Sensory-Motor integration Flashcards
What is the brain-machine interface?
• Brain-machine interface: an artificial process that allows the brain to exchange information directly with an external device
What are the three levels of movement control?
o Lowest level- Spinal cord
o Second level- Brain stem
o Highest level- PMC, premotor cortex and SMA
Describe what the lowest level of movement control controls (and what it is controlled by)
o Lowest level- Spinal cord
Neuronal network (spinal cord interneurons) for execution
• Control reflex and voluntary stereotypic behaviours
• Convergence on motor neurons
• Controlled by descending pathways
Contain simple circuits that control simple actions
Describe what the second level of movement control controls
o Second level- Brain stem
Two parallel neuronal systems, medial and lateral for tactics (how movements are going to be done)
• Control of posture, integration of vestibular and visual information
• Control of distal muscles for goal directed movements (rubrospinal tract)
Describe what the highest level of movement control controls and its components
o Highest level- PMC, premotor cortex and SMA
Three cortical areas that connect to spinal cord (corticospinal tract) and to brain stem- for strategy
• Primary motor cortex- execute action
o Provides direct input to the motor neurons and to interneurons
• Premotor cortex- coordinate and plan
• Supplementary motor area- coordinate and plan
How is voluntary movement governed and organised?
- Voluntary movement is governed by conscious planning
* It is organised around performance of a purposeful task
How does voluntary movement performance improve?
• Task performance improves with experience and learning
What initiates voluntary movement?
- Voluntary movement can be initiated internally without a sensory stimulus trigger
- Sensory stimuli do not dictate the resulting movement, although they guide the specified task
What are the two main descending pathways that control motor neurons innervating the skeletal muscle, what is their origin and what do they do?
• Indirect pathway
o Originates in brainstem
o Cortex provides input
o Control of posture; some reflexes
• Direct pathway
o Originates from cerebral cortex
o 90% of the fibres cross to contralateral side at the medulla
o Voluntary movement
What are different types of brain signals that carry information for movement production?
• Changes in neurotransmitter concentration
• Changes in membrane potential (continuous)
• Spiking pattern/profile
• Hemodynamic profile
o Changes in blood flow in specific brain areas
What is the best type of brain signal for movement production available for reading the code? Why?
• Spiking pattern/profile- best candidate to give measurement for coding motor events
o Spikes can provide local information and precise information about the timing of the activation of the neurons
How is spiking pattern/profile best measured for reading motor code and why? How does this measuring processes work?
Local field potential (electric potential in the extracellular space around neurons- reflects changes in synaptic activity) and multi-unit activity (spiking profiles of multiple neurons) could be best measurement for coding motor events because of their temporal course
• Multi-unit activity measurement:
o Electrophysiological signals recorded with extracellular electrodes are spatially restricted but have good temporal resolution
Take raw microelectrode signal and filter it to extract action potentials
Electrode picks up signal from multiple neurons (evident due to differing amplitude of neuronal recording)
Further filter high frequencies to extract low frequency local field potential (micro EEG)
Why are electroencephalograms a promising but unsuitable method for motor code measurement?
Electroencephalograms could provide access to most cortical areas, but temporal and spatial resolution are relatively poor (coarse type of recording)
What is the key to being able to interpret measures of neural activity that have a large spatial spread and why? What is the consequence of this?
o Local homogeneity is key to being able to interpret measures of neural activity that have a large spatial spread
By recording from individual neurons in a column, information about the selectivity properties of all the neurons in that column can be obtained
If record from many different columns, can potentially rebuild properties of the whole cortex
What does local homogeneity mean?
Local homogeneity means that particular area of the cortex contains neurons that have similar selectivity properties
• Columnar organisation of neurons
How is movement direction recorded in the brain?
- Movement direction is encoded by populations of neurons rather than by single cells
- Population vector seems to have tight correlation with direction of movement
What is a population vector?
o Population vector- vector sum of every cell in the population
How is information in sensory and motor systems frequently encoded and what suggested this?
• Information in sensory and motor systems is frequently encoded in tuning curves
o Single unit recordings from motor cortex suggests that these neurons are organized according to their preferred directions
Whilst preferred orientation will give the strongest response for a neuron, neurons can also respond to other certain orientations but will give weaker responses
Describe the findings of Fritsch and Hitzig (1870)
• Fritsch and Hitzig (1870)-
o Electrical stimulation of primary motor cortex produced contraction of contralateral muscles
o Somatotopic mapping
Describe the input, output and function of the supplementary motor area and premotor cortex
• Supplementary motor area and premotor cortex
o Input: prefrontal cortex
o Receive sensory information from: parietal, temporal
o Efferent: primary motor cortex
o Function: planning of movement
Describe the input, output and function of the primary motor cortex
• Primary motor cortex
o Input: supplementary motor area, premotor cortex, frontal association cortex
o Function: fine motor control
o Neurons in the primary motor cortex (M1) carry information about various aspects of movement, including force, distance and direction
Individual M1 neurons are broadly tuned to the direction of movement
• Increase/inhibition of firing rate depending on movement direction
How can prosthetic devices restore movement after SCI and what is the foundation of knowledge essential for the production of these devices? Describe
• Restoration of movement after SCI
o Implantation with multi-electrode arrays in area of the brain that controls restricted movement
Contains 100 electrodes
• 10x10
Each electrode is separated by 400 microns
1 mm long
o Works as neurons in the pre-motor cortex, primary motor cortex and supplementary motor cortex activated when the patient plans the movement irrespectively of whether the movement is executed or not
On this, patient is trained to think about particular types of movement so researchers can look at the activity of the different neurons and establish a correlation between the intention of the movement and the neuronal activity that can be recorded by the electrodes
• Establishment of code
Describe a brain-spine interface device and the advantage of such a device
• Correlation and conversion of online neural decoding of extension and flexion with an electrical stimulator that controlled contraction of muscles
• Advantages:
o Allows free movement with no restrictions and no cables attached
• Brain/spine interface can restore locomotion of the paralysed limb of the subject
Describe the stimulus-behaviour pathway
• Stimulus (environment)—> change in membrane potential (sensory receptors) -> action potentials (neural pathways)-> perception (cerebral cortex)-> behaviour (organism)