Week 9: Cognitive Neuroscience Flashcards
Cognitive Neuroscience
Cognitive neuroscience: the study of the neurophysiological basis of cognition
Involves an understanding of the nervous system and of the individual units that comprise that system
Builds a bridge between neurophilopsgy/ biology of human brain which crosses to the human mind
Ancient Views of the Brain
Egypt (17th century BCE):
* Earliest known reference to the “brain”
Greece (~5th century BCE):
* Aristotle: heart is seat of the mind; the brain is
just a cooling center for the blood
* Hippocrates: “[People] ought to know that from the brain, and from the brain only, arise our pleasures, joys, laughter and jests, as well as our sorrows, pains, griefs and tears.”
But: “These things that we suffer all come from the brain, when it is not healthy, but becomes abnormally hot, cold, moist, or dry, or suffers any other unnatural affection to which it was not accustomed. Madness comes from its moistness.”
Not common knowledge that the brain is receipt of the mind
Brain appeared 8 times in ancient Egyptian writing
6/8 mentions come from this scroll
Air was vehicle of cognition
Aristotle thought it wasn’t lungs, it was the heart that was the seed of emotions
Brain was the cooling system for heart
Noticed that body temp on head is warm, so it cools off the blood
Not everyone agreed
Hippo: moisture part of brain is responsible for hallucinations
19th Century
Phrenology
Tab into the localization of function
Skull measurements and correlate them with personality traits
E.g., a bump on skull here explained
why brain area was bigger and responsible for advancement such as strong writing abilities.
They applied it to everyone even though only tested at one person
Racist and sexist policies
20th and 21st Century
Brain waves
Eeg caps
Technology that looks inside brain to check state of brain
Check neural activity
Fluctuations that occur that serve cognition
Levels of Analysis
Topics can be examined in multiple ways, from multiple different perspectives and angles (i.e., “viewpoints”).
Each “viewpoint” can add small amounts of information which, when considered together, leads to greater understanding
Computers - imagine birthday coming up and computer put you through life and everything so you want a new computer
High level analysis - does the computer have good battery, graphics etc
You could look at subcomponents
Go even deeper, look at structural components such as CPU and GPU
Even deeper, the type of GPU
This is a multi-level analysis
Building Blocks of Nervous System
Neurons:
cells specialized to create, receive, transform, and transmit information in the nervous system
Nerve Nets
1800s
Researchers didn’t have access to tools
Microscope would show a web type of image
Based on this, determined that neural tissue was comprised of nerve net
All of the connections were interconnected and signaling could go any way
Not much evidence that suggested contrary
INCORRECT
No Nerve Nets
Santiago Ramón y Cajal
Nobel Prize in 1906 With Camillo Golgi
Santiago alluciated community to neurons with the help of camillo
Golgi developed a new staining method
When apply stain to cell, only stained a fraction of cells in tissue
Stains them entirely
Cajal applied the stains to neural tissue and from newborn animals as they werent as dense
Cajal was also gifted artist and drew out the neurons that he saw
Still use them to this day
Neurons, not nerve nets
Neurons not all connected
Had sensible connections with eachother and created circuits
Staining allowed visualization of gap between neurons and synapse
Nerve Nets Cont.
Contradicted by the neuron doctrine:
Individual nerve cells transmit signals, and are not continuous with other cells
Neurons
They can look different from each other
All have dendrites - branch structures that stretch out from body
They pick up signals from other cells
Cell body - contains genetic material and other cells that transport and keep cell alive
Axon/nerve fiber - where info leaves cell body and sent to other neurons
Signals go down to axon terminal which another neuron will pick up signal
Synapse but dont touch with other neurons
Neuron before synapse - presnyaptic neuron
After synapse - postsynaptic neuron
Synaptic Transmission
- Post-synaptic potentials from dendrites and cell body summate at axon hillock. If threshold for an action potential (AP) is reached, an AP will fire down axon
- APs propagate down axon towards axon terminal
- Arrival of AP at axon terminal causes release of neurotransmitters, which diffuse across synapse & bind to receptors
- Causes electrochemical change in post- synaptic cell: post-synaptic potentials can be excitatory (EPSPs) or inhibitory (IPSPs)
Transmission
Neruon recieving info onto dendrite: causes change in voltage in neuron
Signals are called: postsnyaptic potentials: voltage difference where it changes across membrane
Charge changing onto one side of membrane to other
EPSP makes it more likely to fire (neuron), IPSP is less
How Neurons Communicate
Action potentials are signals fired down a neuron after it has received enough exiditory input
Pressure sensitive neuron - touched by something, fires depending on pressure of touch
Monitor shows action potential
Reference electrode - shows difference between inside and outside charge of cell
Go from -70 to +40 mv because of excitement
When it leaves, membrane voltage begins to drop and will eventually go back to resting when positive cells leave completely
Sometimes too many positive cells leave, so there is a refracter period which makes it not completely at rest
Last action potential lasts a millisecond
Either it happens or not
Coding for Stimulus Intensity
Light pressure: not firing too frequently
Medium: neuron starts firing more rapidly
Strong: starts very rapidly
Changing rate of what neuron fires can change way we experience different intensities of stimulations
Representation of the Brain
David Hubel and Torsten Wiesel: discovered feature detectors
Visual cortex has neurons that preferentially focus on different features of a stimulus
In cats
Electrodes into cats, recorded activity
Found that there were neurons that preferentially responded to bars of light at different orientations
In correct field for neuron, then it fired strongly
If not correctly, it was silent
Called these feature detectors
Researchers discovered this by accident as they shined black spots onto screen and black dot worked as it was slipping the peice of glass across the screen which gave a response
Visual Cortex Organization
Neurons in VC are organized in columns
All respond to same kind of stimulus (columns)
Depending on angle of bar light
ODC: left likes pink angle and white likes right
Critical Period for Visual Cortex Development
Much easier to learn language when infant
One eye covered, 3 weeks to 3 months of age, lose ability to digest info from the one eye
Can reverse this by covering the eye with both info
This can only occur from 3 week to 3 months in cat
Moving patterns can stimulate it
Failure of visual motor configuration
After couple of days, regains typical visual placing
Peak sensitivity : 28 days, one time exposure and prefer vertical edges
Hierarchical Processing
When we perceive different objects, we do in a specific order that moves from lower and higher parts of the brain
the ascension from lower to higher parts of the brain corresponds to perceiving object features that move from lower to higher levels of complexity
Perception focus
Receiving objects, brain does this in a way
Lower areas of cortex and as more aided competitions are required (e.g., water bottle from others), access higher/later of the brain to process this information
Combine edges and counters to form shapes
Higher processing: shapes get combined to form full objects
Re-enterant processing: go from simple to medium to complex features
Revisit areas to do so
Representation in the Brain
Group of neurons can differentially fire,
these patterns represent different kinds of neural representations
This can code for complex stimuli
3 types:
specificity
population
sparse
Specificity Coding
Representation of a specific stimulus by firing of specifically tuned neurones specialized just to respond to a specific stimulus
Within a set a neurons, one neuron is selective for stimulus and others are silent
Each face causes a different neuron to fire
Not enough resources to code for everything in world with just one neuron
Population Coding
representation of a particular object by the pattern of firing of a large number of neurons
Object such as face, represented by pattern of firing
Differential firing patterns within every population
Since you have different levels of firing, you actually now can code for wayyyyyy more stimuli
Sparse Coding
when a particular object is represented by a pattern of firing of only a small group of neurons, with the rest of the neurons remaining silent
Indicated by pattern of firing but smaller group of nuerons
Kind of a mix of both
Lobes of the Cerebral Cortex
Frontal cortex: front of head
Parietal: top
Occipital: back of head
Temporal: side of head
Insula: tucked in
Localization
Occipital lobe:
Vision
Parietal: primary receiving area for senses
Temporal: auditory, smell shared with frontal
Insula: taste, intrinsic sensations (disgust)
Frontal: coordination centre for all the senses, working memory, personality
Brain areas work together in complex tasks
Cerebral cortex: grey thin matter that covers brain, where axons are and send connections to other
Responsible for most of cognitive function and thinking
Brain damage: performed autopsy on brains and checked how damage impacted brain
Phineas Gage
Phineas Gage
Foreman, 1800s
1840s, blasting rock and one blast went of prematurely and metal rod went thru entire skull
Considered model employee, great guy before injury
Afterwards, personality completely changed
Become offensive, arrogant etc
Personality was biggest different to frontal cortex
Double Dissociation
When damage to one part of the brain causes function A to be absent while function B is present, and damage to another area causes function B to be absent while function A is present
Allows us to identify functions that are controlled by different parts of the brain
1 patient; 1 area of brain damage
To be sure that it was a specific area of brain responsible
To understand, another patient comes in to priortal cortex damage
If their social inhibition was intact and something else was different, this is double dissociation
Critical node in network, responsible for dissociation
Helps more confidence
Localization of Function: Language
Broca’s area: language production
Wernicke’s area: language comprehension
Broca: language production; apart of frontal cortex in motor adjacent area
Making movements with mouth etc
Brocas appashia: difficulty saying what they wanna say
Wernickes: temporal lobe; comprehension
Wernickes aphasia: could sound like english to a non-english speaker, essentially word salad
Also not able to understand what you are saying to them
Brain Imaging: MRI and fMRI
MRI: Magnetic Resonance Imaging
MRI: pictures of brain using very strong magnets
No radiation, xrays, they are high res pics using magnets
Can get 3D sense of what persons brain is like
fMRI: fMRI:
Functional Magnetic Resonance Imaging
2 different magnet fields, static
Measures changes in blood flow, where oxygenated blood is going
More blood pooling in regions that are more active
Using algorithm to detect oxygenated and deoxygented hemoglobin, scanner can pick up areas with increased blood flow -> brain activity
A bunch of protons in brain assolate at particular frequency, static field lines up protons from different tissues in particular and eventually protons relax
Since theres different desities, they rest at different rates, hence why there are darker areas in picture
Brain Imaging: PET
PET: Positron Emission Tomography
Image things such as glucose subtate, design ways to look at things that you are particularly interested in
First need to make radioactive tracer which houses unstable atoms
Put things in a big centrifuge, attack them with extra energy, protons, electrons which make unstable nucleotides
In blood, emit positrons, antimatter of election (positive), person sits inside pet scanner
Wait for postirons to be emitted
Positron will eventually collide with electron and annihalte together which produce 2 gamma rays that get shot at opposite sides of eachother at light speed
Pet scan picks these gamma rays up
Coincidence detectors: if they detect at same time, can say this part of brain was active
Everywhere where gamma rays cross at
180 degrees, shows on image
Not as good as fMRI, can be slower as well
Brain Imaging: EEG
EEG: ElectroEncaphaloGraphy:
* Records electrical activity on surface of the scalp
* Millisecond resolution
System where a bunch of electrodes are set on scalp of person and record fluctuations
Can also pick up muscle activations
Can be noisy from brain backround
Hairs etc ruin electrical signals
Brain Imaging: ERPs
ERP: Event-Related Potential
Average electrical activity at one site over many trials
Show participant same thing many time, and you get the average electrical activity
Temporal resoution
Brain Imaging: MEG
MEG: MagnetoEncephaloGraphy
SQUID:
Superconducting Quantum Interference Device
Measure magnetic fluctuations
Full of liquid helium which keeps sensors as cold as possible
Skulls, hair etc do not get smeared out
Do drop off but do not have any interference
Spatial resolution is pretty good, timing is good as eeg
Activation differences is best with fMRI
Combination, MEG is good
Brain Stimulation: TMS
TMS: Transcranial Magnetic Stimulation
Brain stimulation
Emit strong magnetic pulse above persons scalp
This pulse through unimpeded through skull until it meets some electrical tissue (neurons)
Can stimulate someones neuron without cutting head open
Temporal resolution is very good (millisecond level)
Spacial resolution (½ of square)
No need to wait for someone to get stroke
Can treat depression, migraines and tinitus and OCD
Apply multiple for treatment
6 months and do another round
Depression: not responding to treatment
Then you turn to TMS, the network is very active and networks have less energy
Target prefrontal cortex, anti-correlated to default network
Target default-node network and you are making an area that is connected but is not active
Brain Imaging: Evidence of Localization of Function
Fusiform face area (FFA)
* Inferior temporal lobe
* Responds specifically to faces?
* Damage to this area causes
prosopagnosia (inability to recognize faces)
FFA
Seems to really like faces
Fires when people see faces
If there is damage to this area, causes face blindness (doesnt mean you are blind from actual faces)
Wont be able to recognize face even if you know the person
Bird watchers, scanning them while watching different birds
You will see the same area light up
If you like cars, that area lights up
Parahippocampal place area (PPA)
Also inferior temporal lobe
Responds specifically to places
spatial layout; indoor/outdoor scenes
images of places
Extrastriate body area (EBA)
Responds specifically to pictures of bodies and parts of bodies
PPA and EBA respond to abstract concepts of “place” and “body”, respectively
Distributed Representation in the Brain
In addition to localization of function, specific functions are processed by many different areas of the brain
Many different areas may contribute to a function
May appear to contradict the notion of localization of function, but the two concepts are complementary
When you are actually behaving, parts of the brain are working together
Multi area coordination
Complementary to eachother
E.g., meeting friend in crowded cafe, recognize her and walk up to her (first face regonition lights up, or body recognition lights) and you say hello
Reading her facial reactions to yourself
How her emotional reactions are based on what she is saying
Many many brain areas functioning for this to work
E.g., ball (shape, colour, motion, depth, location)
All apart of network
Neural Networks
Groups of neurons or structures that are connected together
Can be examined using diffusion tensor imaging (DTI)
Mechanism for cognition must be dynamic & flexible
Areas that are commonly active (or inactive) at the same time are said to be functionally connected
Brain areas will (re-)configure into networks to subserve different functions or cognitive processes
Colours represent different directions that neurons are travelling
Also functional activity, brain activity are correlated in someway
2 brain areas are networked and connected if they are active and quiet at the same time
No need to be structurally connected to eachother
Although they are active at the same time since there is a third source connecting them
Certain areas are active during certain times
