The Acting Brain (midterm 5)

Question 1

•Utilization:

Answer 1

compulsively use objects in view (if they see a broom, they’ll start sweeping; there’s no awareness).

Question 2

•Perseveration:

Answer 2

keep repeating actions that are no longer useful

Question 3

Disorders of cerebellum and
basal ganglia result in

Answer 3

strategy without tactics

Question 4

Summary: Execution

Answer 4

• Skeletal muscle consists of muscle fibers or myocytes
• Muscle fibers innervated by axons of lower motor
neurons
• Lower motor neurons have their cell bodies in spinal
cord (ventral horn)
• Upper motor neurons in primary motor cortex project
downwards via multiple pathways
▫ Main one is corticospinal tract

Question 5

Cerebellum

Answer 5

Cerebellum
• Coordination of movement, especially multi joint, i.e.
the movement that you want to make happens at the
right time and occurs accurately (e.g. correct distance
and strength)

Many movements are “multi-joint” eg reaching to pick something up requires precise timing of individual movements and joints

Question 6

Innervation of skeletal muscle

Answer 6

• Muscle contraction is directly controlled by lower motor neurons • Each myocyte gets innervation from only one lower motor neuron • But a single lower motor neuron innervates many myocytes

** point where lower motor neurons contact muscle cells is the neuralmuscular junction

Question 7

TACTICTS

level & structures

Answer 7

MIDDLE : Specific actions needed to perform goal

Primary motor cortex

Premotor cortex

Basal ganglia

Cerebellum

Question 8

Basal ganglia loops

Answer 8

• Direct pathway:
accelerator
(promotes
movements)

• Indirect pathway:
brakes (decreases
movements)

* two pathways back from the BG to the motor cortex.

ACCELERATOR - increase movements

BRAKES - decrease movements

Question 9

Huntington’s disease

Answer 9

• Reduced output of
indirect pathway
(“brakes”) but normal
output on direct pathway
(“accelerator”)

• The shift in balance
promotes movement in
general

-Arises in middle age (~40s)
• Symptoms: Excessive movement, dance-like flailing
limbs (chorea) and contorted postures
▫ https://www.youtube.com/watch?v=OveGZdZ_sVs

Question 10

Premotor cortex and Supplementary
motor area (SMA)

Answer 10

Premotor cortex and Supplementary
motor area (SMA)
• Modulate activity of M1

• Stimulation does not
result in movement

• Involved in motor
planning

• NOTE: In textbook, premotor
cortex = lateral premotor cortex
and supplementary motor area =
medial premotor area

Question 11

Supplementary motor area (SMA):​

Answer 11

organizing internally generated actions
• SMA
▫ Receives input from brain areas that represent the
position of the limbs
▫ Learned (internally generated) action patterns that do
not require feedback from the environment, but simply
from the position of the limbs (e.g. playing a familiar
song on the piano)

Question 12

Parkinson’s disease

Answer 12

• Degeneration of
substantia nigra
• Increase output of
indirect pathway
(“brakes”) and
decrease output on the
direct pathway
(“accelerator”)
• Results in difficulty
with self-initiated
movement

-Parkinson’s Disease
• Affects 0.15% of the population; Onset ~60 years
• Impaired:
▫ Self-initiated movements
• Symptoms
▫ Resting tremor
▫ Slow movements
▫ Difficulty initiating movements

Question 13

Mirror neurons : premotor cortex

respond when?

Answer 13

Mirror neurons:
Premotor cortex
• Respond when:
▫ Monkey performs action
• Specific to particular actions
• Also respond when monkey
observes experimenter
performing action
• Do NOT respond when object
moves on its own
▫ Purposeful action is critical

Question 14

Hierarchical organization of action

Answer 14

• Strategy: high-level goals and plans ( make coffee)

• Tactics: specific actions needed to achieve goals (▫“Add water to coffee pot, measure coffee, add coffee…”)
• Execution: neural signals and muscle movements needed to carry out tactics (▫E.g. muscle movements needed to grasp coffee pot)

Useful distinction: strategy vs. tactics vs. execution

Old distinction from military: described by General Sun Tzu

Strategy: big picture, aim is to win the war. Would be good to have a trench in a certain place.

Tactics: actions needed to make the trench happen. Certain number of soldiers, have to do certain things in certain order.

Execution: actually digging the trench, holding the shovel etc.

Question 15

Hemiplegia

Answer 15

Damage to one side of the primary motor cortex results in a failure to voluntarily move the other side of the body.

Question 16

Basal ganglia (vs. cerebellum: important in coordination of movements)

Answer 16

• Caudate, putamen, globus pallidus, substantia nigra
• Modifies activity in frontal motor structures
• Important in initiation and execution of movements
• Damage leads to excess movement or insufficient movement

▫Parkinson’s, Huntington’s

Question 17

Motor loops: Cerebellum and basal
ganglia

Answer 17

Motor loops: Cerebellum and basal
ganglia

• Not involved in choosing what movements to make
• Set particular movement parameters (e.g. force, duration of
movement)
• Control/modulation movements in progress
How motor loops
work:
get information from
the motor cortex, do
some processing,
send information
back.

Question 18

Executing Action: Primary Motor Cortex (M1)

Answer 18

• Located in precentral gyrus of frontal lobe
• Somatotopically organized and crossed (left hemisphere = right side of body)
• Stimulation results in movement and lesion results in paralysis (e.g. hemiplegia)

Somatotopically organized: neurons for controlling movement in adjacent parts of the body are located in adjacent areas on precentral gyrus

Some parts of the body have more area in M1 devoted to controlling them – why?

Question 19

Organizing principles Hierarchical organization of action

Answer 19

Execution: Muscle cells, lower motor neurons, the spinal cord

Strategy vs. tactics: The brain Understanding the actions of others

Question 20

Amyotrophic lateral sclerosis (ALS)

Answer 20

• Symptoms:
▫ Early: Muscle weakness and atrophy
▫ Late: Loss of all voluntary movement, ability to speak,
breathe, swallow
• Death of upper and lower motor neurons
Doesn’t affect intellect
Cause not well understood

Question 21

MOTOR SYSTEM AND UNDERSTANDING THE ACTIONS OF OTHERS

Answer 21

* A DETOUR INTO SOCIAL NEUROSCIENCE

Why talk about understanding the actions of others in a class on the motor system?

Turns out that we use our own motor system to understand other peoples’ actions.

Question 22

So we’ve got these lower motor neurons that directly control the muscle cells.

They have their cell bodies in the spinal cord and they send their axons out through the spinal nerves to contact the muscle cells.Where are they getting information from?

Answer 22

From the brain!

What do we call information leaving the brain?

Efferent

So there must be neurons in the brain that send their axons out down the spinal cord.

•Lower motor neurons receive innervation from upper motor neurons

▫Upper motor neurons have their cell bodies in the brain (primary motor cortex, M1)

▫Axons run downward through different spinal pathways that control different muscle groups

▫Most important is the corticospinal tract

Question 23

Neural substrates of action :

Level || Function || Structures

Answer 23

High || Strategy || Prefrontal cortex

Middle || Tactics || Primary motor cortex, Premotor cortex, Basal ganglia, Cerebellum

Low || Execution || Spinal cord, Motor neurons, Muscle cells

Question 24

Mycoytes and their innervation

Answer 24

▫AKA muscle cells or muscle fibers

• Muscle contraction is directly controlled by lower motor neurons
• Each myocyte gets innervation from only one lower motor neuron
• But a single lower motor neuron innervates many myocytes

Question 25

OVERVIEW •Motor system is hierarchically organized ▫Execution: ▫Tactics: ▫Strategy: •We may understand the actions of others by...

Answer 25

▫Execution: muscle cells, lower motor neurons, corticospinal tract ▫Tactics: M1, SMA, PMC –Cerebellar and basal ganglia loops are involved in fine-tuning and coordinating actions ▫Strategy: prefrontal cortex •We may understand the actions of others by representing/simulating the motor actions it would take to perform their behavior

Question 26

• Axons run out to muscles via spinal nerves

Answer 26

Axons don’t leave the spinal cord at random

Question 27

Effects of trans Randal stimulation over SMA

Answer 27

Question 28

Implications of mirror neurons

Answer 28

•We may understand the actions of others by simulating the motor programs it would take to perform the same behavioR ## Footnote * People with autism have trouble understanding others’ goals and may have impaired mirror neurons * Embodied cognition: complex cognitive processes stem from our body’s interaction with the environment. *If I see you do something, my brain actually computes what motor commands would be needed for me to perform the same action.* *My goals in performing that action are associated with the movements needed to perform that action.* *When I was performing this action, what was my goal? Can use this to figure out someone else’s goal.* ***You can figure out the other person’s goals based on the movements they’re making*** ***Embodied cognition: the mind depends on the body*** ***Mirror neurons are about representing what you do with your body: premotor cortex*** ***We can’t understand other people without using representations of the body.***

Question 29

Primary motor cortex

Answer 29

Responsible for execution of voluntary movements of the body.

Question 30

EMBODIED COGNITION

Answer 30

Embodied cognition: the mind depends on the body Mirror neurons are about representing what you do with your body: premotor cortex We can’t understand other people without using representations of the body.

Question 31

Cerebellum loops & ataxia

Answer 31

Touch nose with finger Think about what’s involved: move shoulder, elbow, wrist simultaneously Cerebellar patients can’t do this: might do the movements sequentially, or might overshoot or come up short Clumsiness due to alcohol: depression of cerebellar circuits

Question 32

Skeletal muscle

Answer 32

• Muscles are attached to the skeleton by tendons • Cause movement by contracting ▫ Muscles can only pull; cannot push ▫ Often organized into antagonistic pairs so joints can be moved in different directions • Made up of many myocytes ▫ AKA muscle cells or muscle fibers

Question 33

Types of muscle

Answer 33

• Smooth muscle ▫ Lines digestive tract, arteries ▫ Controlled by autonomic nervous system • Striated muscle ▫ Cardiac Heart muscle ▫ Skeletal Voluntary movement Muscle around joints, eyes, respiration, facial expression, speech

Question 34

How do neurons in primary motor cortex code for movement?

Answer 34

If there are many neurons with many preferred directions, how is a single movement executed? Does one neuron decide? Cannot be: preferred directions of each neuron are much broader than precise movements) Does a population of neurons decide?

Question 35

antagonistic pairs

Answer 35

Define Add slide

Question 36

REPRODUCING ACTION

Answer 36

* Mimicry: Watch what they do, make the same movements * Imitation: Watch what they do, figure out their goals, reproduce actions based on goals * Can one person be imitating another if they don’t perform exactly the same actions?

Question 37

Premotor cortex: acting with objects in the environment

Answer 37

* Receives input from dorsal visual stream * Actions triggered by the environment ▫E.g. “pull handle when light is blue, rotate handle when light is red” ▫Lesions prevent these associations from being formed •Single-cell recordings: Premotor cortex responds when an external cue requires movement, but not when monkey moves spontaneously \*\*\*\* Whereas SMA is involved in organizing internally generated actions, premotor cortex organizes acting with objects in the environment Acting with objects in the environment (e.g. reaching for a coffee cup ---- Dorsal visual stream: location of objects in the environment

Question 38

STRATEGY (FUNCTION AND STRUCTURE)

Answer 38

THE PRREFRONTAL CORTEX ## Footnote •Prefrontal cortex: everything anterior to SMA and premotor cortex high-level goals and plans •Prefrontal damage results in tactics without strategy (no problem executing actions, but have a problem with the goals)

Question 39

PREFRONTAL CORTEX

Answer 39

* Not directly involved in programming actions * Instead, involved in selection of goals and corresponding actions * Lesions can result in disorganized actions that don’t fit goals (but actions themselves are normal) * Perseveration: keep repeating actions that are no longer useful * Utilization: compulsively use objects in view (if they see a broom, they’ll start sweeping; there’s no awareness). E.g. trouble making coffee: have to set up and maintain a series of subgoals to achieve your main goal ---- \*But no problems with the actions themselves Perseveration: deck of cards, sort by suit, then instructed to sort by color; keep sorting by suit Utilization: people believe they are acting normally

Question 40

• Lower motor neurons have their cell bodies in the spinal cord ▫ Ventral horn: motor ▫ Dorsal horn: sensory

Answer 40

\*\*\*\* SPINAL CORD - ADD IMAGE {important)

Question 41

Structure of a skeletal muscle

Answer 41

ADD SLIDE

Question 42

Spinal Cord - Ventral and Dorsal Horns

Answer 42

Spinal cord consists of grey matter and white matter So are the cell bodies are in the in the grey matter part Horizontal cross section of spinal cord Central core of grey matter (H shape) Projections are called horns Ventral horns: motor Remember this because you usually move forward and ventral is towards your stomach Dorsal horns: sensory If the cell bodies are in the spinal cord and the axon terminals are on the distant muscles, what route do the axons follow?

Question 43

The neuromuscular junction

Answer 43

• Specialized synapse that connects lower motor neurons and skeletal muscle • Lower motor neurons send action potentials along their axons • Releases the neurotransmitter acetylcholine onto muscle fibers, resulting in contraction • Some arrow poisons block acetylcholine ▫ How does this kill?

Question 44

Population vector

Answer 44

The sum of the preferred tunings of neurons multiplied by their firing rates.

Question 45

Population coding in M1

Answer 45

Different cells have different tuning curves Movement direction can be coded by the summed activity of multiple motor cortex neurons (i.e. the population vector), each contributing their own vote. Here, 241 cells from motor cortex each contribute a vote. \*Predictive power of population coding is beginning to be harnessed in use of prosthetics.