breathing
what is dysphagia
difficulty in eating
