Voluntary Movement and Motor Cortex Flashcards

Flashcards based on the lecture notes about Voluntary Movement and Motor Cortex.

What are voluntary movements?

Consciously willed behaviors that involve the cerebral cortex.

What enables the recording of hundreds of neurons simultaneously in animals performing complex tasks?

Advances in methods and the manipulation of specific types of neurons through genetic targeting.

Name examples of awe-inspiring behaviors that require complex coordination among millions of neurons.

Concert pianist, prima donna ballerina, professional basketball player, or opera singer.

What is the general organization of motor nuclei in the cervical spinal cord?

Hand muscle motor nuclei are located most laterally, trunk muscle nuclei are medial.

Where do the origins of descending pathways underlying voluntary movements arise from?

Cortical areas on either side of the central sulcus and the brainstem.

Name the main regions in the brainstem that are the origin of descending pathways.

The reticular formation and the vestibular nuclei.

What is the medial pathway involved in?

Maintaining upright posture and balance.

What brainstem nuclei represent the origins of the medial pathway?

Vestibular nuclei and reticular formation.

What is the lateral pathway?

A descending motor pathway originating from layer 5 neurons in several cortical regions.

From which cortical regions does the lateral pathway originate?

Primary motor cortex, premotor area, primary somatosensory cortex, and area 5.

What is the pyramidal tract (corticospinal pathway)?

Bundled axons from cortical regions on the ventral side of the medulla oblongata.

What percentage of axons in the pyramidal tract cross over to the opposite side of the spinal cord?

Approximately 90%.

Where does the lateral pathway descend in the spinal cord?

In the lateral column.

Where do axons of the lateral pathway terminate?

Lateral part of the ventral horn and in the more intermediate and dorsal regions of the spinal cord.

What do corticospinal projections from the somatosensory cortex do?

Suppress reflexes that would interfere with voluntary movements.

What deficits were observed in monkeys with lesions to the medial pathway?

Severe postural deficits, inability to sit upright, impaired proximal limb movements, and disability in locomotion.

What abilities were observed in monkeys with lesions to the lateral pathway?

Ability to sit with the head up, stand, walk, run, and climb, but inability to use extremities independently.

What is the rubrospinal pathway?

A descending pathway arising in the red nucleus of the midbrain that has features of both the medial and lateral pathways.

What is the main contributor to the lateral pathway?

Axons arising in the primary motor cortex (M1).

What movements were evoked at different sites along M1 in the anesthetized gorilla?

Movements of the leg, arm, hand, and face/mouth/tongue.

What area is rostral to the primary motor cortex?

Premotor area (Brodmann’s area 6)

Define motor homunculus.

Representation of the motor cortex as one in which separate regions are dedicated to controlling different parts of the body.

What did Leyton and Sherrington report regarding the responses to stimulation of M1 in anesthetized animals?

The responses were highly labile, with functional instability not readily accounted for in a homuncular representation.

What was a striking incompatibility with the concept of the motor homunculus found in Penfield and Boldrey's 1937 publication?

The region of M1 from which finger movements could be evoked almost perfectly overlaps the region from which movements of the shoulder, elbow, and wrist were elicited.

What evidence exists against a strictly homuncular view of the motor cortex?

Studies using trans-synaptic labeling of neurons with rabies virus.

What did Rathelot and Strick find regarding infected cortical neurons in layer 5 of M1?

Infected cortical neurons were distributed over a wide expanse of M1, with neurons controlling individual muscles practically spread over the entirety of the arm/hand region.

What is the complex output organization of the primary motor cortex?

Individual corticospinal neurons supplying a particular motor nucleus can be distributed over a wide expanse of M1 and intermingled with neurons supplying other muscles.

What is a 'many (locations)-to-one' organization in M1?

Corticospinal neurons from many different sites in M1 converging upon a single motor nucleus.

What is a 'one-to-many' arrangement in M1?

Single corticospinal neurons can project to multiple motor nuclei.

What is the main contributor to the lateral pathway, and where does it originate?

Axons arising in the primary motor cortex (M1, Brodmann’s area 4) just rostral to the central sulcus.

What did Wood Jones observe regarding activation of the extensor carpi ulnaris (ECU) muscle?

When extending the thumb by the actions of the extensor pollicis brevis (EPB) muscle, there is robust, synchronized activation of the ECU.

What does the spiking activity of individual neurons in M1 correspond to in terms of movement?

Muscle activity or more abstract features of a motor behavior, such as movement direction.

What did Evarts conclude about the firing rates of pyramidal tract neurons in M1?

They code for the intensity of muscle contraction (and associated muscle force) needed to perform various tasks.

What is one prescient issue addressed by Evarts?

Whether M1 neural activity is directly associated with muscle activity or related to more abstract features such as movement direction

What question did Shen and Alexander address in their experiment?

Whether primary motor cortex is responsible for representing desired movements rather than muscle activities needed to make the movements.

What did Shen and Alexander find regarding M1 neurons and movement direction?

Over half of the M1 neurons seemed to encode movement direction of the task-relevant effector and not which muscles or limb movements were involved.

Describe the complexity of the motor cortex.

Millions of neurons, each receiving on the order of ten thousand synaptic contacts from other neurons, and each neuron sending connections to hundreds of other neurons.

What is the main output entity of the motor cortex?

Layer 5 corticospinal neurons.

How do artificial neural networks perform highly complex tasks?

By having the network attempt to perform a desired task and then compare what was produced to what was intended, adjusting synaptic strengths based on the error.

What is an early attempt to consider neural populations as a whole?

Donald Humphrey and colleagues recorded activities from several M1 neurons simultaneously and combined their firing rates to predict movement parameters.

What is a raster plot?

A plot displaying spike times for repeated trials of the same behavior or sensory input, aligned to a particular event, and then stacked above one another.

What is a peri-stimulus time histogram (PSTH)?

A histogram showing the response of a neuron around the time that the stimulus was presented or behavior instigated.

What is the preferred direction (PD) of movement for a neuron?

The movement direction associated with peak firing rate based on a sinusoidal curve fitted to the neuron's firing rates for each movement direction.

What is population vector analysis?

Represents the activity of each neuron as a vector pointing in the neuron's preferred direction, with the length scaled based on how close the PD is to the impending movement direction.

What is a population vector (pv)?

The vector sum of all individual neuron vectors, representing the overall direction that the movement will follow.

How can population vectors be computed on finer time scales?

In successive time windows during a reach, producing an array of population vectors.

What are brain-machine interfaces (BMIs)?

Devices that use activity recorded from many neurons to predict intended behavior and control external devices.

Name two main pathways that convey commands from the brain to spinal machinery.

The medial pathway and the lateral or corticospinal pathway.

What do layer 5 (corticospinal) neurons encode?

The intensity of muscle activation.

What do M1 neurons represent?

Complex and abstract features of desired movements.