Reg. of Motor Control and the Limbic System (Week 2, Mod 8)

What are the 3 major components of the Telencephalon?

1) Cerebral cortex

2) Limbic system

3) Basal ganglia

What are the 4 major components of the Diencephalon?

1) Thalamus

2) Hypothalamus

3) Pituitary gland

4) Mammillary bodies 

What is the Rhinencephalon of the brain?

The area of OLFACTORY processing in the brain

• Different sizes through species; humans is small, while dog is large

What is the general function of the limbic system?

Is primarily involved in the control of EMOTION, learning, and memory 

What are the 6 major divisions of the limbic system?

1) Hippocampus

2) Amygdala

3) Mammillary body 

4) Fornix

5) Septum 

6) Cingulate cortexes (L and R)

Structures are arranged differently according to species… specific to us as individuals 

What is the function of the hippocampus?

Is great for spacial orientation, and memory for an individual’s location within a space

• Is also good for LONG TERM MEMORY

• Basically spacial awareness, spacial navigation, and memory of being in a place

What are the 3 major structures of the hippocampus? What are the 2 different kinds of hippocampal cells, and what are their functions?

Has two layers:

• CA1

• CA3

• Dentate gyrus fills the space between the two layers

Made of 2 types of cells, each has its own function:

• ‘Grid’ cells - provide a universal neuronal coordinate system for spatial navigation 

• ‘Place’ cells - activated ONLY when the animal is in a specific place

What are 2 examples of explicit memories? What structure in the brain is responsible for them?

1) Facts

2) Events 

• The HIPPOCAMPUS is responsible for maintaining these memories

  • Remember, good for LONG TERM memory 

What are 4 examples of implicit memories, and what structures in the brain are responsible for each?

1) Priming - memory due to repetition; i.e. when you repeat a number over and over to memorize it

• Neocortex is responsible for this

2) Skill / habits

• Facilitated by striatum

3) Conditioning - TWO TYPES

• Emotional response - facilitated by AMYGDALA

• Skeletal muscle response - facilitated by cerebellum

4) Habituation / sensitization - is a REFLEX, but can be unlearned

• Facilitated by SPINAL CORD

What would happen if the hippocampus were to be removed from the brain? Think of what is effected, and what WOULDN’T be affected.

Though the hippocampus is central to long term memory and spacial awareness, it is not responsible for ALL kinds of memory / spacial ability

• Without hippocampus, an individual would lose EXPLICIT memory

  • Facts, events

• But IMPLICIT memory would remain intact

Motor memory also remains intact

What is the function of the amygdala?

Is crucial for SENSORY and EMOTIONAL MEMORIES 

• Often is responsible for the BEHAVIOR of the animal, both innate and learned behavior, based on the animal’s sensory and emotional memories to certain incidents 

• Forms sensory cues: olfactory, visual, auditorial, pain; ASSOCIATIONS of an animals environment with these senses are formed here 

Think A = ASSOCIATION = AMYGDALA 

What are the two different brain nuclei in the amygdala?

Basolateral nuclei

Central nucleus 

• Have slightly different functions depending on species 

Describe the species variation of the amygdala… in what ways is it different? In what ways is it the same?

There is HIGH species specific variation when it comes to representation of the environment 

• You are going to perceive your environment and form different associations with it from Ike

  • Cues going into our amygdalas will be different

• BUT THE LEARNING OF THESE CUES IS THE EXACT SAME ACROSS SPECIES 

  • This is why we can use rats to study human behavior 

What is the paraventricular nucleus within the central nucleus of the amygdala?

Is the part of the amygdala that is responsible for STRESS

• Associates stress with other senses (i.e. pain → smell, sound, or visual cue)

• Is essentially the fight or flight response of our brains

• Is the EXACT SAME PATHWAY ACROSS ALL SPECIES

What would happen if there was damage to the amygdala?

Animal (for this example, lets say cat) will try to mate with ANY ANIMAL

• Male cat will try to mate with other males, dogs, beavers, etc.

Will also show a LOSS in the FEAR response; will not perceive obvious threats and will wander about without caution 

This all essentially shows that the amygdala is CENTRAL in fostering species-specific behaviors (i.e. a cat knowing its not advantageous to try and mate with a dog) and perceiving possible threats 

What is a classic example of the amygdala forming a LEARNED association?

Pavlovian response: Rat being shocked when a certain sound is played → eventually learns to fear that sound even if they don’t get shocked later on

What EXACTLY is the fornix, and what is its function?

Is a bundle of nerve fibers along the medial aspects of the two cerebral hemispheres

• Has inter-connections with the hippocampi on both sides of the cerebral hemispheres

Is essentially what connects the hippocampus to the MAMMILLARY BODY, relaying info FROM the hippocampus directly to the mammillary body 

What would happen if there was damage to the fornix?

Memory impairments / diseases, such as:

• Dementia 

  • Caused by demyelination of the nerve fibers in the fornix; results in cognitive dysfunction, short term memory impairments, and long-term memory impairments

• Alzheimer’s 

• Schizophrenia 

What is the mammillary body, and what is its function?

The mammillary body is intricately connected with the hippocampus, fornix, amygdala, and midbrain

Primary function: Associated with RECOLLECTIVE memory (LEARNING), but also is involved in emotion and goal-directed behaviors

- Also involved in the formation of NEW memories (anterograde memory)

What would happen in the brain if the mammillary body were damaged?  What are some ways it can become damaged?

Trauma, stroke, tumors, and alcoholism cause significant damage to mammillary bodies.  The result is anterograde amnesia and reduced motivation

- You know when you black out drunk and can’t remember certain things happening?  Yeah, thats cause this guy is gettin damaged 

What is the septum, and what is it involved in?

Septum = RAGE

• Involved in emotional behaviors, sexual behavior, and aggressive behavior

• Also has attention and memory functions

Is simply a MODULATOR of these behaviors, but is not the main driver

• Modulates the INTENSITY and PROBABILITY of these behaviors occurring

• Receives input from the hippocampus, amygdala, hypothalamus, and midbrain

What would happen if there was damage to the septum?

Lesions to the septum INDUCE RAGE

• Individual can no longer gauge / check their own behavior

  • Exaggerated reactivity to both appropriate AND innocuous stimuli

What is the cingulate cortex, and what is its function?

Is a neural interface between emotion, sensation, and action

• Takes our emotional state and turns it into a planned motor response / behavior

  • Associated with PLANNED behaviors

Is essentially the connection between our LIMBIC and MOTOR systems

What would happen if there was damage to the cingulate cortex?

INDIFFERENCE TO PAIN, and other sensations that have strong emotional connotations

• Social indifferences and apathy, eliminates emotional intonation in speech, adn causes personality changes 

What exactly is the basal ganglia?  What is its function?

The basal ganglia is a set of FOUR NUCLEI that are involved in the control of VOLUNTARY movement.  These nuclei are the:

1) Caudate nucleus

2) Putamen 

3) Globus pallidus 

4) Substantia nigra 

Describe the way the basal ganglia communicates with the rest of the brain…

DOES NOT have direct input or output with the spinal cord

• Instead, gets input from the CORTEX, and directs output to the MIDBRAIN 

• Another output pathway happens via the thalamus, which projects to the frontal, premotor, and motor cortices 

Has both EXCITATORY and INHIBITORY pathways 

What is the main neurotransmitter that drives the function of the basal ganglia? What effect can it have on the basal ganglia depending on the receptor it binds to?

The main neurotransmitter that drives the basal ganglia is DOPAMINE

• Acts specifically in the PUTAMEN to drive a direct motor program that facilitates movement 

• At the same time, INHIBITS the probability of a voluntary behavior 

  • Has opposing effects based on the receptor it binds to (D1 = excitatory, D2 = inhibitory)

What is the direct cause of Parkinson’s disease?

LOSS OF DOPAMINE → results in an INCREASED INHIBITORY OUTPUT of the basal ganglia

• The overactivity of this indirect pathway results in hypokinetic disorders (i.e. impaired initiation of movement and REDUCED voluntary movement)

  • This is why we have the uncontrollable shakiness we see in people with Parkinson’s 

  • The nucleus directly responsible for this increased inhibitory output is the Globus pallidus

Describe the hierarchy of motor control… describe the pathway starting from initial sensory input

Sensory input → limbic system → drives motivation for movement 

limbic system → basal ganglia → initiates the movement 

basal ganglia → cerebellum → coordinates movement 

cerebellum → motor cortex → refines the movement 

motor cortex → spinal cord → movement made 

What are “pyramidal tracts” in the brain, and what is there function?  What, then, are extrapyramidal tracts?

Pyramidal tracts are MOTOR NEURONS that originate in the frontal cortex and terminate in the spinal cord or brainstem 

• Are essentially DESCENDING pathways that control motor responses 

EXTRApyramidal tracts instead originate in the pons and medulla of the midbrain; involved in INVOLUNTARY movement 

What is the name of the pyramidal tract that runs down the spine of all animals? What is its function, and how does it vary between species?

Corticospinal tract

• Is required for FINE MOVEMENT (recently evolved, new)

• Is different across species depending on how much they would need fine movement (ex: a dog will have more dependence on the corticospinal tract than an ungulate)

What are the names of the 4 extra-pyramidal tracts, and what are their functions?

1) Reticulospinal tract -

• OLD tract, is responsible for basic instincts (startle reaction), postural, and initiates locomotion 

2) Vestibulospinal tract - 

• Input from vestibular apparatus and cerebellum; acts on extensor muscles 

  • Maintains posture 

3) Rubrospinal tract - 

• Acts mainly on flexors, postural in function 

4) Tectospinal tract - 

• Input from vision and hearing, acts on cervical vertebrae, and orientates head

What would you see in a patient that has damage to the pyramidal tract?

Spasticity and paralysis

What would you see in a patient that has damage to a extra-pyramidal tract?

INVOLUNTARY movements, muscle rigidity, and immobility WITHOUT paralysis