week 9 action

Question 1

The Anatomy and Control of Motor Structures

Answer 1

see slide 5 for image:

premotor and supplementary motor cortex regions > motor cortex > brainstem > spinal cord > output to muscles

premotor and supplementary motor cortex regions > basal ganglia > either back to pmsmcr or on to > motor cortex >< brainstem > spinal cord > output to muscles

premotor and supplementary motor cortex regions > cerebellum > back to pmsmcr or on to > MC > BS > SC > output to muscles

Question 2

Overview of the motor pathways.

Answer 2

Note hierarchical structure

All connections to the arms and legs originate in the spinal cord. The spinal signals are influenced by inputs from the brainstem and various cortical regions, whose activity in turn is modulated by the cerebellum and basal ganglia. Thus control is distributed across various levels of a control hierarchy. Sensory information from the muscles is transmitted back to the brainstem, cerebellum, and cortex (not shown).

The primary outputs of the basal ganglia are to primary motor cortex and the ventromedial pathways.
The direct pathway between the basal ganglia and the motor cortex is excitatory for motor movement, whereas the overall effect of the indirect pathway through the internal globus pallidus (GPi) is inhibitory.

A motor unit consists of the extrafusal fibers innervated by a single alpha motor neuron.
A motor program is one in which a movement that, once triggered, continues automatically until its completion.

Alpha motor neurons cause the muscles to contact and lengthen. Gamma motor neurons innervate the muscles spindles in the belly of the muscle, maintaining firing of the alpha neurons in the presence of load and ensuring joint angles are constant under load.

Question 3

The Neuroanatomy of the Motor Systems

Answer 3

Pyramidal
Corticospinal (Cortex > spine one synapse)
Axons can exceed 1 meter
Origin layers IV, V primary motor cortex

Extrapyramidal
Origins: brain stem, basal ganglia, cerebellum
Terminate in spinal cord by function
Moderating influence by frontal Cortex

Question 4

pyramidal vs extrapyramidal

Answer 4

see slide 7 / 8 / 9

The brain innervates the spinal cord via the pyramidal and extrapyramidal tracts. The pyramidal (corticospinal) tract originates in the cortex, and almost all of the fibers cross over to the contralateral side at the pyramids. Tracts that do not travel through the medullary pyramids—the extrapyramidal tracts—originate in various subcortical nuclei and terminate in both contralateral and ipsilateral regions of the spinal cord. Termination is in the ventral horn of the spinal cords.

Question 5

The basal ganglia and the cerebellum are two prominent subcortical components of the motor pathways.

Answer 5

see slide 8
The basal ganglia proper include the caudate, putamen, and globus pallidus, three nuclei that surround the thalamus. Functionally, however, the subthalamic nuclei and substantia nigra also are considered part of the basal ganglia. The cerebellum sits below the posterior portion of the cerebral cortex. All cerebellar output originates in the deep cerebellar nuclei.

Even though the primary outputs of the basal ganglia are to primary motor cortex and the ventromedial pathways, the basal ganglia get input from all regions of the cortex.
As a person becomes proficient in a behavior, the control of the process is transferred to the basal ganglia.
Damage to the basal ganglia would be expected to produce difficulties in motor movements.
Damage to the caudate nucleus or putamen in rats would be expected to impair instrumental conditioning.

Cerebellum involves motor coordination, balance and eye movement calibration.

Question 6

Motor areas of the cerebral cortex.

Answer 6

Motor areas of the cerebral cortex. Area 4 is the primary motor cortex (M1). Brodmann area 6 encompasses the supplementary motor area (SMA) on the medial surface and premotor cortex (PMC) on the lateral surface. Area 8 includes the frontal eye fields. Inferior frontal regions (area 44) are involved in speech. Regions of parietal cortex associated with the planning and control of coordinated movement include S1, the primary somatosensory cortex, secondary somatosensory areas, and posterior and inferior parietal regions.

Question 7

Computational Issues in Motor Control

slide 11 example

Answer 7

Similarities in form
for different effector
systems illustrate
intermediate influence
on actions

Motor representations are not linked to particular effector systems. These five productions of the words cognitive neuroscience were produced by the same person moving a pen with the right hand (a), the right wrist (b), the left hand (c), the mouth (d), and the right foot (e). The productions show a degree of similarity, despite the vast differences in practice writing with these five body parts.

Question 8

Parameters involved in motor control

Answer 8

possible mental operations/computations:

1. seelection - eg match fingers to keys/notes
2. sequence > eg group notes into a phrase
3. Force > eg strike accented notes with greater force
4. timing > eg establish rhythm

Question 9

Goal Selection and Action Planning

Actions Goals and Movement Plans

Answer 9

The affordance competition hypothesis

Opportunities
Real-time
Evolved

Question 10

The affordance competition hypothesis

Answer 10

Cisek

Process of what to do (action selection) - competition part. This depends on internal drive states, longer-range goals, rewards and costs.

How to do it (specification) affordance component – we do what the environment allows us to do. We are always planning our next movement.

Question 11

affordance competition hypothesis sketch

slide 16

Answer 11

Schematic of the processes and pathways when choosing to reach for one object among a display of many objects. The multiple pathways from visual cortex across the dorsal stream correspond to action plans for reaching to the different objects. The thickness of the arrows and circles indicate the strength for each competing plan. Selection is influenced by many sources (red arrows). The movement (green arrow) results in visual feedback of the action and results in the competition starting anew, but now in a different context.

The motor cortex regions in the prefrontal lobes are important in the control and planning of complex motor sequences.
Lesions to the vestibulocerebellum lead to postural instability and difficulty in keeping one’s eyes fixed on a visual object despite head or body movements.

Question 12

The Brain–Machine Interface

Prosthetics

Answer 12

Motor neurons fire to code intended movements so …

Human machine interfaces are being built to give options for treating plegias and paralysis

Question 13

brain interfance steps

Answer 13

1.Record several
neurons in motor
cortex during lever-press
training

2. Connect neural interface
to robot arm. 
The population vector 
can be used to move the
arm

Question 14

brain training rats

Answer 14

Rats can be trained to use a lever to control a robot arm that delivers them drops of water. When several neurons in the primary motor cortex of the rat are recorded while the animal presses the lever, population vectors can be discerned that correlate with the actual movement. The experimenters then change the paradigm so that lever movement doesn’t control the robot arm, but rather the population vectors from the cells in the rat’s brain tell the robot arm where to move. Soon, all the rat has to do is think about moving the lever and the robot arm magically delivers water!

Question 15

brain machine interfaced example with MN

Answer 15

Brain–machine interface used by M.N. (a) The size of the implanted electrode device in relation to a U.S. penny. (b) A magnified image of the recording electrode array. (c) The location in the precentral gyrus where the electrode array was implanted. (d) The subject M.N. with the implanted device. He is controlling a cursor on the computer screen with his neural activity.

(e) The firing of one cell during four different conditions in which M.N. was cued to imagine moving his hand up, down, left, or right. The cell shown here fired best when M.N. imagined moving his hand to the right; other cells fired selectively when M.N. imagined moving his hand left, up, or down. When information from all of the cells recorded from the implanted electrode was combined, the desired direction of movement could be predicted. Once the BMI device learned how the pattern of M.N.’s activity correlated with the desire to move in these directions, M.N. could begin to use his intentions to move a cursor wherever he chose. Using this technology, M.N. was also able to open simulated e-mails, operate a television, open and close a prosthetic hand, and move a robotic arm. Such technology holds great promise for people like M.N., who cannot otherwise physically interact with their environment.

Question 16

Action Understanding and Mirror Neurons

Answer 16

mirror neurons

Neural structures activated by our own actions may be activated by observing the action performed by someone else.

This provides a basis for understanding the actions of others and observational learning.

Question 17

see slide 23 for example:
monkey do - 
monkey see and hear
see only
hear only

Answer 17

Responses of a single neuron in a monkey’s ventral premotor cortex during the performance or perception of different actions: (a) when the monkey itself breaks a peanut and views and hears the breaking of the peanut, (b) when the monkey watches someone else breaking a peanut and views and hears the breaking of the peanut, (c) when the monkey sees someone else breaking a peanut but cannot hear the peanut breaking, and (d) when the monkey hears but does not see someone else breaking a peanut. This neuron is considered a mirror neuron because it responds to actions that are undertaken by the monkey, as well as to actions that are viewed or heard by the monkey.

Distributed network of neural regions involved in action production and action comprehension (areas in premotor, parietal, and temporal lobes)
When we watch others, we understand what they are doing because our brain activates the neural structures that would be engaged if we were carrying out the action ourselves.
Single-cell recording studies have indicated that the supplementary motor area (SMC) may be especially important in the control of internally guided motor sequences, whereas the premotor cortex (PMC) may be especially important in the control of externally guided motor sequences.

Question 18

motor neurons in humans

Answer 18

Human action observation (dancing) areas are strongly involved
in performing the action itself. Shown here are brain activations in
experienced dancers who are watching someone else dance.

Figure 7.26 When skilled dancers observe a dance at which they are experts (versus a dance in which they have no expertise), they strongly activate premotor cortex (1, 2), intraparietal sulcus (3, 6), posterior superior temporal sulcus (4), and superior parietal lobe (5). These areas make up the neural network of action observation and include regions strongly involved in action itself, suggesting that these areas might represent the human mirror neuron system.

Question 19

Motor Disorders

Answer 19

Hemiplegia
Apraxia
Parkinson’s disease
Huntington’s disease

Question 20

hemiplegia

Answer 20

Loss of motor function on contralateral side
Common cause is haemorrhage in middle cerebral artery

Liepmann’s model of the neural regions associated with the production of skilled actions. The premotor areas of the contralateral hemisphere are essential for skilled movements of limbs. These areas receive input from the parietal lobe of the left hemisphere, an area assumed to store the representations of the actions. Thus, a lesion in the left posterior region will lead to apraxic movements with both contralesional and ipsilesional limbs.

Question 21

Apraxia

Answer 21

disorder of movement

1. Inability to link gestures into a 
coherent act (ideomotor)

2. Loss of ability to
   recognize the appropriate use of
   an object (ideational)

Question 22

apraxia motor test

Answer 22

Patients with apraxia may not be able to recognize skilled movements. (a) In the motor test, the patient is asked to pantomime a gesture such as using a key to open a door. (b) In the perception test, the patient views an actor pantomiming an action in three different ways, only one of which is appropriate. The patient must choose which action is correct. (c) Patients with either anterior or posterior lesions who produced apraxic gestures on the motor task were selected. Only the patients with posterior lesions showed impairment on the perception test. The apraxic patients with anterior lesions performed as well as nonapraxic, aphasic control subjects on the perception test.

Question 23

left parietal lobe

Answer 23

Left parietal lobe is key to
motor representation of an
Action

For example: it could represent
the position of ones body
and limbs relative to the position
of an object to pick up and the
changes needed to implement
the action

Question 24

The Basal Ganglia: Normal and Pathological

Answer 24

Differential neurochemical alterations in Huntington’s and Parkinson’s diseases. White links indicate excitatory projections, and black links indicate inhibitory projections. (a) In Huntington’s disease, the inhibitory projection along the indirect pathway from the striatum to the external segment of the globus pallidus (GPe) is reduced. The net consequence is reduced inhibitory output from the globus pallidus and thus an increase in cortical excitation and movement. (b) Parkinson’s disease primarily reduces the inhibitory activity along the direct pathway, resulting in increased inhibition from the globus pallidus to the thalamus and thus a reduction in cortical activity and movement.

Question 25

parkinsons

Answer 25

Radioactive tracers to label the distribution of specific neurotransmitters with PET.
New neuroimaging techniques are able to label the distribution of specific transmitter systems. This procedure provides an opportunity to visualize reduced dopaminergic activity in patients with Parkinson’s disease. Healthy subjects and Parkinson’s disease patients were injected with a radioactive tracer, fluorodopa. This agent is visible in the striatum, reflecting the dopaminergic projections to this structure from the substantia nigra. Compare the reduced uptake in the scan from a healthy subject (a) to the uptake in a patient’s scan (b).

Question 26

parkinsons DBS

Answer 26

Deep brain stimulation
Subthalamic nucleus
Globus pallidus

Periodic stimulation via
a pacemaker circuit

Deep-brain stimulation for Parkinson’s disease is achieved by the implantation of electrodes in the basal ganglia (most commonly in the subthalamic nuclei bilaterally, or the globus pallidus bilaterally). A pacemaker-like device is connected to the electrodes and implanted sub-cutaneously. The electrodes can then be stimulated by the pacemaker at regular intervals to relieve many of the symptoms of Parkinson’s disease.

Question 27

Huntington’s Disease

Answer 27

Characteristics
Age - 40s 50s
Irritable, absent minded, loss of motivation
Chorea – involuntary movements
Pathology
  Genetic -  Chrom.4 -> “huntingtin”
Stem cell treatment