Motor Cortex Flashcards
what is the motor cortex, how it is organized, functional organization, population coding
functions of the brain stem+ summary of brainstem pathways
- posture
- locomotion
- reaching & grasping
even if corticospinal tract pathway severed they still perform these functions, must be brainstem pathways controlling them
functions of the brainstem in the head and neck
- eye movements: vestibular reflexes and orienting
- orofacial behaviours/ rhythms: breathing, swallowing, licking, whisking (animals) etc.
What is the role of the brain stem in motor control?
The brain stem plays an important role in motor control, particularly in posture, locomotion, and reaching and grasping.
What happens if the connection from the cerebral cortex to the spinal cord is severed?
Monkeys are still able to sit up, run across a room, and climb up a cage, indicating that motor behavior can be driven by brain stem pathways.
Why are brain stem strokes considered more dangerous than cerebral cortex strokes?
Brain stem strokes can be fatal because they affect circuits that control essential functions such as breathing and heart rhythms.
What are some examples of rhythms controlled by the brain stem?
- Breathing * Chewing * Licking * Sucking * Whisking
What is the difference between the reflex model and the central pattern generator model?
The reflex model is a chain of motor commands triggered by sensory input, while the central pattern generator generates rhythmic activity internally.
How can we test if a behavior is controlled by a central pattern generator?
By interrupting sensory input; if the behavior continues, it suggests the presence of a central pattern generator.
What did researchers observe when they cut the sensory nerve in the whisking system?
The whisking rhythm persisted even in the absence of sensory input, indicating it is controlled by a central pattern generator.
Where is the central pattern generator for whisking likely located?
In the brain stem, specifically in the vibrissa intermediate reticular formation.
as whisking persists after frontal cortex lesion
where are the facial nerves
… that control whisking
nucleus of 7th cranial nerve
What technique is used to locate the inputs to the facial nucleus?
Retrograde tracing is used to locate the presynaptic neurons / pre-motor neurons that project to the facial nucleus/ cranial nerve nucleus.
what is the candiate CPG for whisking
Vibrissa Intermediate Reticular Formation (vIRt)
as project to facial nerve nucleus
What does electrophysiological recording from the VIRT show during whisking?
It shows rhythmic electrical activity, supporting the idea that the VIRT is involved in generating the whisking rhythm.
What happens when glutamate is injected into the VIRT?
It elicits a whisking rhythm, indicating that the VIRT can produce whisking.
as glutamate agonist (kinate) would inhibit activity
What occurs when the VIRT is lesioned?
lesioned with electrical stimulus on one stide
The whisking rhythm stops, demonstrating that the VIRT is necessary for whisking.
stops on side it is lesioned
summary of brainstem
contains premotor CPG circuits that project to LMNs in spinal cord and brainstem which is how we can produce patterns of behaviour
What are the three types of movement defined in relation to the motor cortex?
- reflexes
- rhythms
- voluntary movements
What characterizes reflexes?
Reflexes are stereotype responses to specific stimuli and are automatic.
How can rhythms be controlled?
Rhythms can be controlled voluntarily to some extent, such as choosing to stop breathing temporarily, but are largely autonomous
What defines voluntary movements?
Voluntary movements are intentional, involve choices, and are learnable.
conscious
What are the two parts of the motor cortex?
- Primary motor cortex
- premotor cortex
Where are the primary motor cortex and pre-motor cortex located?
In the posterior part of the frontal lobe.
What is cytoarchitecture?
Cytoarchitecture refers to the cellular morphology and staining characteristics of different parts of the cerebral cortex.
nissl stain and brodmann area
Where is the primary somatosensory area located?
In the posterior part of the frontal lobe
What does cytoarchitecture refer to?
Staining for cellular morphology
Who discovered that different parts of the cerebral cortex stain in characteristic ways?
Brodmann
What is area 3B known for?
It is the primary somatosensory area (S1), the touch area
What is area four known as?
Primary motor cortex
What distinguishes layer four in primary sensory areas like area 3B?
The presence of a granular layer
What is a characteristic feature of primary motor cortex regarding layer four?
The absence of a granular layer / AGRANGULAR
What was discovered in 1870 about the motor cortex?
Electrical stimulation (of frontal lobe) (motor cortex and premoto cortex) could elicit somatotopically organised movements
What does somatotopically organized movements refer to?
Movements that are organized according to body regions
where is M1/ primary motor cortex located
(Broadmann area 4)
precentral gyrus
What technique did Sherrington and colleagues use to study the motor cortex?
Electrical stimulation of the cortex
What did the stimulation of different locations in the motor cortex (area 4) reveal?
A map of body musculature across the surface of the brain
What hypothesis arose from the mapping of the primary motor cortex?
Primary motor cortex should be considered as a muscle map
- similar to Penfield S1 homunculus map
What is the neuron doctrine associated with?
Ramon y Cajal’s discovery that the nervous system is composed of discrete individual cells called neurons
What are the two predictions of the muscle map hypothesis or M1 function?
- Each muscle should be represented in one location of primary motor cortex
- Each M1 neuron should activate precisely one muscle
What did the micro-stimulation experiments reveal about muscle representation in M1?
same muscle contracts in response to stimultion over large region of M1/ One muscle is represented over a wide expanse of primary motor cortex so inconsistent with prediction that each muscle should be represented in one location in M1
What technique is used to measure the electrical activity of muscles?
EMG (electromyography)
What does spike-triggered averaging help identify?
The muscles controlled by a given M1 neuron
What was the result of measuring the activity of a neuron in M1 during a task using EMG?
The neuron was found to control multiple muscles, inconsistent with hypothesis that each M1 neuron should activate one muscle
so M1 is not a precise muscle map
What does Graziano’s hypothesis suggest about the primary motor cortex?
It should be considered an ethological action map rather than a precise muscle map
What kind of behaviors did Graziano’s longer duration microstimulations in M1 produce?
Coordinated behaviors
What is an example of a coordinated action elicited by M1 stimulation?
Hand to mouth action
and defensive action
Why can’t a single neuron control an individual muscle?
The strength of connections from a motor cortex neuron to a spinal cord motor neuron is insufficient to generate an action potential
connections around 100-200 uV
What does the concept ‘neurons do not walk alone’ imply?
Neurons function cooperatively rather than individually
What classic experiment sheds light on how neurons function together?
Georgopoulos et al.’s experiment with monkey’s
What phenomenon do neurons exhibit when firing action potentials?
Cooperative phenomenon
In the experiment by Georgopoulos et al., what task were monkeys trained to perform?
Make reaching movements
What area of the brain was monitored during the monkey reaching movements?
Primary motor cortex (M1)
What was observed about the firing rates of neurons in relation to reaching directions?
Different reach directions were associated with different rates of action potential production/ M1 neurons are ‘tuned’ to reach direction
What is a tuning curve?
A plot showing the average firing rate of a neuron as a function of reach direction
What is the issue with tuning curves when explaining precise reaching movements?
They are very broad, making it difficult to understand how monkeys achieve precise movements
What concept did Georgopoulos propose to explain how neurons function collectively?
Population coding
what is population coding
M1 neurons operate together to control movement
What does the population vector hypothesis state?
- each M1 neuron has a PREFFERED DIRECTION (PD) of reaching
What is a preferred direction of a neuron?
The reaching direction that elicits maximal firing rate in that neuron
How are preferred directions of neurons represented in the population vector hypothesis?
As vectors on a diagram
- vectors result from multiplying each neuron’s PD vector by its firing strength
What does the strength of a neuron’s vote for a reaching direction depend on?
The neuron’s firing rate
What does the red arrow represent in the population vector hypothesis?
The population vector, which predicts the direction of the monkey’s reach
implication of population vector hypothesis
each direction is encoded by M1 population vector
How accurately can the population vector predict a monkey’s reach direction?
There is a remarkably tight match between the predicted direction/ population vector and the actual reach direction
conclusions from population coding
- can explain how precise reaching is possible even though individual neurons are less precise
- accurate prediction of behaiour from neural activity
What are the implications of being able to predict behavior from neuronal activity?
Insights into brain function and potential applications for prosthetic limbs
What is the role of motor cortex in voluntary movements?
Neurons control voluntary movements as a population, neurons do not control muscles individually
Fill in the blank: Each neuron has a characteristic _______ function.
tuning
What does it mean for neurons to ‘vote’ in the context of reaching movements?
Neurons fire action potentials to indicate their preferred direction of movement
What allows researchers to predict movements in paralyzed individuals?
Recording the activity of their neurons in motor cortex
True or False: Neurons can fire action potentials even when a person cannot physically move.
True
