Brain, Behavior, & Cognition- Exam 1

Invasive Measures

• Recording the electrical activity of neurons via microelectrodes implanted directly in the brain during brain surgery 

• Implanted microelectrodes and voltammetry probes detect electrical activity

• Microdialysis probes measure neurotransmitter concentrations

• Electroencephalography – recording electrical activity on the scalp

Noninvasive Measures

• Positron Emission Tomography (PET) – Radioactive tracer of metabolic activity (i.e. water, glucose)

• Functional MRI (fMRI) provides whole-brain maps of brain oxygenation

• Magnetic Resonance Imaging (MRI) – Similar to an X-ray image, but with a magnetic field/radio waves

what are the divisions of the Nervous System?

Central Nervous System

• brain

• spinal cord

Periphal Nervous System

• afferent

  • somatic

  • visceral

  • special

• efferent

  • somatic

  • autonomic

    • sympathtic

    • parasympathetic

    • enteric

Somatic 

• Relates the brain/body to the external world 

• Sensory and Motor inputs

• Voluntary and involuntary action

• What would be an afferent component of this system? How about an efferent component

Sympathetic Nervous System

• Fight, flight, freeze – arouses the body

• Reactions to threats and/or opportunities

• Think about physiological changes that occur during stress

Parasympathetic Nervous System

• “Rest and Regenerate”- returns the body to homeostasis

• Body wants to dispel tension – cannot remain “activated” all the time 

• Think about physiological changes that occur after a large meal

Enteric

• More neurons reside in the human gut than in the spinal cord (why?!)

• Innervation from Vagus nerve (Cranial Nerve X) but can operate even when it is severed

• Regulation of digestion, contraction of stomach muscles, secretion of enzymes

• Also has a curious connection to mood/emotion

Spinal Cord

• Structure which encases many nerves and coordinates the inputs and outputs of the peripheral nervous system

• The spine is segmented – each segment handles inputs to a specific region (dermatomes)

• Each segment contains a central canal surrounded by gray matter and white matter

• Gray matter – Neuronal cell bodies and localized connections

• White matter – Long-distance connections between neurons (we will learn why it is white when we discuss neuronal signaling) 

• Sensory input and motor output are separated: 

  • Sensory input enters via the dorsal nerve root

  • Motor output exits via the ventral nerve root

Central Nervous System (CNS) –

Brain & Spinal Cord

Peripheral Nervous System (PNS) –

Connects CNS to rest of the body (skin, muscles, internal organs)

Afferent pathways go from

the Peripheral Nervous System (PNS) to the Central Nervous System (CNS)

Efferent Pathways go from

the Central Nervous System (CNS) to the Peripheral Nervous System (PNS)

Enteric Nervous System

• More neurons reside in the human gut than in the spinal cord (why?!)

•  Innervation from Vagus nerve (Cranial Nerve X) but can operate even when it is severed

• Regulation of digestion, contraction of stomach muscles, secretion of enzymes

• Also has a curious connection to mood/emotion

Frontal Plane Image

Sagittal Plane Image

Horizontal Plane Image

Jerison’s Encephalization Quotient

• Ratio of actual brain volume compared to the expected brain size for a species of equivalent size

• Human EQ ~ 7.4-7.8 

• Crude measure of expected intelligence and complexity among animals

The developing brain has three distinct bulges which eventually develop into

forebrain, midbrain, and hindbrain

Forebrain later divides into

telencephalon and diencephalon

Hindbrain later divides into

metencephalon and myelencephalon

The midbrain is also called the

mesencephalon

Sonic Hedgehog pathway

• influential for cell differentiation 

• Primarily expressed in the prenatal human cortex 

Disruptions in the Sonic hedgehog  gene pathway can lead to

seizure disorders, language or cognitive impairment, down syndrome, hyperactivity, and/or schizophrenia

Three main structures to brainstem:

medulla, pons, midbrain

Medulla:

linked to breathing, heart rate, blood pressure; relays signals between cerebellum and cerebrum (cerebral cortex)

Pons:

linked to arousal, sleep, breathing, swallowing, bladder control, eye movement, facial expressions, hearing, equilibrium, and posture

Cranial Nerves

• in brainstem

• 10 of the 12 cranial nerves come from the brainstem (except for I and II which connect to the cerebrum)

• 2 sets of paired nerves which transmit sensory and motor information from CNS to PNS

• 6 of the 12 control the eye – why?

Facial nerve is also referred to as the

 intermediate nerve

The Midbrain coordinates

• survival and reproduction: 

  • Appetitive Behavior

  • Agonistic Behavior

  • Reproductive Behavior

In the midbrain, the Ventral Tegmental Area is the

Reward system and motivation (dopamine & substantia nigra)

In the midbrain, the Reticular Formation is the

Network of midbrain cells which regulate consciousness

 Cerebellum as “the little brain”

• Complex motor control center

  • Links memory & emotion

• Super densely packed tissue – surface area equal to ~80% of cortex surface area 

  • Many neurons packed densely into folds (lobules) 

• “Fractured” Somatotopy

• Much more advanced region than initially thought

• “Forward model” may also apply to social processing, not just movement

  • Intentional movement is predictive 

Hypothalamus:

• Homeostasis – Body’s tendency towards “set points” and equilibrium

• Controls the “basic drives” – hunger, thirst, sexual arousal, temperature regulation, sleep

The hypothalamus is the master control gland of the neuroendocrine axes via

signaling with the pituitary gland

 Thalamus:

Relay station of sensory data (EXCEPT smell)

• Relays sensory data to respective areas of the cerebral cortex

• Relays motor signals from cerebellum and basal ganglia (in the cortex)

• Also serves association areas in the cortex (integrative areas not solely dedicated to sensory or motor functions) – crucial role in motor planning

• Importance in integrated function

Frontal Lobe General Function

higher level cognitive functions (behavior& emotional regulation& planning)

Frontal Lobe Key Structures

• primary motor cortex

• prefontal cortex

• orbitofrontal cortex

• brocas area

Parietal Lobe General Function

primary sensory area; spatial awareness & perception

Parietal Lobe Key Structures

• primary somatosensory cortex

• precuneus

temporal lobe general functions

responses to the environment; communication/language'; memory access; emotions e

temporal lobe key structures

• limbic system

• wernicke’s area

• temporal gyri

• auditory cortex

occipital lobe general function

visual processing area; depth perception; color vision

occipital lobe key structures

visual cortexes

Four Lobes of the Cortex are

• frontal

• parietal

• temporal

• occipital

Corpus Callosum:

• The bridge between hemispheres

• plays a crucial role in interhemispheric communication, allowing information to travel between the left and right sides of the brain

Sasai et al. driving study – “functional split”

• Aimed to produce a “functional” rather than “anatomical” split within the brain

• Normal, healthy brains underwent driving simulation task(s):

  • Driving while listening to GPS directions

  • Driving while listening to radio broadcast 

• Identification of distinctive “driving network” and “listening network” in the split task condition

• Integration of networks was much higher in the GPS task

• Ability to switch between high and low integration networks corresponded to overall better driving performance

The limbic system

• Interconnected regions that integrates environmental stimuli (sensory input) with internal environment

• Key structures include hypothalamus, amygdala, hippocampus, some nuclei of brainstem and midbrain, certain circuits of the cortex (via basal ganglia)

The hippocampus acts as the

memory center of the brain (more on this in our memory lecture)

The amygdala triggers

emotional responses such as fear

The Neuron & its parts

• collect information (dendrites)

• integrate information (soma)

• conduct electrical signals (axon)

• transmit signals (axon terminals)

Hodgkin & Huxley: Squid Giant Axon & Voltage Clamp

• Attempted to measure viscosity of axoplasm with mercury

• Initial experiment was initially a failure – researchers pivoted focus

• Inserted fine capillary electrode to measure membrane potential – Led to first recording of intracellular action potential

• Discovery of voltage gated channels that controlled cell membrane potential

Voltage Clamp Method

• Allows researchers to keep membrane potential constant to measure activity of ion channels

• 0 mV is able to overcome threshold 

• Sodium is coming in, potassium is coming out

• When we isolate the channels the TTX blocks sodium 

• TEA blocks potassium so sodium channel works fine but there is no outward of K+

Membrane potentials

• Overall charge of the neuron is determined by differences in concentration between Na+ and K+ ions

• As resting state, this difference is about -70mv

• Sodium ions exist largely outside the cell at rest, while potassium is inside the cell

• These concentrations are maintained via the sodium potassium pump

• Cell as has a passive potassium leak channels selectively permeable to K+

Sodium Potassium Pump

• Binds 3 sodium ions and a molecule of ATP

• Splitting of ATP provides energy to change the shape of the channel. The sodium ions are driven through the channel

• The sodium ions are released to the outside of the membrane, and the new shape od the channel allows two potassium ions to bind

• Released of phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane

Events of Action Potential

• Upon sufficient stimulation voltage gated ion channels will open, causing sodium ions to leak into the cell

• The rush of positively charged ions causes the voltage to rise (become more positive) from -70mV

• Depolarization occurs as the cells charge gradually moves from -70 towards the positive values (up to about 40mv)

• As voltage becomes positive, potassium gated ion channels will open, causing potassium ions to leak out of the cell

• This causes the cells positive charge to decrease (become more negative)

• Repolarization occurs as the cells charge gradually moves from about +40 mv down to below- 70 mv. This overshoot is known as hyperpolarization

• A refractory period occurs due to hyperpolarization neurons require a short cooldown before firing another action potential

Depolarization occurs as

the cells charge gradually moves from -70 towards the positive values (up to about 40mv)

Repolarization occurs as

the cells charge gradually moves from about +40 mv down to below- 70 mv. This overshoot is known as hyperpolarization

A refractory period occurs due to hyperpolarization,

neurons require a short cooldown before firing another action potential

Graph of normal action potential

Influence of ESPS

Influence of IPSP

After an action potential occurs the electrical signal travels down the length of the

myelin sheath

• a lipid layer that acts like insulation of a wire

The mylein sheath contains gaps called

nodes of ranvier

• contain their own sodium & potassium channels

• To ensure the potential reaches the full length of the axons

  • the action potential resets at each node of ranvier- causing the signal to arrive to the axon hillock at full capacity 

• Mylenate only axons that need it- the ones that travel the farthest

Saltatory propagation

• In response to a signal the soma end of the axon becomes depolarized

• The depolarization spreads down the axon meanwhile the first part of the membrane repolarizes. Because Na+ channels are inactivated and additional K+ channels have opened, the membrane cannot depolarize again

• The action potential continues to travel down the axon 

 The Events at the synapse

• Upon reaching axon hillock- action potential stimulates voltage gated calcium channels

• Calcium ions cause vesicles with neurotransmitters to move towards the membrane and fuse with the membrane 

• The vesicle fuses with the membrane via SNARE proteins and neurotransmitters are released via exocytosis

• The cell sending signals is the presynaptic neuro

• The cell receiving signals is the postsynaptic neuron

The neurotransmitter Acetycoline (ACh) has the function of

Motor function (muscles); learning and memory

the neurotransmitter Dopamine has the function of

Reward system; movement regulation

the neurotransmitter endorphins has the function of

Pain relief; released during exercise; elevates mood

the neurotransmitter norepinephrine has the function of

Arousal; fight/fight response

the neurotransmitter serotonin has the function of

Natural mood booster, sleep/wake cycles; lower serotonin levels linked to depression

the neurotransmitter GABA (gamma aminobutyric acid) has the function of

Lowers arousal and reduces anxiety; primary inhibitory neurotransmitter

the neurotransmitter Glucamate has the function of

Primary excitatory neurotransmitter of the Central Nervous System (CNS)

What would happen if the nervous system poison Tetrodotoxin (TTX) was present

______ is a neurotoxin that selectively blocks voltage-gated Na+ (sodium) channels… so…

• Sodium is what makes it go up (depolarization) 

• Since action potential is contingent on sodium

• the action potential doesn't really happen

• falls flat

What would the graph look like if the nervous system poison Tetrodoxin (TTX) is present

What would happen if the nervous system poison Tetraethylammonium (TEA) was present

Able to depolarize but since only the K+ (potassium) channels are blocked the repolarization process is delayed 

1. Slowly starts to level out

2. Not a dramatic level of spiking down

3. Takes a lot longer for repolarization to occur

What would the graph look like if the nervous system poison Tetraethylammonium (TEA) is present

Archetypes of neural networks

1. Feedforward excitation

2. Feedforward inhibition

3. Convergence

4. Divergence

5. Lateral inhibition

6. Feedback excitation

7. Feedback inhibition

Feedforward excitation

Neuron relays information to its neighbor

Feedforward inhibition

A presynaptic cell excites an inhibitory interneuron which then inhibits the next cell

Lateral inhibition

•  A presynaptic cell excites inhibitory interneurons, inhibiting neighboring cells in the network

  • important for vision

Feedback excitation is involved

in learning/memory

Feedback inhibition is important

for circadian rhythm

Convergence

One postsynaptic cell receives convergent input from many presynaptic cells

Divergence

any individual neuron can make divergent connections to many different postsynaptic cells; crucial for stretch reflex

Structural neuroplasticity

the brain changes as a result of learning/experience

Functional neuroplasticity

neuronal remodeling following dysfunction/injury

Homouncolous Model

• Way of visually representing how visual and sensory cortex map out on body

• Body plan changes are reflected in the brain

• This includes both somatosensory and motor cortex

• Not a part of the brain, but a way of representing cortex’s

Phantom sensation

the phenomenon where amputees report sensations in their missing limbs

Phantom limb pain

magnitude of pain correlates with extent of remodeling in the cortex

• treatment- mirror

D.M Case Study

• Right arm amputee (above elbow)

• Reported to be able to feel and move her right forearm, hands, and fingers

• Touch on the right side of face was also felt in missing limb

• Chin and jawline are next to hand in the homunculus

Somatosensory Cortex rewiring

Making use of available tissue in brain

Plasticity during youth vs. adulthood

• Brains are most “plastic” during youth 

• Our brain is like a sponge- we don't have any innate functions

• we have to be primed to learn more

  • more than other animals

  • not born with innate wiring

• Adults are pushed to focus and hone skill

  • cholinergic neurons provide focus and inhibit unwanted plasticity

Critical/Sensitive Periods

• babied/children need to learn- cholinergic neurons are more primed for activation

• Adults are pushed to focus and hone skill- cholinergic neurons provide focus and inhibit unwanted plasticity

• “Flexibility vs skill” tradeoff

Experience expectant neuroplasticity

the brain contains wiring predisposed for “expected” experiences

Experience dependant neuroplasticity

additional growth that varies greatly within individual experiences

Sperry’s Frogs (Chemoaffinity Hypothesis)

• Brains innate wiring is due to predefined chemical signaling

• Experience independent hypothesis- this mechanism is not influenced by an animal's experience of the world

Held & Hein’s Kitten Study – Procedure and Takeaway

• One of the cats was guiding and could walk around while the other could not walk; only see where it was being pulled bc of the first cat 

• vision develops in response to understanding of causal relationship between motor actions and visual field

• The way you interact with the world changes how your vision develops

• Vision tested in response to 

  • Visually guided paw placement

  • Depth perception (visual cliff)

  • Blink (“flinch”)  in response to approaching object 

• The way you engage in the world leads to development of normal vision